View source for Fusion power

{{Short description|Electricity generation through nuclear fusion}}
{{Distinguish|Fusion of powers}}
{{Use mdy dates|cs1-dates=ly|date=June 2020}}

{{multiple image
| perrow            = 2/2/2/1
| total_width       = 410
| image1            = Scylla I in 1958.jpg
| image2            = Tokamak T-1.jpg
| image3            = 
| image4            = JET cutaway drawing 1980.jpg
| image5            = PFRC 2 pulse.jpg
| image8            = EAST Tokamak plasma image3.jpg
| image9            = Preamplifier at the National Ignition Facility.jpg
| footer            = From top, left to right
# [[Scylla I]], the first device to achieve laboratory thermonuclear fusion
# [[T-1 (tokamak)|T-1]], the first [[tokamak]] device
# [[Joint European Torus]], the first device to fuse [[deuterium-tritium]] plasma
# [[Princeton field-reversed configuration|Princeton FRC]], a modern [[field-reversed configuration]] experiment
# Fusion plasma in China's [[Experimental Advanced Superconducting Tokamak]]
# The [[National Ignition Facility]], the largest [[inertial confinement fusion]] experiment and first to achieve [[fusion ignition]] and [[scientific breakeven]]
# [[ITER]], the largest [[magnetic confinement fusion]] experiment, scheduled to operate from 2034
| image10           = ITER Tokamak and Plant Systems (2016) (41783636452).jpg
}}
'''Fusion power''' is a proposed form of [[power generation]] that would generate [[electricity]] by using heat from [[nuclear fusion]] reactions. In a fusion process, two lighter [[atomic nuclei]] combine to form a heavier nucleus, while releasing energy. Devices designed to harness this energy are known as fusion reactors. Research into fusion reactors began in the 1940s, but as of 2024, no device has reached net power, although net positive reactions have been achieved.<ref name="NYT-209221213">{{cite news |last=Chang |first=Kenneth |title=Scientists Achieve Nuclear Fusion Breakthrough With Blast of 192 Lasers – The advancement by Lawrence Livermore National Laboratory researchers will be built on to further develop fusion energy research. |url=https://www.nytimes.com/2022/12/13/science/nuclear-fusion-energy-breakthrough.html |date=13 December 2022 |work=[[The New York Times]] |access-date=13 December 2022}}</ref><ref name="Ignition">{{Cite news |date=2022-12-13|title=DOE National Laboratory Makes History by Achieving Fusion Ignition|work=US Department of Energy|url=https://www.energy.gov/articles/doe-national-laboratory-makes-history-achieving-fusion-ignition|access-date=2022-12-13}}</ref><ref>{{Cite web |author=Vogt |first1=Adrienne |last2=Hayes |first2=Mike |last3=Nilsen |first3=Ella |last4=Hammond |first4=Elise |date=2022-12-13 |title=December 13, 2022 US officials announce nuclear fusion breakthrough |url=https://www.cnn.com/us/live-news/nuclear-fusion-reaction-us-announcement-12-13-22/index.html |access-date=2022-12-14 |website=CNN |language=en-us}}</ref><ref>{{cite news |last1=Gardner |first1=Timothy |title=US scientists repeat fusion ignition breakthrough for 2nd time |url=https://www.reuters.com/business/energy/us-scientists-repeat-fusion-power-breakthrough-ft-2023-08-06/ |access-date=13 February 2024 |work=Reuters |issue=Dec 13, 2022}}</ref>

Fusion processes require fuel, in a state of plasma, and a confined environment with sufficient [[temperature]], [[pressure]], and confinement time. The combination of these parameters that results in a power-producing system is known as the [[Lawson criterion]]. In stellar cores the most common fuel is the lightest isotope of [[hydrogen]] ([[Protium (isotope)|protium]]), and [[gravity]] provides the conditions needed for fusion energy production. Proposed fusion reactors would use the heavy [[hydrogen isotope]]s of [[deuterium]] and [[tritium]] for [[DT fusion]], for which the Lawson criterion is known to be easiest to achieve. This produces a [[helium]] nucleus and an energetic [[neutron]].<ref>{{cite news |title=Fuelling the fusion reaction |url=https://www.iter.org/sci/FusionFuels |newspaper=Iter |access-date=23 June 2024}}</ref> Most designs aim to heat their fuel to around 100 million kelvins, which presents a major challenge in producing a successful design. Fusion fuel is 10 million times more energy dense than coal,<ref name="c286">{{cite web |date=2025-02-22 |title=Fusion Energy – Energy Singularity |url=https://www.energysingularity.cn/en/fusion-power/ |access-date=2025-02-22 |website=energysingularity.cn |language=zh}}</ref> but [[tritium]] is extremely rare on Earth, having a half life of only ~12.3 years. Consequently, during the operation of envisioned fusion reactors, [[breeding blanket]]s are subjected to [[neutron]] fluxes to generate tritium to complete the fuel cycle.<ref>{{cite journal |last1=Gan |first1=Y |last2=Hernandez |first2=F |last3=et |first3=al |title=Thermal Discrete Element Analysis of EU Solid Breeder Blanket Subjected to Neutron Irradiation |journal=Fusion Science and Technology |date=2017 |volume=66 |issue=1 |pages=83–90 |doi=10.13182/FST13-727 |arxiv=1406.4199 |url=https://hal.science/hal-02356062v1/file/1406.4199.pdf}}</ref> 

As a source of power, nuclear fusion has a number of potential advantages compared to [[nuclear fission|fission]]. These include little [[high-level waste]], and increased safety. However, the necessary combination of temperature, pressure, and duration has proven to be difficult to produce in a practical and economical manner. A second issue that affects common reactions is managing resulting [[neutron radiation]], which over time degrade the reaction chamber, especially the [[first wall]].

Fusion researchers have investigated various confinement concepts. The early emphasis was on three main systems: [[z-pinch]], [[stellarator]], and [[magnetic mirror]]. The current leading designs are the [[tokamak]] and [[inertial confinement fusion|inertial confinement]] (ICF) by [[laser]]. Both designs are under research at very large scales, most notably the [[ITER]] tokamak in France and the [[National Ignition Facility]] (NIF) laser in the United States. Researchers are also studying other designs that may offer less expensive approaches. Among these alternatives, there is increasing interest in [[magnetized target fusion]] and [[inertial electrostatic confinement]], and new variations of the stellarator.

{{Toclimit}}

== Background ==
{{main|Nuclear fusion}}
[[File:Sun in X-Ray.png|thumb|upright=1|The [[Sun]], like other [[star]]s, is a natural fusion reactor, where [[stellar nucleosynthesis]] transforms lighter elements into heavier elements with the release of energy.]]
[[File:Binding energy curve - common isotopes.svg|thumb|upright=2|[[Binding energy]] for different [[atomic nucleus|atomic nuclei]]. Iron-56 has the highest, making it the most stable. Nuclei to the left are likely to release energy when they fuse ([[nuclear fusion|fusion]]); those to the far right are likely to be unstable and release energy when they split ([[nuclear fission|fission]]).]]

=== Mechanism ===
Fusion reactions occur when two or more atomic nuclei come close enough for long enough that the [[nuclear force]] pulling them together exceeds the [[electrostatic force]] pushing them apart, fusing them into heavier nuclei. For nuclei heavier than [[iron-56]], the reaction is [[endothermic]], requiring an input of energy.<ref>{{cite web|url=http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html#c2|title=Fission and fusion can yield energy|publisher=Hyperphysics.phy-astr.gsu.edu|access-date=30 October 2014}}</ref> The heavy nuclei bigger than iron have many more protons resulting in a greater repulsive force. For nuclei lighter than iron-56, the reaction is [[exothermic]], releasing energy when they fuse. Since hydrogen has a single [[proton]] in its nucleus, it requires the least effort to attain fusion, and yields the most net energy output. Also since it has one electron, hydrogen is the easiest fuel to fully ionize.

The repulsive electrostatic interaction between nuclei operates across larger distances than the strong force, which has a range of roughly one [[femtometer]]—the diameter of a proton or neutron. The fuel atoms must be supplied enough kinetic energy to approach one another closely enough for the strong force to overcome the electrostatic repulsion in order to initiate fusion. The "[[Coulomb barrier]]" is the quantity of [[kinetic energy]] required to move the fuel atoms near enough. Atoms can be heated to extremely high temperatures or accelerated in a particle accelerator to produce this energy.

An atom loses its electrons once it is heated past its [[ionization energy]]. An [[ion]] is the name for the resultant bare nucleus. The result of this ionization is plasma, which is a heated cloud of ions and free electrons that were formerly bound to them. Plasmas are [[electrically conducting]] and magnetically controlled because the charges are separated. This is used by several fusion devices to confine the hot particles.

=== Cross section ===
[[File:Fusion rxnrate.svg|right|upright=1.5|thumb|The fusion reaction rate increases rapidly with temperature until it maximizes and then gradually drops off. The deuterium-tritium (D-T) fusion rate peaks at a lower temperature (about 70&nbsp;keV, or 800 million kelvin) and at a higher value than other reactions commonly considered for fusion energy.]]

A reaction's [[cross section (physics)|cross section]], denoted σ, measures the probability that a fusion reaction will happen. This depends on the relative velocity of the two nuclei. Higher relative velocities generally increase the probability, but the probability begins to decrease again at very high energies.<ref name="osti.gov">{{cite report |url=https://digital.library.unt.edu/ark:/67531/metadc872035/ |title=Fusion cross sections and reactivities |last1=Miley |first1=G. H. |last2=Towner |first2=H. |date=1974-06-17 |doi=10.2172/4014032 |osti=4014032 |last3=Ivich |first3=N. |type=Technical Report |via=Osti.gov|doi-access=free }}</ref>

In a plasma, particle velocity can be characterized using a [[probability distribution]]. If the plasma is [[Thermalisation|thermalized]], the distribution looks like a [[Gaussian curve]], or [[Maxwell–Boltzmann distribution]]. In this case, it is useful to use the average particle cross section over the velocity distribution. This is entered into the volumetric fusion rate:<ref name="Lawson">{{cite journal |last=Lawson |first=J. D. |date=1 December 1956 |title=Some Criteria for a Power Producing Thermonuclear Reactor |journal=Proceedings of the Physical Society. Section B |publisher=IOP Publishing |volume=70 |issue=1 |pages=6–10 |doi=10.1088/0370-1301/70/1/303 |bibcode=1957PPSB...70....6L |issn=0370-1301}}</ref>

:<math>P_\text{fusion} = n_A n_B \langle \sigma v_{A,B} \rangle E_\text{fusion}</math>

where:

* <math>P_\text{fusion}</math> is the energy made by fusion, per time and volume
* ''n'' is the number density of species A or B, of the particles in the volume
* <math>\langle \sigma v_{A,B} \rangle</math> is the cross section of that reaction, average over all the velocities of the two species ''v''
* <math>E_\text{fusion}</math> is the energy released by that fusion reaction.

=== Lawson criterion ===
The [[Lawson criterion]] considers the energy balance between the energy produced in fusion reactions to the energy being lost to the environment. In order to generate usable energy, a system would have to produce more energy than it loses. Lawson assumed an [[First law of thermodynamics|energy balance]], shown below.<ref name="Lawson"/>

:<math>P_\text{out} = \eta_\text{capture}\left(P_\text{fusion} - P_\text{conduction} - P_\text{radiation}\right)</math>
where:
* <math>P_\text{out}</math> is the net power from fusion
* <math>\eta_\text{capture}</math> is the efficiency of capturing the output of the fusion
* <math>P_\text{fusion}</math> is the rate of energy generated by the fusion reactions
* <math>P_\text{conduction}</math> is the conduction losses as energetic mass leaves the plasma
* <math>P_\text{radiation}</math> is the radiation losses as energy leaves as light and neutron flux.

The rate of fusion, and thus P<sub>fusion</sub>, depends on the temperature and density of the plasma. The plasma loses energy through [[Thermal conduction|conduction]] and [[radiation]].<ref name="Lawson"/> Conduction occurs when [[ion]]s, [[electron]]s, or [[neutral particle|neutrals]] impact other substances, typically a surface of the device, and transfer a portion of their kinetic energy to the other atoms. The rate of conduction is also based on the temperature and density. Radiation is energy that leaves the cloud as light. Radiation also increases with temperature as well as the mass of the ions. Fusion power systems must operate in a region where the rate of fusion is higher than the losses.

=== Triple product: density, temperature, time ===
[[File:Fusion Triples 2021.png|thumb|upright=2|alt=Fusion trapping (left) against temperature (bottom) for various fusion approaches as of 2021, assuming DT fuel. |Fusion trapping (left) against temperature (bottom) for various fusion approaches as of 2021, assuming DT fuel<ref>Wurzel, Samuel E., and Scott C. Hsu. "Progress toward fusion energy breakeven and gain as measured against the Lawson criterion." arXiv preprint arXiv:2105.10954 (2021).</ref> Solid line corresponds to Q = ∞ for IFC (inertial confinement fusion). Dashed line corresponds to Q = 0.01 for IFC. Colored contours correspond to Q factors for MFC (magnetic confinement fusion): Q = ∞ (brown), Q = 10 (red), Q = 2 (yellow), Q = 1 (green), Q = 0.1 (strong blue), Q = 0.01 (lighter blue), Q = 0.001 (even lighter blue), Q = 0.0001 (faint blue).]]
The [[Lawson criterion]] argues that a machine holding a thermalized and quasi-[[Neutral particle|neutral]] plasma has to generate enough energy to overcome its energy losses. The amount of energy released in a given volume is a function of the temperature, and thus the reaction rate on a per-particle basis, the density of particles within that volume, and finally the confinement time, the length of time that energy stays within the volume.<ref name="Lawson"/><ref>{{cite web |url=http://www.efda.org/2013/02/triple-product/ |title=Lawson's three criteria |publisher=EFDA |date=February 25, 2013 |access-date=2014-08-24 |archive-url=https://web.archive.org/web/20140911210243/http://www.efda.org/2013/02/triple-product/ |archive-date=2014-09-11 |url-status=dead }}</ref> This is known as the "triple product": the plasma density, temperature, and confinement time.<ref>{{cite web |url=http://www.efda.org/glossary/triple-product/ |title=Triple product |publisher=EFDA |date=2014-06-20 |access-date=2014-08-24 |archive-url=https://web.archive.org/web/20140911205015/http://www.efda.org/glossary/triple-product/ |archive-date=2014-09-11 |url-status=dead }}</ref>

In magnetic confinement, the density is low, on the order of a "good vacuum". For instance, in the [[ITER]] device the fuel density is about {{nowrap|1.0 × 10<sup>19</sup> m<sup>−3</sup>}}, which is about one-millionth atmospheric density.<ref>{{cite web |url=https://accelconf.web.cern.ch/e06/TALKS/FRYCPA01_TALK.PDF |title=ITER and the International ITER and the International Scientific Collaboration |first=Stefano |last=Chiocchio}}</ref> This means that the temperature and/or confinement time must increase. Fusion-relevant temperatures have been achieved using a variety of heating methods that were developed in the early 1970s. In modern machines, {{as of|2019|lc=yes}}, the major remaining issue was the confinement time. Plasmas in strong magnetic fields are subject to a number of inherent instabilities, which must be suppressed to reach useful durations. One way to do this is to simply make the reactor volume larger, which reduces the rate of leakage due to [[classical diffusion]]. This is why ITER is so large.

In contrast, inertial confinement systems approach useful triple product values via higher density, and have short confinement intervals. In [[National Ignition Facility|NIF]], the initial frozen hydrogen fuel load has a density less than water that is increased to about 100 times the density of lead. In these conditions, the rate of fusion is so high that the fuel fuses in the microseconds it takes for the heat generated by the reactions to blow the fuel apart. Although NIF is also large, this is a function of its "driver" design, not inherent to the fusion process.

=== Energy capture ===
Multiple approaches have been proposed to capture the energy that fusion produces. The simplest is to heat a fluid. The commonly targeted D-T reaction releases much of its energy as fast-moving neutrons. Electrically neutral, the neutron is unaffected by the confinement scheme. In most designs, it is captured in a thick "blanket" of [[lithium]] surrounding the reactor core. When struck by a high-energy neutron, the blanket heats up. It is then actively cooled with a working fluid that drives a turbine to produce power.

Another design proposed to use the neutrons to breed fission fuel in a blanket of [[nuclear waste]], a concept known as a [[fission-fusion hybrid]]. In these systems, the power output is enhanced by the fission events, and power is extracted using systems like those in conventional fission reactors.<ref>{{cite web|url=https://life.llnl.gov/ |title=Laser Inertial Fusion Energy |publisher=Life.llnl.gov |access-date=2014-08-24 |url-status=dead |archive-url=https://web.archive.org/web/20140915170021/https://life.llnl.gov/ |archive-date=2014-09-15 }}</ref>

Designs that use other fuels, notably the proton-boron [[aneutronic fusion]] reaction, release much more of their energy in the form of charged particles. In these cases, power extraction systems based on the movement of these charges are possible. [[Direct energy conversion]] was developed at [[Lawrence Livermore National Laboratory]] (LLNL) in the 1980s as a method to maintain a voltage directly using fusion reaction products. This has demonstrated energy capture efficiency of 48 percent.<ref name="ReferenceA">{{cite journal | last1=Barr | first1=W. L. | last2=Moir | first2=R. W. | last3=Hamilton | first3=G. W. | title=Experimental results from a beam direct converter at 100 kV | journal=Journal of Fusion Energy | publisher=Springer Science and Business Media LLC | volume=2 | issue=2 | year=1982 | issn=0164-0313 | doi=10.1007/bf01054580 | pages=131–143| bibcode=1982JFuE....2..131B | s2cid=120604056 }}</ref>

== Plasma behavior ==
Plasma is an ionized gas that conducts electricity.<ref>{{Cite book |last=Fitzpatrick |first=Richard |title=Plasma physics: an introduction |date=2014 |isbn=978-1466594265 |location=Boca Raton, Florida |publisher=CRC Press, Taylor & Francis Group |language=en-us |oclc=900866248}}</ref> In bulk, it is modeled using [[magnetohydrodynamics]], which is a combination of the [[Navier–Stokes equations]] governing fluids and [[Maxwell's equations]] governing how [[magnetic field|magnetic]] and [[electric field]]s behave.<ref>{{cite journal |last1=Alfvén |first1=H. |year=1942 |title=Existence of electromagnetic-hydrodynamic waves |journal=Nature |volume=150 |issue=3805 |pages=405–406 |bibcode=1942Natur.150..405A |doi=10.1038/150405d0 |s2cid=4072220}}</ref> Fusion exploits several plasma properties, including:
* Self-organizing plasma conducts electric and magnetic fields. Its motions generate fields that can in turn contain it.<ref>{{cite journal |last1=Tuszewski |first1=M. |year=1988 |title=Field reversed configurations |url=https://zenodo.org/record/1235740 |journal=Nuclear Fusion |type=Submitted manuscript |volume=28 |issue=11 |pages=2033–2092 |doi=10.1088/0029-5515/28/11/008 |s2cid=122791237|doi-access=free }}</ref>
* [[Diamagnetism|Diamagnetic plasma]] can generate its own internal magnetic field. This can reject an externally applied magnetic field, making it diamagnetic.<ref>{{Cite journal |last1=Sijoy |first1=C. D. |last2=Chaturvedi |first2=Shashank |date=2012 |title=An Eulerian MHD model for the analysis of magnetic flux compression by expanding diamagnetic fusion plasma sphere |url=http://dx.doi.org/10.1016/j.fusengdes.2011.10.012 |journal=Fusion Engineering and Design |volume=87 |issue=2 |pages=104–117 |doi=10.1016/j.fusengdes.2011.10.012 |bibcode=2012FusED..87..104S |issn=0920-3796}}</ref>
* [[Magnetic mirror]]s can reflect plasma when it moves from a low to high density field.<ref>{{Cite book |last=Post |first=R. F. |title=Proceedings of the second United Nations International Conference on the Peaceful Uses of Atomic Energy held in Geneva 1 September – 13 September 1958 |volume=32 |date=1958 |publisher=United Nations |editor-last=United Nations International Conference on the Peaceful Uses of Atomic Energy |location=Geneva, Switzerland |language=en |oclc=643589395}}</ref><sup>:24</sup>

== Methods ==
[[File:Chart of Fusion Approaches.png|thumb|upright=2|Approaches to fusion, in color coded families: Pinch Family (orange), Mirror Family (red), Cusp Systems (violet), Tokamaks & Stellarators (Green), Plasma Structures (gray), Inertial Electrostatic Confinement (dark yellow), Inertial Confinement Fusion (ICF, blue), Plasma Jet Magneto Inertial Fusion (PJMIF, dark pink).]]

=== Magnetic confinement ===
{{Main|Magnetic confinement fusion}}
* [[Tokamak]]: the most well-developed and well-funded approach. This method drives hot plasma around in a magnetically confined [[torus]], with an internal current. When completed, ITER will become the world's largest tokamak. As of September 2018 an estimated 226 experimental tokamaks were either planned, decommissioned or operating (50) worldwide.<ref>{{Cite web|title=All-the-Worlds-Tokamaks|url=http://www.tokamak.info/|access-date=2020-10-11|website=www.tokamak.info}}</ref>
* [[Spherical tokamak]]: also known as spherical torus. A variation on the tokamak with a spherical shape.
* [[Stellarator]]: Twisted rings of hot plasma. The stellarator attempts to create a natural twisted plasma path, using external magnets. Stellarators were developed by [[Lyman Spitzer]] in 1950 and evolved into four designs: Torsatron, Heliotron, Heliac and Helias. One example is [[Wendelstein 7-X]], a German device. It is the world's largest stellarator.<ref>{{Cite web|title=The first plasma: the Wendelstein 7-X fusion device is now in operation|url=https://www.ipp.mpg.de/3984226/12_15|access-date=2020-10-11|website=www.ipp.mpg.de|language=en}}</ref>
* Internal rings: Stellarators create a twisted plasma using external magnets, while tokamaks do so using a current induced in the plasma. Several classes of designs provide this twist using conductors inside the plasma. Early calculations showed that collisions between the plasma and the supports for the conductors would remove energy faster than fusion reactions could replace it. Modern variations, including the [[Levitated dipole|Levitated Dipole Experiment (LDX)]], use a solid superconducting torus that is magnetically levitated inside the reactor chamber.<ref>{{Cite web|last=Chandler|first=David|title=MIT tests unique approach to fusion power|url=https://news.mit.edu/2008/ldx-tt0319|access-date=2020-10-11|website=MIT News {{!}} Massachusetts Institute of Technology|date=March 19, 2008 |language=en}}</ref>
* [[Magnetic mirror]]: Developed by [[Richard F. Post]] and teams at Lawrence Livermore National Laboratory ([[LLNL]]) in the 1960s.<ref name="Post 99–111">{{Citation|last=Post|first=R. F.|title=Mirror systems: fuel cycles, loss reduction and energy recovery|date=1970-01-01|url=https://www.icevirtuallibrary.com/doi/abs/10.1680/nfr.44661.0007|work=Nuclear fusion reactors|pages=99–111|series=Conference Proceedings|publisher=Thomas Telford Publishing|doi=10.1680/nfr.44661|isbn=978-0727744661|access-date=2020-10-11}}</ref> Magnetic mirrors reflect plasma back and forth in a line. Variations included the [[Tandem Mirror Experiment|Tandem Mirror]], magnetic bottle and the [[biconic cusp]].<ref>{{Cite book|last1=Berowitz|first1=J. L |title=Proceedings of the second United Nations International Conference on the Peaceful Uses of Atomic Energy |volume=31|last2=Grad|first2=H.|last3=Rubin|first3=H.|date=1958|publisher=United Nations|location=Geneva|language=en|oclc=840480538}}</ref> A series of mirror machines were built by the US government in the 1970s and 1980s, principally at LLNL.<ref>{{cite journal | last1=Bagryansky | first1=P. A. | last2=Shalashov | first2=A. G. | last3=Gospodchikov | first3=E. D. | last4=Lizunov | first4=A. A. | last5=Maximov | first5=V. V. | last6=Prikhodko | first6=V. V. | last7=Soldatkina | first7=E. I. | last8=Solomakhin | first8=A. L. | last9=Yakovlev | first9=D. V. | title=Threefold Increase of the Bulk Electron Temperature of Plasma Discharges in a Magnetic Mirror Device | journal=Physical Review Letters | volume=114 | issue=20 | date=18 May 2015 | issn=0031-9007 | doi=10.1103/physrevlett.114.205001 | pmid=26047233 | page=205001| arxiv=1411.6288 | bibcode=2015PhRvL.114t5001B | s2cid=118484958 }}</ref> However, calculations in the 1970s estimated it was unlikely these would ever be commercially useful.
* [[Bumpy torus]]: A number of magnetic mirrors are arranged end-to-end in a toroidal ring. Any fuel ions that leak out of one are confined in a neighboring mirror, permitting the plasma pressure to be raised arbitrarily high without loss. An experimental facility, the ELMO Bumpy Torus or EBT was built and tested at [[Oak Ridge National Laboratory]] (ORNL) in the 1970s.
* [[Field-reversed configuration]]: This device traps plasma in a self-organized quasi-stable structure; where the particle motion makes an internal magnetic field which then traps itself.<ref name="Freidberg2007">{{cite book|first=Jeffrey P. |last=Freidberg|title=Plasma Physics and Fusion Energy|url={{google books |plainurl=y |id=ZGU-ngEACAAJ}}|date= 2007|publisher=Cambridge University Press|isbn=978-0521851077}}</ref>
* [[Spheromak]]: Similar to a field-reversed configuration, a semi-stable plasma structure made by using the plasmas' self-generated magnetic field. A spheromak has both toroidal and poloidal fields, while a field-reversed configuration has no toroidal field.<ref>{{cite book |title=Magnetic Fusion Technology |publisher=Springer London |year=2013 |isbn=978-1447155553 |editor-last=Dolan |editor-first=Thomas J. |series=Lecture Notes in Energy |volume=19 |location=London, England |pages=30–40 |language=en |doi=10.1007/978-1-4471-5556-0 |issn=2195-1284 }}</ref>
* [[Dynomak]] is a spheromak that is formed and sustained using continuous [[magnetic flux]] injection.<ref>D. A. Sutherland, T. R. Jarboe et al., "The dynomak: An advanced spheromak reactor concept with imposed-dynamo current drive and next-generation nuclear power technologies", Fusion Engineering and Design, Volume 89, Issue 4, April 2014, pp. 412–425.</ref><ref>Jarboe, T. R., et al. "Spheromak formation by steady inductive helicity injection." Physical Review Letters 97.11 (2006): 115003</ref><ref>Jarboe, T. R., et al. "Recent results from the HIT-SI experiment." Nuclear Fusion 51.6 (2011): 063029</ref> 
* [[Reversed field pinch]]: Here the plasma moves inside a ring. It has an internal magnetic field. Moving out from the center of this ring, the magnetic field reverses direction.

=== Inertial confinement ===
{{Main|Inertial confinement fusion}}
[[File:NIF output over 11 years without legend.png|upright=1.7|thumb|alt=Plot of NIF results from 2012 to 2022|Plot of NIF results from 2012 to 2022]]

* Indirect drive: Lasers heat a structure known as a [[Hohlraum]] that becomes so hot it begins to radiate [[x-ray]] light. These x-rays heat a fuel pellet, causing it to collapse inward to compress the fuel. The largest system using this method is the [[National Ignition Facility]], followed closely by [[Laser Mégajoule]].<ref name="Nuckolls, John 1972">{{cite journal | last1 = Nuckolls | first1 = John | last2 = Wood | first2 = Lowell | last3 = Thiessen | first3 = Albert | last4 = Zimmerman | first4 = George | s2cid = 45684425 | year = 1972 | title = Laser Compression of Matter to Super-High Densities: Thermonuclear (CTR) Applications | journal = Nature | volume = 239 | issue = 5368| pages = 139–142 | doi = 10.1038/239139a0 |bibcode = 1972Natur.239..139N }}</ref>
* Direct drive: Lasers directly heat the fuel pellet. Notable direct drive experiments have been conducted at the [[Laboratory for Laser Energetics]] (LLE) and the [[GEKKO XII]] facilities. Good implosions require fuel pellets with close to a perfect shape in order to generate a symmetrical inward [[shock wave]] that produces the high-density plasma.{{citation needed|date=August 2023}}
* Fast ignition: This method uses two laser blasts. The first blast compresses the fusion fuel, while the second ignites it. {{as of|2019}} this technique had lost favor for energy production.<ref>{{Cite book|last=Turrell|first=Arthur |title=How to Build a Star: the science of nuclear fusion and the quest to harness its power|date=2021|publisher=Weidenfeld & Nicolson |isbn=978-1474611596|location=Place of publication not identified|language=en|oclc=1048447399}}</ref>
* [[Magneto-inertial fusion]] or [[Magnetized Liner Inertial Fusion]]: This combines a laser pulse with a magnetic pinch. The pinch community refers to it as magnetized liner inertial fusion while the ICF community refers to it as magneto-inertial fusion.<ref name="IFSA2007">{{cite journal |last=Thio |first=Y. C. F. |date=1 April 2008 |title=Status of the US program in magneto-inertial fusion |journal=Journal of Physics: Conference Series |publisher=IOP Publishing |volume=112 |issue=4 |page=042084 |bibcode=2008JPhCS.112d2084T |doi=10.1088/1742-6596/112/4/042084 |issn=1742-6596 |doi-access=free}}</ref>
* Ion Beams: Ion beams replace laser beams to heat the fuel.<ref>{{cite conference |last1=Sharp |first1=W. M. |last2=Friedman |first2=A. |display-authors=1 |year=2011 |title=Inertial Fusion Driven by Intense Heavy-Ion Beams |url=https://accelconf.web.cern.ch/AccelConf/PAC2011/papers/weoas1.pdf |conference=Proceedings of 2011 Particle Accelerator Conference |location=New York, New York, USA |page=1386 |archive-url=https://web.archive.org/web/20171126054145/http://accelconf.web.cern.ch/AccelConf/PAC2011/papers/weoas1.pdf |archive-date=November 26, 2017 |access-date=August 3, 2019 |url-status=dead}}</ref> The main difference is that the beam has momentum due to mass, whereas lasers do not. As of 2019 it appears unlikely that ion beams can be sufficiently focused spatially and in time.
* [[Z Pulsed Power Facility|Z-machine]]: Sends an electric current through thin tungsten wires, heating them sufficiently to generate x-rays. Like the indirect drive approach, these x-rays then compress a fuel capsule.

=== Magnetic or electric pinches ===
{{Main|Pinch (plasma physics)}}

* ''[[Z-pinch]]:'' A current travels in the z-direction through the plasma. The current generates a magnetic field that compresses the plasma. Pinches were the first method for human-made controlled fusion.<ref name="Seife, Charles 2008">{{cite book |last=Seife |first=Charles |title=Sun in a bottle: the strange history of fusion and the science of wishful thinking |publisher=Viking |year=2008 |isbn=978-0670020331 |location=New York |language=en-us |oclc=213765956}}</ref><ref name="Phillips, James 2013">{{cite journal|last=Phillips|first=James|title=Magnetic Fusion|journal=Los Alamos Science|date=1983|pages=64–67|access-date=4 Apr 2013|url=https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-83-5080|archive-url=https://web.archive.org/web/20161223163131/http://permalink.lanl.gov/object/tr?what=info%3Alanl-repo%2Flareport%2FLA-UR-83-5080|archive-date=December 23, 2016|url-status=dead}}</ref> The z-pinch has inherent instabilities that limit its compression and heating to values too low for practical fusion. The largest such machine, the UK's [[ZETA (fusion reactor)|ZETA]], was the last major experiment of the sort. The problems in z-pinch led to the tokamak design. The [[dense plasma focus]] is a possibly superior variation.
* ''[[Theta-pinch]]:'' A current circles around the outside of a plasma column, in the theta direction. This induces a magnetic field running down the center of the plasma, as opposed to around it. The early theta-pinch device Scylla was the first to conclusively demonstrate fusion, but later work demonstrated it had inherent limits that made it uninteresting for power production.
* ''Sheared Flow Stabilized Z-Pinch:'' Research at the [[University of Washington]] under Uri Shumlak investigated the use of sheared-flow stabilization to smooth out the instabilities of Z-pinch reactors. This involves accelerating neutral gas along the axis of the pinch. Experimental machines included the FuZE and Zap Flow Z-Pinch experimental reactors.<ref>{{Cite web|date=2014-11-07|title=Flow Z-Pinch Experiments|url=https://www.aa.washington.edu/research/ZaP|access-date=2020-10-11|website=Aeronautics and Astronautics|language=en}}</ref> In 2017, British technology investor and entrepreneur [[Benj Conway]], together with physicists Brian Nelson and Uri Shumlak, co-founded Zap Energy to attempt to commercialize the technology for power production.<ref>{{cite web |url=https://www.zapenergyinc.com/ |publisher=Zap Energy |title=Zap Energy |access-date=February 13, 2020 |archive-url=https://web.archive.org/web/20200213065735/https://www.zapenergyinc.com/ |archive-date=February 13, 2020 |url-status=dead }}</ref><ref>{{Cite web|title=Board of Directors|url=https://www.zapenergyinc.com/board|access-date=2020-09-08|website=ZAP ENERGY|language=en-US}}</ref><ref>{{Cite web|date=2020-08-13|title=Chevron announces investment in nuclear fusion start-up Zap Energy|url=https://www.power-technology.com/news/chevron-announces-investment-nuclear-fusion-start-up-company-zap-energy/|access-date=2020-09-08|website=Power Technology {{!}} Energy News and Market Analysis|language=en-GB}}</ref>
* ''Screw Pinch:'' This method combines a theta and z-pinch for improved stabilization.<ref>{{cite journal | last1=Srivastava | first1=Krishna M. | last2=Vyas | first2=D. N. | title=Non-linear analysis of the stability of the Screw Pinch | journal=Astrophysics and Space Science | publisher=Springer Nature | volume=86 | issue=1 | year=1982 | issn=0004-640X | doi=10.1007/bf00651831 | pages=71–89| bibcode=1982Ap&SS..86...71S | s2cid=121575638 }}</ref>

=== Inertial electrostatic confinement ===
{{Main|Inertial electrostatic confinement}}

* ''[[Fusor]]:'' An electric field heats ions to fusion conditions. The machine typically uses two spherical cages, a cathode inside the anode, inside a vacuum. These machines are not considered a viable approach to net power because of their high [[Electrical conductor|conduction]] and [[radiation]] losses.<ref>{{cite journal | last=Rider | first=Todd H. | title=A general critique of inertial-electrostatic confinement fusion systems | journal=Physics of Plasmas | publisher=AIP Publishing | volume=2 | issue=6 | year=1995 | issn=1070-664X | doi=10.1063/1.871273 | pages=1853–1872| bibcode=1995PhPl....2.1853R | hdl=1721.1/29869 | s2cid=12336904 | hdl-access=free }}</ref> They are simple enough to build that amateurs have fused atoms using them.<ref>{{cite web | last=Clynes | first=Tom | title=The Boy Who Played With Fusion | website=Popular Science | date=14 February 2012 | url=https://www.popsci.com/science/article/2012-02/boy-who-played-fusion/ | access-date=3 August 2019}}</ref>
* ''[[Polywell]]:'' Attempts to combine magnetic confinement with electrostatic fields, to avoid the [[Electrical conductor|conduction]] losses generated by the cage.<ref>US patent 5,160,695, Robert W. Bussard, "Method and apparatus for creating and controlling nuclear fusion reactions", issued 1992-11-03</ref>

=== Other ===
* ''[[Magnetized target fusion]]:'' Confines hot plasma using a magnetic field and squeezes it using inertia. Examples include [[LANL]] FRX-L machine,<ref>{{Cite journal|last1=Taccetti|first1=J. M.|last2=Intrator|first2=T. P.|last3=Wurden|first3=G. A.|last4=Zhang|first4=S. Y.|last5=Aragonez|first5=R.|last6=Assmus|first6=P. N.|last7=Bass|first7=C. M.|last8=Carey|first8=C.|last9=deVries|first9=S. A.|last10=Fienup|first10=W. J.|last11=Furno|first11=I.|date=2003-09-25|title=FRX-L: A field-reversed configuration plasma injector for magnetized target fusion|url=https://aip.scitation.org/doi/10.1063/1.1606534|journal=Review of Scientific Instruments|volume=74|issue=10|pages=4314–4323|doi=10.1063/1.1606534|bibcode=2003RScI...74.4314T|issn=0034-6748}}</ref> [[General Fusion]] (piston compression with liquid metal liner), HyperJet Fusion (plasma jet compression with plasma liner).<ref>{{Cite journal|last1=Hsu|first1=S. C.|last2=Awe|first2=T. J.|last3=Brockington|first3=S.|last4=Case|first4=A.|last5=Cassibry|first5=J. T.|last6=Kagan|first6=G.|last7=Messer|first7=S. J.|last8=Stanic|first8=M.|last9=Tang|first9=X.|last10=Welch|first10=D. R.|last11=Witherspoon|first11=F. D.|date=2012|title=Spherically Imploding Plasma Liners as a Standoff Driver for Magnetoinertial Fusion|url=https://ieeexplore.ieee.org/document/6168279/?denied=|journal=IEEE Transactions on Plasma Science|volume=40|issue=5|pages=1287–1298|doi=10.1109/TPS.2012.2186829|bibcode=2012ITPS...40.1287H|s2cid=32998378|issn=1939-9375}}</ref><ref name=5big/>
* ''Uncontrolled:'' Fusion has been initiated by man, using uncontrolled fission explosions to stimulate fusion. Early proposals for fusion power included using bombs to initiate reactions. See [[Project PACER]].
* ''[[Colliding beam fusion]]:'' A beam of high energy particles fired at another beam or target can initiate fusion. This was used in the 1970s and 1980s to study the cross sections of fusion reactions.<ref name="osti.gov" /> However beam systems cannot be used for power because keeping a beam coherent takes more energy than comes from fusion.
* ''[[Muon-catalyzed fusion]]:'' This approach replaces [[electron]]s in [[diatomic molecule]]s of [[isotope]]s of [[hydrogen]] with [[muon]]s—more massive particles with the same [[electric charge]]. Their greater mass compresses the nuclei enough such that the [[strong interaction]] can cause fusion.{{sfn|Nagamine|2003}} As of 2007 producing muons required more energy than can be obtained from muon-catalyzed fusion.<ref>{{Cite book |last=Nagamine |first=K. |title=Introductory muon science |date=2007 |publisher=Cambridge University Press |isbn=978-0521038201 |location=Cambridge, England |language=en |oclc=124025585}}</ref>
* ''[[Lattice confinement fusion]]:'' Lattice confinement fusion ('''LCF''') is a type of [[nuclear fusion]] in which [[deuteron]]-saturated metals are exposed to [[gamma radiation]] or ion beams, such as in an [[Inertial electrostatic confinement|IEC fusor]], avoiding the confined high-temperature plasmas used in other methods of fusion.<ref>{{Cite web|url=https://spectrum.ieee.org/lattice-confinement-fusion|title=NASA's New Shortcut to Fusion Power|last1=Baramsai |first1=Bayardadrakh |last2=Benyo |first2=Theresa |last3=Forsley |first3=Lawrence |last4=Steinetz |first4=Bruce |date=February 27, 2022|website=IEEE Spectrum}}</ref><ref name="erbium">{{Cite journal|url=http://dx.doi.org/10.1103/PhysRevC.101.044610|title=Novel nuclear reactions observed in bremsstrahlung-irradiated deuterated metals|first1=Bruce M.|last1=Steinetz|first2=Theresa L.|last2=Benyo|first3=Arnon|last3=Chait|first4=Robert C.|last4=Hendricks|first5=Lawrence P.|last5=Forsley|first6=Bayarbadrakh|last6=Baramsai|first7=Philip B.|last7=Ugorowski|first8=Michael D.|last8=Becks|first9=Vladimir|last9=Pines|first10=Marianna|last10=Pines|first11=Richard E.|last11=Martin|first12=Nicholas|last12=Penney|first13=Gustave C.|last13=Fralick|first14=Carl E.|last14=Sandifer|date=April 20, 2020|journal=Physical Review C|volume=101|issue=4|pages=044610|via=APS|doi=10.1103/physrevc.101.044610|bibcode=2020PhRvC.101d4610S|s2cid=219083603}}</ref>

== Common tools ==
Many approaches, equipment, and mechanisms are employed across multiple projects to address fusion heating, measurement, and power production.<ref>{{Cite journal|date=1972|title=Plasma Physics|journal=Government Reports Announcements|volume=72|pages=194}}</ref>

=== Machine learning ===
A [[deep reinforcement learning]] system has been used to control a [[tokamak]]-based reactor.<ref>{{cite journal |last1=Degrave |first1=J. |last2=Felici |first2=F. |date=2022 |title=Magnetic control of tokamak plasmas through deep reinforcement learning |journal=Nature |volume=602 |issue=7897 |pages=414–419 |doi=10.1038/s41586-021-04301-9 |pmid=35173339 |pmc=8850200 |bibcode=2022Natur.602..414D |url=https://doi.org/10.1038/s41586-021-04301-9 |access-date=2025-02-05}}</ref> The system was able to manipulate the magnetic coils to manage the plasma. The system was able to continuously adjust to maintain appropriate behavior (more complex than step-based systems).{{cn|date=July 2024}} In 2014, Google began working with California-based fusion company [[TAE Technologies]] to control the [[Joint European Torus]] (JET) to predict plasma behavior.<ref>{{Cite magazine|last=Katwala|first=Amit|date=February 16, 2022|title=DeepMind Has Trained an AI to Control Nuclear Fusion|language=en-US|magazine=Wired|url=https://www.wired.com/story/deepmind-ai-nuclear-fusion/|access-date=2022-02-17|issn=1059-1028}}</ref> [[DeepMind]] has also developed a control scheme with [[Tokamak à configuration variable|TCV]].<ref>{{cite magazine | url=https://www.wired.com/story/deepmind-ai-nuclear-fusion/ | title=DeepMind Has Trained an AI to Control Nuclear Fusion | magazine=Wired | last1=Katwala | first1=Amit }}</ref>

=== Heating ===
{{Main|Dielectric heating|Magnetic reconnection|Inertial electrostatic confinement|Neutral beam injection}}

* Electrostatic heating: an electric field can do [[work (thermodynamics)|work]] on charged ions or electrons, heating them.<ref>{{Cite book|last=Miley, George H. |title=Inertial electrostatic confinement (IEC) fusion : fundamentals and applications|date=2013|publisher=Springer|others=Murali, S. Krupakar|isbn=978-1461493389|location=Dordrecht|oclc=878605320}}</ref>
* [[Neutral-beam injection|Neutral beam injection]]: hydrogen is ionized and accelerated by an electric field to form a charged beam that is shone through a source of neutral hydrogen gas towards the plasma which itself is ionized and contained by a magnetic field. Some of the intermediate hydrogen gas is accelerated towards the plasma by collisions with the charged beam while remaining neutral: this neutral beam is thus unaffected by the magnetic field and so reaches the plasma. Once inside the plasma the neutral beam transmits energy to the plasma by collisions which ionize it and allow it to be contained by the magnetic field, thereby both heating and refueling the reactor in one operation. The remainder of the charged beam is diverted by magnetic fields onto cooled beam dumps.<ref>{{Cite book |last=Kunkel |first=W. B. |title=Fusion |publisher=Lawrence Livermore National Laboratory |year=1981 |isbn=978-0126852417 |editor-last=Teller |editor-first=E. |chapter=Neutral-beam injection}}</ref>
* Radio frequency heating: a radio wave causes the plasma to oscillate (i.e., [[microwave oven]]). This is also known as [[electron cyclotron resonance heating]], using for example [[gyrotron]]s, or [[dielectric heating]].<ref>{{Cite journal|last1=Erckmann|first1=V|last2=Gasparino|first2=U|date=1994-12-01|title=Electron cyclotron resonance heating and current drive in toroidal fusion plasmas|url=https://iopscience.iop.org/article/10.1088/0741-3335/36/12/001|journal=Plasma Physics and Controlled Fusion|volume=36|issue=12|pages=1869–1962|bibcode=1994PPCF...36.1869E|doi=10.1088/0741-3335/36/12/001|s2cid=250897078|issn=0741-3335}}</ref>
* [[Magnetic reconnection]]: when plasma gets dense, its electromagnetic properties can change, which can lead to [[magnetic reconnection]]. Reconnection helps fusion because it instantly dumps energy into a plasma, heating it quickly. Up to 45% of the magnetic field energy can heat the ions.<ref>{{Cite journal|last1=Ono|first1=Y.|last2=Tanabe|first2=H.|last3=Yamada|first3=T.|last4=Gi|first4=K.|last5=Watanabe|first5=T.|last6=Ii|first6=T.|last7=Gryaznevich|first7=M.|last8=Scannell|first8=R.|last9=Conway|first9=N.|last10=Crowley|first10=B.|last11=Michael|first11=C.|date=2015-05-01|title=High power heating of magnetic reconnection in merging tokamak experiments|url=https://aip.scitation.org/doi/10.1063/1.4920944|journal=Physics of Plasmas|volume=22|issue=5|pages=055708|bibcode=2015PhPl...22e5708O|doi=10.1063/1.4920944|issn=1070-664X|hdl=1885/28549|hdl-access=free}}</ref><ref>{{Cite journal|last1=Yamada|first1=M.|last2=Chen|first2=L.-J.|last3=Yoo|first3=J.|last4=Wang|first4=S.|last5=Fox|first5=W.|last6=Jara-Almonte|first6=J.|last7=Ji|first7=H.|last8=Daughton|first8=W.|last9=Le|first9=A.|last10=Burch|first10=J.|last11=Giles|first11=B.|date=2018-12-06|title=The two-fluid dynamics and energetics of the asymmetric magnetic reconnection in laboratory and space plasmas|url= |journal=Nature Communications|language=en|volume=9|issue=1|pages=5223|bibcode=2018NatCo...9.5223Y|doi=10.1038/s41467-018-07680-2|issn=2041-1723|pmc=6283883|pmid=30523290}}</ref>
* Magnetic oscillations: varying electric currents can be supplied to magnetic coils that heat plasma confined within a magnetic wall.<ref>McGuire, Thomas. Heating Plasma for Fusion Power Using Magnetic Field Oscillations. Baker Botts LLP, assignee. Issued: 4/2/14, Patent 14/243,447. N.d. Print.</ref>
* Antiproton annihilation: [[antiproton]]s injected into a mass of fusion fuel can induce thermonuclear reactions. This possibility as a method of spacecraft propulsion, known as [[antimatter-catalyzed nuclear pulse propulsion]], was investigated at [[Pennsylvania State University]] in connection with the proposed [[AIMStar]] project.{{Citation needed|date=June 2021}}

=== Measurement ===
{{Main|Flux loop|Langmuir probe|Neutron detection|Thomson scattering|X-ray detector}}

The diagnostics of a fusion scientific reactor are extremely complex and varied.<ref>{{Citation|title=Towards a fusion reactor|work=Nuclear Fusion|year=2002|publisher=IOP Publishing Ltd|doi=10.1887/0750307056/b888c9|isbn=0750307056|doi-access=free}}</ref> The diagnostics required for a fusion power reactor will be various but less complicated than those of a scientific reactor as by the time of commercialization, many real-time feedback and control diagnostics will have been perfected. However, the operating environment of a commercial fusion reactor will be harsher for diagnostic systems than in a scientific reactor because continuous operations may involve higher plasma temperatures and higher levels of neutron irradiation. In many proposed approaches, commercialization will require the additional ability to measure and separate diverter gases, for example helium and impurities, and to monitor fuel breeding, for instance the state of a tritium breeding liquid lithium liner.<ref>{{Citation|last1=Pearson|first1=Richard J|title=Review of approaches to fusion energy|date=2020|url=http://dx.doi.org/10.1088/978-0-7503-2719-0ch2|work=Commercialising Fusion Energy|publisher=IOP Publishing|access-date=2021-12-12|last2=Takeda|first2=Shutaro|doi=10.1088/978-0-7503-2719-0ch2|isbn=978-0750327190|s2cid=234561187}}</ref> The following are some basic techniques.
* [[Flux loop]]: a loop of wire is inserted into the magnetic field. As the field passes through the loop, a current is made. The current measures the total magnetic flux through that loop. This has been used on the [[National Compact Stellarator Experiment]],<ref>{{Cite book|last1=Labik|first1=George|last2=Brown|first2=Tom|last3=Johnson|first3=Dave|last4=Pomphrey|first4=Neil|last5=Stratton|first5=Brentley|last6=Viola|first6=Michael|last7=Zarnstorff|first7=Michael|last8=Duco|first8=Mike|last9=Edwards|first9=John|last10=Cole|first10=Mike|last11=Lazarus|first11=Ed|title=2007 IEEE 22nd Symposium on Fusion Engineering |chapter=National Compact Stellarator Experiment Vacuum Vessel External Flux Loops Design and Installation |date=2007|chapter-url=https://ieeexplore.ieee.org/document/4337935|pages=1–3|doi=10.1109/FUSION.2007.4337935|isbn=978-1424411931|s2cid=9298179}}</ref> the [[polywell]],<ref>{{Cite journal|last1=Park|first1=Jaeyoung|last2=Krall|first2=Nicholas A.|last3=Sieck|first3=Paul E.|last4=Offermann|first4=Dustin T.|last5=Skillicorn|first5=Michael|last6=Sanchez|first6=Andrew|last7=Davis|first7=Kevin|last8=Alderson|first8=Eric|last9=Lapenta|first9=Giovanni|date=2014-06-01|title=High Energy Electron Confinement in a Magnetic Cusp Configuration|journal=Physical Review X|volume=5|issue=2|pages=021024|arxiv=1406.0133|bibcode=2015PhRvX...5b1024P|doi=10.1103/PhysRevX.5.021024|s2cid=118478508}}</ref> and the [[Levitated dipole|LDX]] machines. A [[Langmuir probe]], a metal object placed in a plasma, can be employed. A potential is applied to it, giving it a [[voltage]] against the surrounding plasma. The metal collects charged particles, drawing a current. As the voltage changes, the current changes. This makes an [[Current–voltage characteristic|IV Curve]]. The IV-curve can be used to determine the local plasma density, potential and temperature.<ref>{{cite journal|last1=Mott-Smith|first1=H. M.|last2=Langmuir|first2=Irving|date=1 September 1926|title=The Theory of Collectors in Gaseous Discharges|journal=Physical Review|publisher=American Physical Society (APS)|volume=28|issue=4|pages=727–763|bibcode=1926PhRv...28..727M|doi=10.1103/physrev.28.727|issn=0031-899X}}</ref>
* [[Thomson scattering]]: "Light scatters" from plasma can be used to reconstruct plasma behavior, including density and temperature. It is common in [[Inertial confinement fusion]],<ref>{{cite journal | last1=Esarey | first1=Eric | last2=Ride | first2=Sally K. | last3=Sprangle | first3=Phillip | title=Nonlinear Thomson scattering of intense laser pulses from beams and plasmas | journal=Physical Review E | publisher=American Physical Society (APS) | volume=48 | issue=4 | date=1 September 1993 | issn=1063-651X | doi=10.1103/physreve.48.3003 | pmid=9960936 | pages=3003–3021| bibcode=1993PhRvE..48.3003E }}</ref> [[Tokamak]]s,<ref>{{Cite journal |last1=Kantor |first1=M. Yu |last2=Donné |first2=A. J. H. |last3=Jaspers |first3=R. |last4=van der Meiden |first4=H. J. |date=2009-02-26 |title=Thomson scattering system on the TEXTOR tokamak using a multi-pass laser beam configuration |url=https://iopscience.iop.org/article/10.1088/0741-3335/51/5/055002 |journal=Plasma Physics and Controlled Fusion |language=en |volume=51 |issue=5 |pages=055002 |bibcode=2009PPCF...51e5002K |doi=10.1088/0741-3335/51/5/055002 |issn=0741-3335 |s2cid=123495440}}</ref> and [[fusor]]s. In ICF systems, firing a second beam into a gold foil adjacent to the target makes x-rays that traverse the plasma. In tokamaks, this can be done using mirrors and detectors to reflect light.
* [[Neutron detection|Neutron detectors]]: [[Neutron detection#Types of neutron detectors|Several types of neutron detectors]] can record the rate at which neutrons are produced.<ref>{{Cite book|last=Tsoulfanidis|first=Nicholas|url=http://archive.org/details/measurementdetec00tsou|title=Measurement and detection of radiation|date=1995|publisher=Washington, DC : Taylor & Francis|others=Library Genesis|isbn=978-1560323174}}</ref><ref>{{Cite book|last=Knoll, Glenn F. |title=Radiation detection and measurement|date=2010|publisher=John Wiley|isbn=978-0470131480|edition=4th|location=Hoboken, NJ|oclc=612350364}}</ref>
* [[X-ray detectors]] Visible, IR, UV, and X-rays are emitted anytime a particle changes velocity.<ref>{{Cite journal|last=Larmor|first=Joseph|date=1897-01-01|title=IX. A dynamical theory of the electric and luminiferous medium. Part III. relations with material media|journal=Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character|volume=190|pages=205–300|doi=10.1098/rsta.1897.0020|bibcode=1897RSPTA.190..205L|doi-access=free}}</ref> If the reason is deflection by a magnetic field, the radiation is [[cyclotron]] radiation at low speeds and [[synchrotron]] radiation at high speeds. If the reason is deflection by another particle, plasma radiates X-rays, known as [[Bremsstrahlung]] radiation.<ref>{{Cite book |title=Diagnostics for experimental thermonuclear fusion reactors 2|date=1998|publisher=Springer |veditors=Stott PE, Gorini G, Prandoni P, Sindoni E |isbn=978-1461553533|location=New York|oclc=828735433}}</ref>

=== Power production ===
Neutron blankets absorb neutrons, which heats the blanket. Power can be extracted from the blanket in various ways:

* [[Steam turbine]]s can be driven by heat transferred into a [[working fluid]] that turns into steam, driving electric generators.<ref>{{Cite journal|last1=Ishiyama|first1=Shintaro|last2=Muto|first2=Yasushi|last3=Kato|first3=Yasuyoshi|last4=Nishio|first4=Satoshi|last5=Hayashi|first5=Takumi|last6=Nomoto|first6=Yasunobu|date=2008-03-01|title=Study of steam, helium and supercritical CO2 turbine power generations in prototype fusion power reactor|url=http://www.sciencedirect.com/science/article/pii/S0149197007001552|journal=Progress in Nuclear Energy |language=en|volume=50|issue=2|pages=325–332|doi=10.1016/j.pnucene.2007.11.078|issn=0149-1970}}</ref>
* Neutron blankets: These neutrons can regenerate spent fission fuel.<ref>{{cite web |last1=Anklam |first1=T. |last2=Simon |first2=A. J. |last3=Powers |first3=S. |last4=Meier |first4=W. R. |date=December 2, 2010 |title=LIFE: The Case for Early Commercialization of Fusion Energy |url=https://e-reports-ext.llnl.gov/pdf/459730.pdf |url-status=dead |archive-url=https://web.archive.org/web/20150904055903/https://e-reports-ext.llnl.gov/pdf/459730.pdf |archive-date=4 September 2015 |access-date=30 October 2014 |publisher=Lawrence Livermore National Laboratory, LLNL-JRNL-463536}}</ref> Tritium can be produced using a breeder blanket of liquid lithium or a helium cooled pebble bed made of lithium-bearing ceramic pebbles.<ref name="l2s">{{cite journal |last1=Hanaor |first1=D. A. H. |last2=Kolb |first2=M. H. H. |last3=Gan |first3=Y. |last4=Kamlah |first4=M. |last5=Knitter |first5=R. |year=2014 |title=Solution based synthesis of mixed-phase materials in the Li<sub>2</sub>TiO<sub>3</sub>-Li<sub>4</sub>SiO<sub>4</sub> system |journal=Journal of Nuclear Materials |volume=456 |pages=151–161 |arxiv=1410.7128 |bibcode=2015JNuM..456..151H |doi=10.1016/j.jnucmat.2014.09.028 |s2cid=94426898}}</ref>
* [[Direct energy conversion|Direct conversion]]: The [[kinetic energy]] of a particle can be converted into [[voltage]].<ref name="Post 99–111" /> It was first suggested by [[Richard F. Post]] in conjunction with [[magnetic mirror]]s, in the late 1960s. It has been proposed for [[Field-Reversed Configuration]]s as well as [[Dense Plasma Focus]] devices. The process converts a large fraction of the random energy of the fusion products into directed motion. The particles are then collected on electrodes at various large electrical potentials. This method has demonstrated an experimental efficiency of 48 percent.<ref>{{Cite journal|last1=Barr|first1=William L.|last2=Moir|first2=Ralph W.|date=1983-01-01|title=Test Results on Plasma Direct Converters|url=https://doi.org/10.13182/FST83-A20820|journal=Nuclear Technology – Fusion|volume=3|issue=1|pages=98–111|doi=10.13182/FST83-A20820|bibcode=1983NucTF...3...98B |issn=0272-3921}}</ref>
* [[Traveling-wave tube]]s pass charged helium atoms at several megavolts and just coming off the fusion reaction through a tube with a coil of wire around the outside. This passing charge at high voltage pulls electricity through the wire.

=== Confinement ===
[[File:IFE and MFE parameter space.svg|thumb|upright=1.75|Parameter space occupied by [[inertial fusion energy]] and [[magnetic fusion energy]] devices as of the mid-1990s. The regime allowing thermonuclear ignition with high gain lies near the upper right corner of the plot.]]

Confinement refers to all the conditions necessary to keep a plasma dense and hot long enough to undergo fusion. General principles:

* [[Mechanical equilibrium|Equilibrium]]: The forces acting on the plasma must be balanced. One exception is [[inertial confinement fusion|inertial confinement]], where the fusion must occur faster than the dispersal time.
* [[Plasma stability|Stability]]: The plasma must be constructed so that disturbances will not lead to the plasma dispersing.
* Transport or [[conduction (heat)|conduction]]: The loss of material must be sufficiently slow.<ref name="Lawson"/> The plasma carries energy off with it, so rapid loss of material will disrupt fusion. Material can be lost by transport into different regions or [[conduction (heat)|conduction]] through a solid or liquid.

To produce self-sustaining fusion, part of the energy released by the reaction must be used to heat new reactants and maintain the conditions for fusion.

==== Magnetic confinement ====
===== Magnetic Mirror =====
[[Magnetic mirror]] effect. If a particle follows the field line and enters a region of higher field strength, the particles can be reflected. Several devices apply this effect. The most famous was the magnetic mirror machines, a series of devices built at LLNL from the 1960s to the 1980s.<ref name=Booth>{{cite journal|last=Booth|first=William|title=Fusion's $372-Million Mothball|journal=Science|date=9 Oct 1987|volume=238|issue=4824|pages=152–155|doi= 10.1126/science.238.4824.152|pmid=17800453|bibcode=1987Sci...238..152B}}</ref> Other examples include magnetic bottles and [[Biconic cusp]].<ref>{{Cite book|last=Grad|first=Harold |title=Containment in cusped plasma systems (classic reprint).|date=2016|publisher=Forgotten Books |isbn=978-1333477035|location=<!-- Place of publication not identified -->|language=en|oclc=980257709}}</ref> Because the mirror machines were straight, they had some advantages over ring-shaped designs. The mirrors were easier to construct and maintain and [[Direct energy conversion|direct conversion]] energy capture was easier to implement.<ref name="ReferenceA"/> Poor confinement has led this approach to be abandoned, except in the polywell design.<ref>{{Cite web|last=Lee|first=Chris|date=2015-06-22|title=Magnetic mirror holds promise for fusion|url=https://arstechnica.com/science/2015/06/magnetic-mirror-holds-promise-for-fusion/|access-date=2020-10-11|website=Ars Technica|language=en-us}}</ref>

===== Magnetic loops =====
Magnetic loops bend the field lines back on themselves, either in circles or more commonly in nested [[torus|toroidal]] surfaces. The most highly developed systems of this type are the [[tokamak]], the stellarator, and the reversed field pinch. [[Compact toroid]]s, especially the field-reversed configuration and the spheromak, attempt to combine the advantages of toroidal magnetic surfaces with those of a [[simply connected space|simply connected]] (non-toroidal) machine, resulting in a mechanically simpler and smaller confinement area.

==== Inertial confinement ====
[[File:Electra Laser Generates 90K Shots.webm|thumb|alt=The Electra Laser at Naval Research Laboratory demonstrates 90,000 shots in 10 hours, repetition needed for IFE power plant.|The Electra Laser at Naval Research Laboratory demonstrates 90,000 shots in 10 hours, repetition needed for IFE power plant.]]

Inertial confinement is the use of rapid implosion to heat and confine plasma. A shell surrounding the fuel is imploded using a direct laser blast (direct drive), a secondary x-ray blast (indirect drive), or heavy beams. The fuel must be compressed to about 30 times solid density with energetic beams. Direct drive can in principle be efficient, but insufficient uniformity has prevented success.<ref name="confinement">{{Cite book|last=Pfalzner, Susanne |title=An introduction to inertial confinement fusion|date=2006|publisher=Taylor & Francis/CRC Press|isbn=1420011847|location=New York|oclc=72564680}}</ref><sup>:19–20</sup> Indirect drive uses beams to heat a shell, driving the shell to radiate [[x-rays]], which then implode the pellet. The beams are commonly laser beams, but ion and electron beams have been investigated.<ref name="confinement" /><sup>:182–193</sup>

===== Electrostatic confinement =====
[[Inertial electrostatic confinement|Electrostatic confinement fusion]] devices use electrostatic fields. The best known is the [[fusor]]. This device has a cathode inside an anode wire cage. Positive ions fly towards the negative inner cage, and are heated by the electric field in the process. If they miss the inner cage they can collide and fuse. Ions typically hit the cathode, however, creating prohibitory high [[conduction (heat)|conduction]] losses. Fusion rates in [[fusor]]s are low because of competing physical effects, such as energy loss in the form of light radiation.<ref name="Thorson1996">{{cite book|first=Timothy A. |last=Thorson|title=Ion flow and fusion reactivity characterization of a spherically convergent ion focus|url={{google books |plainurl=y |id=k6zVAAAAMAAJ}}|year=1996|publisher=University of Wisconsin, Madison}}</ref> Designs have been proposed to avoid the problems associated with the cage, by generating the field using a non-neutral cloud. These include a plasma oscillating device,<ref>{{Cite journal|last1=Barnes|first1=D. C.|last2=Nebel|first2=R. A.|date=July 1998|title=Stable, thermal equilibrium, large-amplitude, spherical plasma oscillations in electrostatic confinement devices|url=http://dx.doi.org/10.1063/1.872933|journal=Physics of Plasmas|volume=5|issue=7|pages=2498–2503|doi=10.1063/1.872933|bibcode=1998PhPl....5.2498B|issn=1070-664X}}</ref> a magnetically shielded-grid,<ref>{{Cite journal|last1=Hedditch|first1=John|last2=Bowden-Reid|first2=Richard|last3=Khachan|first3=Joe|date=October 2015|title=Fusion in a magnetically-shielded-grid inertial electrostatic confinement device|journal=Physics of Plasmas|volume=22|issue=10|pages=102705|doi=10.1063/1.4933213|issn=1070-664X|arxiv=1510.01788|bibcode=2015PhPl...22j2705H }}</ref> a [[penning trap]], the [[polywell]],<ref>{{cite journal | last1 = Carr | first1 = M. | last2 = Khachan | first2 = J. | year = 2013 | title = A biased probe analysis of potential well formation in an electron only, low beta Polywell magnetic field | url = https://zenodo.org/record/1244056| journal = Physics of Plasmas | volume = 20 | issue = 5| page = 052504 | doi = 10.1063/1.4804279 | bibcode = 2013PhPl...20e2504C }}</ref> and the F1 cathode driver concept.<ref>{{Cite book|last1=Sieckand|first1=Paul|url=https://arpa-e.energy.gov/sites/default/files/3_VOLBERG.pdf|title=Fusion One Corporation|last2=Volberg|first2=Randall|publisher=Fusion One Corporation|year=2017}}</ref>

== Fuels ==
The fuels considered for fusion power have all been light elements like the isotopes of hydrogen—[[Isotopes of hydrogen#Hydrogen-1 (Protium)|protium]], [[deuterium]], and [[tritium]].<ref name="osti.gov"/> The deuterium and [[helium-3]] reaction requires helium-3, an isotope of helium so scarce on Earth that it would have to be [[Asteroid mining|mined extraterrestrially]] or produced by other nuclear reactions. Ultimately, researchers hope to adopt the protium–boron-11 reaction, because it does not directly produce neutrons, although side reactions can.<ref name="AtzeniMeyer-ter-Vehn2004">{{cite book |first1=Stefano |last1=Atzeni |first2=Jürgen |last2=Meyer-ter-Vehn |date=3 June 2004 |title=The Physics of Inertial Fusion: BeamPlasma Interaction, Hydrodynamics, Hot Dense Matter |url={{google books |plainurl=y |id=BJcy_p5pUBsC}} |publisher=OUP Oxford |pages=12–13 |isbn=978-0191524059}}</ref>

=== Deuterium, tritium ===
{{main article|Deuterium–tritium fusion}}
[[File:Deuterium-tritium fusion.svg|thumb|upright=0.8|Diagram of the [[D+T|D-T]] reaction]]
The easiest nuclear reaction, at the lowest energy, is D+T:

:{{nuclide|Deuterium|link=yes}} + {{nuclide|Tritium|link=yes}} → {{nuclide|Helium|link=yes}} (3.5 MeV) + {{SubatomicParticle|10neutron|link=yes}} (14.1 MeV)

This reaction is common in research, industrial and military applications, usually as a neutron source. [[Deuterium]] is a naturally occurring [[isotope]] of hydrogen and is commonly available. The large mass ratio of the hydrogen isotopes makes their separation easy compared to the [[uranium enrichment]] process. [[Tritium]] is a natural isotope of hydrogen, but because it has a short [[half-life]] of 12.32 years, it is hard to find, store, produce, and is expensive. Consequently, the deuterium-tritium fuel cycle requires the breeding of tritium from [[lithium]] using one of the following reactions:

:{{SubatomicParticle|10neutron}} + {{nuclide|Lithium|6}} → {{nuclide|Tritium}} + {{nuclide|Helium}}
:{{SubatomicParticle|10neutron}} + {{nuclide|Lithium|7}} → {{nuclide|Tritium}} + {{nuclide|Helium}} + {{SubatomicParticle|10neutron}}

The reactant neutron is supplied by the D-T fusion reaction shown above, and the one that has the greatest energy yield. The reaction with <sup>6</sup>Li is [[exothermic reaction|exothermic]], providing a small energy gain for the reactor. The reaction with <sup>7</sup>Li is [[endothermic reaction|endothermic]], but does not consume the neutron. Neutron multiplication reactions are required to replace the neutrons lost to absorption by other elements. Leading candidate neutron multiplication materials are [[beryllium]] and [[lead]], but the <sup>7</sup>Li reaction helps to keep the neutron population high. Natural lithium is mainly <sup>7</sup>Li, which has a low tritium production [[Neutron cross section|cross section]] compared to <sup>6</sup>Li so most reactor designs use [[breeding blanket]]s with enriched <sup>6</sup>Li.

Drawbacks commonly attributed to D-T fusion power include:

* The supply of neutrons results in [[neutron activation]] of the reactor materials.<ref>{{Cite book|last1=Velarde|first1=Guillermo |title=Nuclear fusion by inertial confinement: a comprehensive treatise|last2=Martínez-Val|first2=José María|last3=Ronen|first3=Yigal|date=1993|publisher=CRC Press|isbn=978-0849369261|location=Boca Raton; Ann Arbor; London|language=en|oclc=468393053}}</ref><sup>:242</sup>
* 80% of the resultant energy is carried off by neutrons, which limits the use of direct energy conversion.<ref>{{cite journal |last1=Iiyoshi |first1=A |last2=Momota |first2=H. |last3=Motojima |first3=O. |display-authors=etal |date=October 1993 |title=Innovative Energy Production in Fusion Reactors |url=http://www.nifs.ac.jp/report/nifs250.html |url-status=dead |journal=National Institute for Fusion Science NIFS |pages=2–3 |bibcode=1993iepf.rept.....I |archive-url=https://web.archive.org/web/20150904055903/http://www.nifs.ac.jp/report/nifs250.html |archive-date=September 4, 2015 |access-date=14 February 2012}}</ref>
* It requires the [[radioisotope]] tritium. Tritium may leak from reactors. Some estimates suggest that this would represent a substantial environmental radioactivity release.<ref>{{Cite web|title=Nuclear Fusion : WNA – World Nuclear Association|url=https://www.world-nuclear.org/information-library/current-and-future-generation/nuclear-fusion-power.aspx|access-date=2020-10-11|website=www.world-nuclear.org}}</ref>

The [[neutron flux]] expected in a commercial D-T fusion reactor is about 100 times that of fission power reactors, posing problems for [[plasma facing material|material design]]. After a series of D-T tests at [[Joint European Torus|JET]], the vacuum vessel was sufficiently radioactive that it required remote handling for the year following the tests.<ref>{{cite journal|last=Rolfe|first=A. C.|title=Remote Handling JET Experience|journal=Nuclear Energy|date=1999|volume=38|issue=5|page=6|url=http://www.iop.org/Jet/fulltext/JETP99028.pdf|access-date=10 April 2012|issn=0140-4067}}</ref>

In a production setting, the neutrons would react with lithium in the breeding blanket composed of lithium ceramic pebbles or liquid lithium, yielding tritium. The energy of the neutrons ends up in the lithium, which would then be transferred to drive electrical production. The lithium blanket protects the outer portions of the reactor from the neutron flux. Newer designs, the advanced tokamak in particular, use lithium inside the reactor core as a design element. The plasma interacts directly with the lithium, preventing a problem known as "recycling". The advantage of this design was demonstrated in the [[Lithium Tokamak Experiment]].

=== Deuterium ===
[[File:Deuterium Deuterium Fusion Cross Section.png|thumbnail|upright=1.7|Deuterium fusion cross section (in square meters) at different ion collision energies]]

Fusing two deuterium nuclei is the second easiest fusion reaction. The reaction has two branches that occur with nearly equal probability:

:{{nuclide|Deuterium}} + {{nuclide|Deuterium}} → {{nuclide|Tritium}} + {{nuclide|Hydrogen}}
:{{nuclide|Deuterium}} + {{nuclide|Deuterium}} → {{nuclide|Helium|3}} + {{SubatomicParticle|10neutron}}

This reaction is also common in research. The optimum energy to initiate this reaction is 15&nbsp;keV, only slightly higher than that for the D-T reaction. The first branch produces tritium, so that a D-D reactor is not tritium-free, even though it does not require an input of tritium or lithium. Unless the tritons are quickly removed, most of the tritium produced is burned in the reactor, which reduces the handling of tritium, with the disadvantage of producing more, and higher-energy, neutrons. The neutron from the second branch of the D-D reaction has an energy of only {{convert|2.45|MeV|abbr=on}}, while the neutron from the D-T reaction has an energy of {{convert|14.1|MeV|abbr=on}}, resulting in greater isotope production and material damage. When the tritons are removed quickly while allowing the <sup>3</sup>He to react, the fuel cycle is called "tritium suppressed fusion".<ref>{{Cite journal |last1=Sawan |first1=M. E. |last2=Zinkle |first2=S. J. |last3=Sheffield |first3=J. |date=2002 |title=Impact of tritium removal and He-3 recycling on structure damage parameters in a D–D fusion system |url=http://dx.doi.org/10.1016/s0920-3796(02)00104-7 |journal=Fusion Engineering and Design |volume=61–62 |pages=561–567 |doi=10.1016/s0920-3796(02)00104-7 |bibcode=2002FusED..61..561S |issn=0920-3796}}</ref> The removed tritium decays to <sup>3</sup>He with a 12.5 year half life. By recycling the <sup>3</sup>He decay into the reactor, the fusion reactor does not require materials resistant to fast neutrons.

Assuming complete tritium burn-up, the reduction in the fraction of fusion energy carried by neutrons would be only about 18%, so that the primary advantage of the D-D fuel cycle is that tritium breeding is not required. Other advantages are independence from lithium resources and a somewhat softer neutron spectrum. The disadvantage of D-D compared to D-T is that the energy confinement time (at a given pressure) must be 30 times longer and the power produced (at a given pressure and volume) is 68 times less.{{Citation needed|date=November 2014}}

Assuming complete removal of tritium and <sup>3</sup>He recycling, only 6% of the fusion energy is carried by neutrons. The tritium-suppressed D-D fusion requires an energy confinement that is 10 times longer compared to D-T and double the plasma temperature.<ref>J. Kesner, D. Garnier, A. Hansen, M. Mauel, and L. Bromberg, ''Nucl Fusion'' 2004; 44, 193</ref>

=== Deuterium, helium-3 ===
A second-generation approach to controlled fusion power involves combining [[helium-3]] (<sup>3</sup>He) and [[deuterium]] (<sup>2</sup>H):

:{{nuclide|Deuterium}} + {{nuclide|Helium|3}} → {{nuclide|Helium}} + {{nuclide|Hydrogen}}

This reaction produces <sup>4</sup>He and a high-energy proton. As with the p-<sup>11</sup>B [[aneutronic fusion]] fuel cycle, most of the reaction energy is released as charged particles, reducing [[neutron activation|activation]] of the reactor housing and potentially allowing more efficient energy harvesting (via any of several pathways).<ref name="Advanced Fuels">{{Cite journal|last=Nevins|first=W. M.|date=1998-03-01|title=A Review of Confinement Requirements for Advanced Fuels|url=https://doi.org/10.1023/A:1022513215080|journal=Journal of Fusion Energy|language=en|volume=17|issue=1|pages=25–32|doi=10.1023/A:1022513215080|bibcode=1998JFuE...17...25N|s2cid=118229833|issn=1572-9591}}</ref> In practice, D-D side reactions produce a significant number of neutrons, leaving p-<sup>11</sup>B as the preferred cycle for aneutronic fusion.<ref name="Advanced Fuels" />

=== Proton, boron-11 ===
Both material science problems and non-proliferation concerns are greatly diminished by [[aneutronic fusion]]. Theoretically, the most reactive aneutronic fuel is <sup>3</sup>He. However, obtaining reasonable quantities of <sup>3</sup>He implies large scale extraterrestrial mining on the Moon or in the atmosphere of Uranus or Saturn. Therefore, the most promising candidate fuel for such fusion is fusing the readily available protium (i.e. a [[proton]]) and [[boron]]. Their fusion releases no neutrons, but produces energetic charged alpha (helium) particles whose energy can directly be converted to electrical power:

:{{nuclide|Hydrogen}} + {{nuclide|Boron|11}} → 3 {{nuclide|Helium}}

Side reactions are likely to yield neutrons that carry only about 0.1% of the power,<ref>{{Cite book |title=Emerging nuclear energy systems 1989: proceedings of the Fifth International Conference on Emerging Nuclear Energy Systems, Karlsruhe, F.R. Germany, July 3–6, 1989|date=1989|publisher=World Scientific |editor=von Möllendorff, Ulrich |editor2=Goel, Balbir |isbn=981-0200102|location=Singapore|oclc=20693180}}</ref><sup>:177–182</sup> which means that [[neutron scattering]] is not used for energy transfer and material activation is reduced several thousand-fold. The optimum temperature for this reaction of 123 keV<ref>{{Cite journal|last1=Feldbacher|first1=Rainer|last2=Heindler|first2=Manfred|date=1988|title=Basic cross section data for aneutronic reactor |journal=Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment|volume=271|issue=1|pages=55–64|doi=10.1016/0168-9002(88)91125-4|bibcode=1988NIMPA.271...55F|issn=0168-9002}}</ref> is nearly ten times higher than that for pure hydrogen reactions, and energy confinement must be 500 times better than that required for the D-T reaction. In addition, the [[power density]] is 2500 times lower than for D-T, although per unit mass of fuel, this is still considerably higher compared to fission reactors.

Because the confinement properties of the tokamak and laser pellet fusion are marginal, most proposals for aneutronic fusion are based on radically different confinement concepts, such as the [[Polywell]] and the [[Dense Plasma Focus]]. In 2013, a research team led by [[Christine Labaune]] at [[École Polytechnique]], reported a new fusion rate record for proton-boron fusion, with an estimated 80&nbsp;million fusion reactions during a 1.5 nanosecond laser fire, 100 times greater than reported in previous experiments.<ref>{{cite web|url=http://www.livescience.com/40246-new-boron-method-nuclear-fusion.html|title=Nuclear Fusion: Laser-Beam Experiment Yields Exciting Results|website=LiveScience.com|date=October 8, 2013}}</ref><ref>{{cite web|url=http://www.fusenet.eu/node/575|title=Record proton-boron fusion rate achieved – FuseNet|website=www.fusenet.eu|access-date=2014-11-26|archive-url=https://web.archive.org/web/20141202062802/http://www.fusenet.eu/node/575|archive-date=2014-12-02|url-status=dead}}</ref>

== Material selection ==
{{Further|International Fusion Materials Irradiation Facility}}

Structural material stability is a critical issue.<ref name="Materials">{{Cite book|last=Roberts, J. T. Adrian |title=Structural Materials in Nuclear Power Systems|date=1981|publisher=Springer US|isbn=978-1468471960|location=Boston, MA|oclc=853261260}}</ref><ref>{{Cite web|date=2021-09-09|title=Roadmap highlights materials route to fusion|url=https://www.theengineer.co.uk/fusion-materials/|access-date=2021-09-17|website=The Engineer|language=en-US}}</ref> Materials that can survive the high temperatures and neutron bombardment experienced in a fusion reactor are considered key to success.<ref>{{Cite journal |last=Klueh |first=R. L. |title=Metals in the nuclear-fusion environment |journal=Materials Engineering |volume=99 |pages=39–42}}</ref><ref name="Materials" /> The principal issues are the conditions generated by the plasma, neutron degradation of wall surfaces, and the related issue of plasma-wall surface conditions.<ref>{{Cite thesis|title=Interaction of atomic hydrogen with materials used for plasma-facing wall in fusion devices |type=Doctorate |publisher=[A. Založnik]|date=2016|place=Ljubljana|language=en|first=Anže|last=Založnik|oclc = 958140759}}</ref><ref>{{Cite journal |last=McCracken |first=G. M. |date=1997 |title=Plasma surface interactions in controlled fusion devices |url=http://dx.doi.org/10.1088/0029-5515/37/3/413 |journal=Nuclear Fusion |volume=37 |issue=3 |pages=427–429 |doi=10.1088/0029-5515/37/3/413 |issn=0029-5515 |s2cid=250776874}}</ref> Reducing hydrogen permeability is seen as crucial to hydrogen recycling<ref>{{Citation|last=Mioduszewski|first=Peter|title=Hydrogen Recycling and Wall Equilibration in Fusion Devices |date=2000|url=http://dx.doi.org/10.1007/978-94-011-4331-8_23|work=Hydrogen Recycling at Plasma Facing Materials|pages=195–201|place=Dordrecht|publisher=Springer Netherlands|doi=10.1007/978-94-011-4331-8_23|isbn=978-0792366300|access-date=2020-10-13}}</ref> and control of the tritium inventory.<ref name="permeation">{{Cite journal|last=Nemanič|first=Vincenc|date=2019|title=Hydrogen permeation barriers: Basic requirements, materials selection, deposition methods, and quality evaluation|journal=Nuclear Materials and Energy|volume=19|pages=451–457|doi=10.1016/j.nme.2019.04.001|issn=2352-1791|doi-access=free|bibcode=2019NMEne..19..451N }}</ref> Materials with the lowest bulk hydrogen solubility and diffusivity provide the optimal candidates for stable barriers. A few pure metals, including tungsten and beryllium,<ref>{{cite web|url=https://www.americanelements.com/fusion-energy|title=American Elements Creates Detection Window for EPFL Fusion Reactor|access-date=16 February 2023|publisher=American Elements}}</ref> and compounds such as carbides, dense oxides, and nitrides have been investigated. Research has highlighted that coating techniques for preparing well-adhered and perfect barriers are of equivalent importance. The most attractive techniques are those in which an ad-layer is formed by oxidation alone. Alternative methods utilize specific gas environments with strong magnetic and electric fields. Assessment of barrier performance represents an additional challenge. Classical coated membranes gas permeation continues to be the most reliable method to determine hydrogen permeation barrier (HPB) efficiency.<ref name="permeation" /> In 2021, in response to increasing numbers of designs for fusion power reactors for 2040, the [[United Kingdom Atomic Energy Authority]] published the [https://www.royce.ac.uk/content/uploads/2021/09/UK_Fusion_Materials_Roadmap_Interactive.pdf UK Fusion Materials Roadmap 2021–2040], focusing on five priority areas, with a focus on tokamak family reactors:

* Novel materials to minimize the amount of activation in the structure of the fusion power plant;
* Compounds that can be used within the power plant to optimise breeding of tritium fuel to sustain the fusion process;
* Magnets and insulators that are resistant to irradiation from fusion reactions—especially under cryogenic conditions;
* Structural materials able to retain their strength under neutron bombardment at high operating temperatures (over 550 degrees C);
* Engineering assurance for fusion materials—providing irradiated sample data and modelled predictions such that plant designers, operators and regulators have confidence that materials are suitable for use in future commercial power stations.

=== Superconducting materials ===
[[File:SuperOX Wire Production from 2013 to 2021.png|thumbnail|upright=1.5|SuperOx was able to produce over 186 miles of YBCO wire in nine months for use in fusion reactor magnets, dramatically surpassing the company's previous production targets.]]

In a plasma that is embedded in a magnetic field (known as a magnetized plasma) the fusion rate scales as the magnetic field strength to the 4th power. For this reason, many fusion companies that rely on magnetic fields to control their plasma are trying to develop high temperature superconducting devices. In 2021, SuperOx, a Russian and Japanese company, developed a new manufacturing process for making superconducting [[YBCO]] wire for fusion reactors. This new wire was shown to conduct between 700 and 2000 Amps per square millimeter. The company was able to produce 186 miles of wire in nine months.<ref>Molodyk, A., et al. "Development and large volume production of extremely high current density YBa2Cu3O7 superconducting wires for fusion." ''Scientific Reports'' 11.1 (2021): 1–11.</ref>

=== Containment considerations ===
Even on smaller production scales, the containment apparatus is blasted with matter and energy. Designs for plasma containment must consider:

* A heating and cooling cycle, up to a 10&nbsp;MW/m<sup>2</sup> thermal load.
* [[Neutron radiation]], which over time leads to [[neutron activation]] and [[embrittlement]].
* High energy ions leaving at tens to hundreds of [[electronvolt]]s.
* [[Alpha particle]]s leaving at millions of [[electronvolt]]s.
* Electrons leaving at high energy.
* Light radiation (IR, visible, UV, X-ray).

Depending on the approach, these effects may be higher or lower than fission reactors.<ref name="Shin Kajita 2014">"Thermal response of nanostructured tungsten". Shin Kajita, et al., January 2014, Nuclear Fusion 54 (2014) 033005 (10 pp.)</ref> One estimate put the [[neutron radiation|radiation]] at 100 times that of a typical [[pressurized water reactor]].{{Citation needed|date=March 2014}} Depending on the approach, other considerations such as [[electrical conductivity]], [[Vacuum permeability|magnetic permeability]], and mechanical strength matter. Materials must also not end up as long-lived [[radioactive waste]].<ref name="Materials" />

=== Plasma-wall surface conditions ===
For long term use, each atom in the wall is expected to be hit by a neutron and displaced about 100 times before the material is replaced. These high-energy neutron collisions with the atoms in the wall result in the absorption of the neutrons, forming unstable isotopes of the atoms. When the isotope decays, it may emit [[alpha particles]], [[protons]], or [[gamma rays]]. Alpha particles, once stabilized by capturing electrons, form helium atoms which accumulate at grain boundaries and may result in swelling, blistering, or embrittlement of the material.<ref name="Shin Kajita 2014"/><ref>{{cite journal |last1=Gilbert |first1=Mark |title=Neutron-induced dpa, transmutations, gas production, and helium embrittlement of fusion materials |journal=Journal of Nuclear Materials |date=2013 |volume=442 |issue=1–3 |pages=S755–S760 |doi=10.1016/j.jnucmat.2013.03.085|arxiv=1311.5079 |bibcode=2013JNuM..442S.755G }}</ref>

=== Selection of materials ===
[[Tungsten]] is widely regarded as the optimal material for plasma-facing components in next-generation fusion devices due to its unique properties and potential for enhancements. Its low sputtering rates and high melting point make it particularly suitable for the high-stress environments of fusion reactors, allowing it to withstand intense conditions without rapid degradation. Additionally, tungsten's low [[tritium]] retention through co-deposition and implantation is essential in fusion contexts, as it helps to minimize the accumulation of this radioactive isotope.<ref>{{cite journal |last1=Neu |first1=R. |last2=Dux |first2=R. |display-authors=1|title=Tungsten: an option for divertor and main chamber plasma facing components in future fusion devices |journal=Nuclear Fusion |date=2005 |volume=45 |issue=3 |pages=209–218|doi=10.1088/0029-5515/45/3/007|bibcode=2005NucFu..45..209N |s2cid=56572005 }}</ref><ref>{{cite journal |last1=Philipps |first1=V. |last2=Noname |first2=N. |display-authors=1|title=Tungsten as material for plasma-facing components in fusion devices |journal=Journal of Nuclear Materials |date=2011 |volume=415|issue=1 |pages=S2–S9|doi=10.1016/j.jnucmat.2011.01.110|bibcode=2011JNuM..415S...2P }}</ref><ref>{{cite journal |last1=Neu |first1=R. |last2=Riesch |first2=J. |display-authors=1|title=Advanced tungsten materials for plasma-facing components of DEMO and fusion power plants |journal=Fusion Engineering and Design |date=2016 |volume=109-111 |pages=1046–1052|doi=10.1016/j.fusengdes.2016.01.027|bibcode=2016FusED.109.1046N |hdl=11858/00-001M-0000-002B-3142-7 |hdl-access=free }}</ref><ref>{{cite journal |last1=Coenen |first1=J.W.|title=Fusion Materials Development at Forschungszentrum Jülich |journal=Advanced Engineering Materials|date=2020 |volume=22 |issue=6 |pages=1901376|doi=10.1002/adem.201901376|doi-access=free }}</ref>

Liquid metals (lithium, [[gallium]], [[tin]]) have been proposed, e.g., by injection of 1–5&nbsp;mm thick streams flowing at 10&nbsp;m/s on solid substrates.{{Citation needed|date=March 2014}}

Graphite features a gross erosion rate due to physical and chemical [[sputtering]] amounting to many meters per year, requiring redeposition of the sputtered material. The redeposition site generally does not exactly match the sputter site, allowing net erosion that may be prohibitive. An even larger problem is that tritium is redeposited with the redeposited graphite. The tritium inventory in the wall and dust could build up to many kilograms, representing a waste of resources and a radiological hazard in case of an accident. Graphite found favor as material for short-lived experiments, but appears unlikely to become the primary [[plasma-facing material]] (PFM) in a commercial reactor.<ref name="Materials" /><ref>{{Cite journal|title= Plasma–surface interaction in the stellarator W7-X: Conclusions drawn from operation with graphite plasma-facing components|journal=Nuclear Fusion|date=December 2, 2021 |volume=62 |issue=1 |page=016006 |doi=10.1088/1741-4326/ac3508 |s2cid=240484560 |last1=Brezɩnsek |first1=S. |last2=Dhard |first2=C. P. |last3=Jakubowski |first3=M. |last4=König |first4=R. |last5=Masuzaki |first5=S. |last6=Mayer |first6=M. |last7=Naujoks |first7=D. |last8=Romazanov |first8=J. |last9=Schmid |first9=K. |last10=Schmitz |first10=O. |last11=Zhao |first11=D. |last12=Balden |first12=M. |last13=Brakel |first13=R. |last14=Butterschoen |first14=B. |last15=Dittmar |first15=T. |last16=Drews |first16=P. |last17=Effenberg |first17=F. |last18=Elgeti |first18=S. |last19=Ford |first19=O. |last20=Fortuna-Zalesna |first20=E. |last21=Fuchert |first21=G. |last22=Gao |first22=Y. |last23=Goriaev |first23=A. |last24=Hakola |first24=A. |last25=Kremeyer |first25=T. |last26=Krychowiak |first26=M. |last27=Liang |first27=Y. |last28=Linsmeier |first28=Ch |last29=Lunsford |first29=R. |last30=Motojima |first30=G. |display-authors=1 |doi-access=free }}</ref>

Ceramic materials such as silicon carbide (SiC) have similar issues like graphite. Tritium retention in silicon carbide plasma-facing components is approximately 1.5-2 times higher than in graphite, resulting in reduced fuel efficiency and heightened safety risks in fusion reactors. SiC tends to trap more tritium, limiting its availability for fusion and increasing the risk of hazardous accumulation, complicating tritium management.<ref>{{cite journal |last1=Mayer |first1=M. |last2=Balden |first2=M. |last3=Behrisch |first3=R. |title=Deuterium retention in carbides and doped graphites |journal=Journal of Nuclear Materials |date=1998 |volume=252 |issue=1 |pages=55–62 |doi=10.1016/S0022-3115(97)00299-7 |bibcode=1998JNuM..252...55M |url=https://www.sciencedirect.com/science/article/pii/S0022311597002997 }}</ref><ref>{{cite journal |last1=Koller |first1=Markus T. |last2=Davis |first2=James W. |last3=Goodland |first3=Megan E. |last4=Abrams |first4=Tyler |last5=Gonderman |first5=Sean |last6=Herdrich |first6=Georg |last7=Frieß |first7=Martin |last8=Zuber |first8=Christian |title=Deuterium retention in silicon carbide, SiC ceramic matrix composites, and SiC coated graphite |journal=Nuclear Materials and Energy |date=2019 |volume=20 |pages=100704 |doi=10.1016/j.nme.2019.100704 |bibcode=2019NMEne..2000704K |doi-access=free }}</ref> Furthermore, the chemical and physical sputtering of SiC remains significant, contributing to tritium buildup through co-deposition over time and with increasing particle fluence. As a result, carbon-based materials have been excluded from [[ITER]], [[DEMOnstration Power Plant|DEMO]], and similar devices.<ref>{{cite journal |last1=Roth |first1=Joachim |last2=Tsitrone |first2=E. |last3=Loarte |first3=A. |last4=Loarer |first4=Th. |last5=Counsell |first5=G. |last6=Neu |first6=R. |last7=Philipps |first7=V. |last8=Brezinsek |first8=S. |last9=Lehnen |first9=M. |last10=Coad |first10=P. |last11=Grisolia |first11=Ch. |last12=Schmid |first12=K. |last13=Krieger |first13=K. |last14=Kallenbach |first14=A. |last15=Lipschultz |first15=B. |last16=Doerner |first16=R. |last17=Causey |first17=R. |last18=Alimov |first18=V. |last19=Shu |first19=W. |last20=Ogorodnikova |first20=O. |last21=Kirschner |first21=A. |last22=Federici |first22=G. |last23=Kukushkin |first23=A. |title=Recent analysis of key plasma wall interactions issues for ITER |journal=Journal of Nuclear Materials |date=2009 |volume=390-391 |pages=1–9 |doi=10.1016/j.jnucmat.2009.01.037 |bibcode=2009JNuM..390....1R |hdl=11858/00-001M-0000-0026-F442-2 |url=https://www.sciencedirect.com/science/article/pii/S0022311509000506 |issn=0022-3115|hdl-access=free }}</ref> 

Tungsten's sputtering rate is orders of magnitude smaller than carbon's, and tritium is much less incorporated into redeposited tungsten. However, tungsten plasma impurities are much more damaging than carbon impurities, and self-sputtering can be high, requiring the plasma in contact with the tungsten not be too hot (a few tens of eV rather than hundreds of eV). Tungsten also has issues around eddy currents and melting in off-normal events, as well as some radiological issues.<ref name="Materials" />

Recent advances in materials for containment apparatus materials have found that certain ceramics can actually improve the longevity of the material of the containment apparatus. Studies on [[MAX phases]], such as titanium silicon carbide, show that under the high operating temperatures of nuclear fusion, the material undergoes a phase transformation from a hexagonal structure to a face-centered-cubic (FCC) structure, driven by helium bubble growth. Helium atoms preferentially accumulate in the Si layer of the hexagonal structure, as the Si atoms are more mobile than the Ti-C slabs. As more atoms are trapped, the Ti-C slab is peeled off, causing the Si atoms to become highly mobile interstitial atoms in the new FCC structure. Lattice strain induced by the He bubbles cause Si atoms to diffuse out of compressive areas, typically towards the surface of the material, forming a protective silicon dioxide layer.<ref>{{cite journal |last1=Su |first1=Ranran |title=Helium-driven element depletion and phase transformation in irradiated Ti3SiC2 at high temperature |journal=Journal of the European Ceramic Society |date=2023 |volume=43 |issue=8 |pages=3104–3111 |doi=10.1016/j.jeurceramsoc.2023.01.048}}</ref>

Doping vessel materials with iron silicate has emerged as a promising approach to enhance containment materials in fusion reactors, as well. This method targets helium embrittlement at grain boundaries, a common issue that arises as helium atoms accumulate and form bubbles. Over time, these bubbles coalesce at grain boundaries, causing them to expand and degrade the material's structural integrity. By contrast, introducing iron silicate creates [[nucleation]] sites within the metal matrix that are more thermodynamically favorable for helium aggregation. This localized congregation around iron silicate nanoparticles induces matrix strain rather than weakening grain boundaries, preserving the material’s strength and longevity.<ref>{{cite journal |last1=Myat-Hyun |first1=Myat |title=Tailoring mechanical and in vitro biological properties of calcium‒silicate based bioceramic through iron doping in developing future material |journal=Journal of the Mechanical Behavior of Biomedical Materials |date=2022 |volume=128 |doi=10.1016/j.jmbbm.2022.105122|pmid=35168129 }}</ref><ref>{{cite web |last1=Stauffer |first1=Nancy |title=More durable metals for fusion power reactors |url=https://news.mit.edu/2024/more-durable-metals-fusion-power-reactors-0819 |website=MIT News|date=August 19, 2024 }}</ref>

== Safety and the environment ==
=== Accident potential ===
Accident potential and effect on the environment are critical to social acceptance of nuclear fusion, also known as a [[Corporate social responsibility|social license]].<ref>{{Cite journal |last=Hoedl |first=Seth A. |date=2022 |title=Achieving a social license for fusion energy |url=http://dx.doi.org/10.1063/5.0091054 |journal=Physics of Plasmas |volume=29 |issue=9 |pages=092506 |doi=10.1063/5.0091054 |bibcode=2022PhPl...29i2506H |s2cid=252454077 |issn=1070-664X}}</ref> Fusion reactors are not subject to [[Nuclear meltdown|catastrophic meltdown]].<ref name="McCrackenStott2012"/> It requires precise and controlled temperature, pressure and magnetic field parameters to produce net energy, and any damage or loss of required control would rapidly quench the reaction.<ref name=afraid>{{cite web |url=http://www.iter.org/newsline/107/1489 |title=Who is afraid of ITER? |first=Krista |last=Dulon |website=iter.org |date=2012 |access-date=18 August 2012 |archive-url=https://web.archive.org/web/20121130221734/http://www.iter.org/newsline/107/1489 |archive-date=November 30, 2012 |url-status=dead }}</ref> Fusion reactors operate with seconds or even microseconds worth of fuel at any moment. Without active refueling, the reactions immediately quench.<ref name="McCrackenStott2012">{{cite book|last1=McCracken|first1=Garry |last2=Stott|first2=Peter |title=Fusion: The Energy of the Universe|url={{google books|plainurl=y|id=e6jEZfO2gO4C|page=198}}|access-date=18 August 2012|date=2012|publisher=Academic Press|isbn=978-0123846563|pages=198–199}}</ref>

The same constraints prevent runaway reactions. Although the plasma is expected to have a volume of {{Convert|1000|m3|ft3|abbr=on}} or more, the plasma typically contains only a few grams of fuel.<ref name="McCrackenStott2012" /> By comparison, a fission reactor is typically loaded with enough fuel for months or years, and no additional fuel is necessary to continue the reaction. This large fuel supply is what offers the possibility of a meltdown.<ref name="n">{{cite book|last=Angelo|first=Joseph A. |title=Nuclear Technology|url={{google books|plainurl=y|id=ITfaP-xY3LsC|page=474}}|access-date=18 August 2012|date=2004|publisher=Greenwood Publishing Group|isbn=978-1573563369|page=474}}</ref>

In magnetic containment, strong fields develop in coils that are mechanically held in place by the reactor structure. Failure of this structure could release this tension and allow the magnet to "explode" outward. The severity of this event would be similar to other industrial accidents or an [[MRI]] machine quench/explosion, and could be effectively contained within a [[containment building]] similar to those used in fission reactors.

In laser-driven inertial containment the larger size of the reaction chamber reduces the stress on materials. Although failure of the reaction chamber is possible, stopping fuel delivery prevents catastrophic failure.<ref name="economic prospects">{{Cite book |title=Safety, environmental impact, and economic prospects of nuclear fusion|date=1990|publisher=Plenum Press|editor=Brunelli, B. |editor2=Knoepfel, Heinz |isbn=978-1461306191|location=New York|oclc=555791436}}</ref>

Most reactor designs rely on [[liquid hydrogen]] as a coolant and to convert stray neutrons into [[tritium]], which is fed back into the reactor as fuel. Hydrogen is flammable, and it is possible that hydrogen stored on-site could ignite. In this case, the tritium fraction of the hydrogen would enter the atmosphere, posing a radiation risk. Calculations suggest that about {{convert|1|kg}} of tritium and other radioactive gases in a typical power station would be present. The amount is small enough that it would dilute to legally acceptable limits by the time they reached the station's [[perimeter fence]].<ref name="WorldEnergyCouncil" />

The likelihood of small industrial accidents, including the local release of radioactivity and injury to staff, are estimated to be minor compared to fission. They would include accidental releases of lithium or tritium or mishandling of radioactive reactor components.<ref name="economic prospects" />

=== Magnet quench ===
A [[magnet quench]] is an abnormal termination of magnet operation that occurs when part of the superconducting coil exits the superconducting state (becomes normal). This can occur because the field inside the magnet is too large, the rate of change of field is too large (causing [[eddy current]]s and resultant [[Joule heating|heating]] in the copper support matrix), or a combination of the two.

More rarely a magnet defect can cause a quench. When this happens, that particular spot is subject to rapid [[Joule heating]] from the current, which raises the [[temperature]] of the surrounding regions. This pushes those regions into the normal state as well, which leads to more heating in a chain reaction. The entire magnet rapidly becomes normal over several seconds, depending on the size of the superconducting coil. This is accompanied by a loud bang as the energy in the magnetic field is converted to heat, and the [[cryogenics|cryogenic]] fluid boils away. The abrupt decrease of current can result in [[kilovolt]] inductive voltage spikes and arcing. Permanent damage to the magnet is rare, but components can be damaged by localized heating, high voltages, or large mechanical forces.

In practice, magnets usually have safety devices to stop or limit the current when a quench is detected. If a large magnet undergoes a quench, the inert vapor formed by the evaporating cryogenic fluid can present a significant [[asphyxiation]] hazard to operators by displacing breathable air.

A large section of the superconducting magnets in [[CERN]]'s [[Large Hadron Collider]] unexpectedly quenched during start-up operations in 2008, destroying multiple magnets.<ref>{{Cite book|url=https://edms.cern.ch/ui/file/973073/1/Report_on_080919_incident_at_LHC__2_.pdf|title=Interim Summary Report on the Analysis of the 19 September 2008 Incident at the LHC|publisher=CERN|year=2008}}</ref> In order to prevent a recurrence, the LHC's superconducting magnets are equipped with fast-ramping heaters that are activated when a quench event is detected. The dipole bending magnets are connected in series. Each power circuit includes 154 individual magnets, and should a quench event occur, the entire combined stored energy of these magnets must be dumped at once. This energy is transferred into massive blocks of metal that heat up to several hundred degrees Celsius—because of resistive heating—in seconds. A magnet quench is a "fairly routine event" during the operation of a particle accelerator.<ref>{{cite web|last=Peterson|first=Tom|title=Explain it in 60 seconds: Magnet Quench|url=http://www.symmetrymagazine.org/article/november-2008/explain-it-in-60-seconds-magnet-quench|website=Symmetry Magazine|date=November 2008 |publisher=[[Fermilab]]/[[SLAC]]|access-date=15 February 2013}}</ref>

=== Effluents ===
The natural product of the fusion reaction is a small amount of [[helium]], which is harmless to life. Hazardous tritium is difficult to retain completely.

Although tritium is volatile and biologically active, the health risk posed by a release is much lower than that of most radioactive contaminants, because of tritium's short half-life (12.32 years) and very low decay energy (~14.95&nbsp;keV), and because it does not [[bioaccumulation|bioaccumulate]] (it cycles out of the body as water, with a [[biological half-life]] of 7 to 14 days).<ref name="nuclearsafety-petrangeli">{{cite book|first=Gianni |last=Petrangeli|title=Nuclear Safety|url={{google books |plainurl=y |id=5X2Hxad9BoQC|page=430}} |date=2006|publisher=Butterworth-Heinemann|isbn=978-0750667234|page=430}}</ref> ITER incorporates total containment facilities for tritium.<ref name="ITER" />

=== Radioactive waste ===
{{See also|Radioactive waste}}

Fusion reactors create far less radioactive material than fission reactors. Further, the material it creates is less damaging biologically, and the radioactivity dissipates within a time period that is well within existing engineering capabilities for safe long-term waste storage.<ref name="demonstration">{{Cite journal |last1=Gonzalez de Vicente |first1=Sehila M. |last2=Smith |first2=Nicholas A. |last3=El-Guebaly |first3=Laila |last4=Ciattaglia |first4=Sergio |last5=Di Pace |first5=Luigi |last6=Gilbert |first6=Mark |last7=Mandoki |first7=Robert |last8=Rosanvallon |first8=Sandrine |last9=Someya |first9=Youji |last10=Tobita |first10=Kenji |last11=Torcy |first11=David |date=2022-08-01 |title=Overview on the management of radioactive waste from fusion facilities: ITER, demonstration machines and power plants |journal=Nuclear Fusion |volume=62 |issue=8 |pages=085001 |doi=10.1088/1741-4326/ac62f7 |bibcode=2022NucFu..62h5001G |s2cid=247920590 |issn=0029-5515|doi-access=free }}</ref> In specific terms, except in the case of [[aneutronic fusion]],<ref>{{Cite book|last1=Harms|first1=A. A.|url=https://books.google.com/books?id=DD0sZgutqowC&pg=PA8|title=Principles of Fusion Energy: An Introduction to Fusion Energy for Students of Science and Engineering|last2=Schoepf|first2=Klaus F.|last3=Kingdon|first3=David Ross|date=2000|publisher=World Scientific|isbn=978-9812380333|language=en}}</ref><ref>{{Cite journal|last1=Carayannis|first1=Elias G.|last2=Draper|first2=John|last3=Iftimie|first3=Ion A.|date=2020|title=Nuclear Fusion Diffusion: Theory, Policy, Practice, and Politics Perspectives |url=https://ieeexplore.ieee.org/document/9078039|journal=IEEE Transactions on Engineering Management|volume=69 |issue=4 |pages=1237–1251|doi=10.1109/TEM.2020.2982101|s2cid=219001461|issn=1558-0040}}</ref> the neutron flux turns the structural materials radioactive. The amount of radioactive material at shut-down may be comparable to that of a fission reactor, with important differences. The half-lives of fusion and neutron activation [[radioisotopes]] tend to be less than those from fission, so that the hazard decreases more rapidly. Whereas fission reactors produce waste that remains radioactive for thousands of years, the radioactive material in a fusion reactor (other than tritium) would be the reactor core itself and most of this would be radioactive for about 50 years, with other low-level waste being radioactive for another 100 years or so thereafter.<ref>{{cite journal |first1=Anil |last1=Markandya |first2=Paul |last2=Wilkinson |s2cid=25504602 |url=http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(07)61253-7/fulltext |journal=The Lancet |volume=370 |issue=9591 |year=2007 |title=Electricity generation and health |pages=979–990 |doi=10.1016/S0140-6736(07)61253-7 |pmid=17876910 |access-date=February 21, 2018}}</ref> The fusion waste's short half-life eliminates the challenge of long-term storage. By 500 years, the material would have the same [[radiotoxicity]] as [[coal ash]].<ref name="WorldEnergyCouncil">{{cite web |last1=Hamacher |first1=T. |last2=Bradshaw |first2=A. M. |date=October 2001 |title=Fusion as a Future Power Source: Recent Achievements and Prospects |url=http://www.worldenergy.org/wec-geis/publications/default/tech_papers/18th_Congress/downloads/ds/ds6/ds6_5.pdf |archive-url=https://web.archive.org/web/20040506065141/http://www.worldenergy.org/wec-geis/publications/default/tech_papers/18th_Congress/downloads/ds/ds6/ds6_5.pdf |archive-date=2004-05-06 |publisher=World Energy Council}}</ref>
Nonetheless, classification as intermediate level waste rather than low-level waste may complicate safety discussions.<ref>{{Cite journal|last1=Nicholas|first1=T. E. G.|last2=Davis|first2=T. P.|last3=Federici|first3=F.|last4=Leland|first4=J.|last5=Patel|first5=B. S.|last6=Vincent|first6=C.|last7=Ward|first7=S. H.|date=2021-02-01|title=Re-examining the role of nuclear fusion in a renewables-based energy mix|url=https://www.sciencedirect.com/science/article/pii/S0301421520307540|journal=Energy Policy|language=en|volume=149|pages=112043|doi=10.1016/j.enpol.2020.112043|issn=0301-4215|arxiv=2101.05727|bibcode=2021EnPol.14912043N |s2cid=230570595}}</ref><ref name="demonstration" />

The choice of materials is less constrained than in conventional fission, where many materials are required for their specific [[neutron cross-section]]s. Fusion reactors can be designed using "low activation", materials that do not easily become radioactive. [[Vanadium]], for example, becomes much less radioactive than [[stainless steel]].<ref>{{Cite journal |last1=Cheng |first1=E. T. |last2=Muroga |first2=Takeo |date=2001 |title=Reuse of Vanadium Alloys in Power Reactors |url=http://dx.doi.org/10.13182/fst01-a11963369 |journal=Fusion Technology |volume=39 |issue=2P2 |pages=981–985 |bibcode=2001FuTec..39..981C |doi=10.13182/fst01-a11963369 |issn=0748-1896 |s2cid=124455585}}</ref> [[Carbon fiber]] materials are also low-activation, are strong and light, and are promising for laser-inertial reactors where a magnetic field is not required.<ref>{{Cite journal|last1=Streckert|first1=H. H.|last2=Schultz|first2=K. R.|last3=Sager|first3=G. T.|last4=Kantncr|first4=R. D.|date=1996-12-01|title=Conceptual Design of Low Activation Target Chamber and Components for the National Ignition Facility|url=https://doi.org/10.13182/FST96-A11962981|journal=Fusion Technology|volume=30|issue=3P2A|pages=448–451|doi=10.13182/FST96-A11962981|bibcode=1996FuTec..30..448S |issn=0748-1896|citeseerx=10.1.1.582.8236}}</ref>

=== Nuclear proliferation ===
{{Main|Nuclear proliferation}}

In some scenarios, fusion power technology could be adapted to produce materials for military purposes. A huge amount of [[tritium]] could be produced by a fusion power station; tritium is used in the trigger of hydrogen bombs and in modern [[boosted fission weapon]]s, but it can be produced in other ways. The energetic neutrons from a fusion reactor could be used to breed weapons-grade [[plutonium]] or [[uranium]] for an atomic bomb (for example by transmutation of {{chem|238|U}} to {{chem|239|Pu}}, or {{chem|232|Th}} to {{chem|233|U}}).

A study conducted in 2011 assessed three scenarios:<ref name="ProliferationRisk_Goldston" />
* Small-scale fusion station: As a result of much higher power consumption, heat dissipation and a more recognizable design compared to enrichment [[gas centrifuge]]s, this choice would be much easier to detect and therefore implausible.<ref name="ProliferationRisk_Goldston" />
* Commercial facility: The production potential is significant. But no fertile or fissile substances necessary for the production of weapon-usable materials needs to be present at a civil fusion system at all. If not shielded, detection of these materials can be done by their characteristic [[Gamma Radiation|gamma radiation]]. The underlying redesign could be detected by regular design information verification. In the (technically more feasible) case of solid breeder blanket modules, it would be necessary for incoming components to be inspected for the presence of fertile material,<ref name="ProliferationRisk_Goldston" /> otherwise plutonium for several weapons could be produced each year.<ref name="StrongNeutronSources" />
* Prioritizing weapon-grade material regardless of secrecy: The fastest way to produce weapon-usable material was seen in modifying a civil fusion power station. No weapons-compatible material is required during civil use. Even without the need for covert action, such a modification would take about two months to start production and at least an additional week to generate a significant amount. This was considered to be enough time to detect a military use and to react with diplomatic or military means. To stop the production, a military destruction of parts of the facility while leaving out the reactor would be sufficient.<ref name="ProliferationRisk_Goldston" />

Another study concluded "...large fusion reactors—even if not designed for fissile material breeding—could easily produce several hundred kg Pu per year with high weapon quality and very low source material requirements." It was emphasized that the implementation of features for intrinsic proliferation resistance might only be possible at an early phase of research and development.<ref name="StrongNeutronSources" /> The theoretical and computational tools needed for hydrogen bomb design are closely related to those needed for [[inertial confinement fusion]], but have very little in common with magnetic confinement fusion.

=== Fuel reserves ===
Fusion power commonly proposes the use of deuterium as fuel and many current designs also use [[lithium]]. Assuming a fusion energy output equal to the 1995 global power output of about 100 [[exa-|E]]J/yr (= 1 × 10<sup>20</sup> J/yr) and that this does not increase in the future, which is unlikely, then known current lithium reserves would last 3000 years. Lithium from sea water would last 60&nbsp;million years, however, and a more complicated fusion process using only deuterium would have fuel for 150&nbsp;billion years.<ref>{{cite web|url=http://www.agci.org/dB/PDFs/03S2_MMauel_SafeFusion%3F.pdf |archive-url=https://web.archive.org/web/20110727135814/http://www.agci.org/dB/PDFs/03S2_MMauel_SafeFusion?.pdf |url-status=dead |archive-date=2011-07-27 |title=Energy for Future Centuries |access-date=2013-06-22 }}</ref> To put this in context, 150&nbsp;billion years is close to 30 times the remaining lifespan of the Sun,<ref name="sunlife">{{cite web |last=Christian |first=Eric |display-authors=etal |title=Cosmicopia |url=http://helios.gsfc.nasa.gov/qa_sun.html#sunlife |url-status=dead |archive-url=https://web.archive.org/web/20111106095009/http://helios.gsfc.nasa.gov/qa_sun.html#sunlife |archive-date=November 6, 2011 |access-date=2009-03-20 |publisher=NASA}}</ref> and more than 10 times the estimated age of the universe.

== Economics ==
The EU spent almost {{nowrap|€10 billion}} through the 1990s.<ref>{{cite web|author=Fusion For Energy|title=Fusion For Energy – Bringing the power of the sun to earth|url=http://www.f4e.europa.eu|url-status=dead|archive-url=https://web.archive.org/web/20191129201922/https://f4e.europa.eu/|archive-date=November 29, 2019|access-date=July 17, 2020|website=f4e.europa.eu}}</ref> [[ITER]] represents an investment of over twenty billion dollars, and possibly tens of billions more, including [[In kind|in kind contributions]].<ref>{{Cite journal|date=2016|title=ITER governing council pushes schedule back five years and trims budget|journal=Physics Today|issue=6 |page=8171 |doi=10.1063/pt.5.029905|bibcode=2016PhT..2016f8171. |issn=1945-0699}}</ref><ref>{{Cite journal|year=2018|title=ITER disputes DOE's cost estimate of fusion project|journal=Physics Today|doi=10.1063/PT.6.2.20180416a |last1=Kramer |first1=David |issue=4 |page=4990 |bibcode=2018PhT..2018d4990K }}</ref> Under the European Union's [[Framework Programmes for Research and Technological Development|Sixth Framework Programme]], nuclear fusion research received {{nowrap|€750 million}} (in addition to ITER funding), compared with {{nowrap|€810 million}} for sustainable energy research,<ref>{{cite web |title=The Sixth Framework Programme in brief |publisher=ec.europa.eu |url= http://ec.europa.eu/research/fp6/pdf/fp6-in-brief_en.pdf |access-date=30 October 2014}}</ref> putting research into fusion power well ahead of that of any single rival technology. The [[United States Department of Energy]] has allocated $US367M–$US671M every year since 2010, peaking in 2020,<ref>{{cite web |last1=Margraf |first1=Rachel |title=A Brief History of U.S. Funding of Fusion Energy |url=http://large.stanford.edu/courses/2021/ph241/margraf1/ |access-date=21 July 2021}}</ref> with plans to reduce investment to $US425M in its FY2021 Budget Request.<ref>DOE/CF-0167 – Department of Energy FY 2021 Congressional Budget Request, Budget in Brief, February 2020. https://www.energy.gov/sites/default/files/2020/02/f72/doe-fy2021-budget-in-brief_0.pdf {{Webarchive|url=https://web.archive.org/web/20210718212001/https://www.energy.gov/sites/default/files/2020/02/f72/doe-fy2021-budget-in-brief_0.pdf |date=2021-07-18  }}</ref> About a quarter of this budget is directed to support ITER.

The size of the investments and time lines meant that fusion research was traditionally almost exclusively publicly funded. However, starting in the 2010s, the promise of commercializing a paradigm-changing [[low-carbon energy]] source began to attract a raft of companies and investors.<ref>{{Cite book|editor=Nuttall, William J. |title=Commercialising fusion energy : how small businesses are transforming big science|date=2020|publisher=Institute of Physics |isbn=978-0750327176|oclc=1230513895}}</ref> Over two dozen start-up companies attracted over one billion dollars from roughly 2000 to 2020, mainly from 2015, and a further three billion in funding and milestone related commitments in 2021,<ref>{{Cite book|last=Fusion Energy Sciences Advisory Committee|url=https://usfusionandplasmas.org/wp-content/themes/FESAC/FESAC_Report_2020_Powering_the_Future.pdf|title=Powering the Future: Fusion & Plasmas|publisher=Department of Energy Fusion Energy Sciences|year=2021|location=Washington|pages=ii|language=en}}</ref><ref>{{Cite web|last=Helman|first=Christopher|title=Fueled By Billionaire Dollars, Nuclear Fusion Enters A New Age|url=https://www.forbes.com/sites/christopherhelman/2022/01/02/fueled-by-billionaire-dollars-nuclear-fusion-enters-a-new-age/|access-date=2022-01-14|website=Forbes|language=en}}</ref> with investors including [[Jeff Bezos]], [[Peter Thiel]] and [[Bill Gates]], as well as institutional investors including [[Legal & General]], and energy companies including [[Equinor]], [[Eni]], [[Chevron Corporation|Chevron]],<ref name="Space Race">{{Cite web|last=Windridge|first=Melanie|title=The New Space Race Is Fusion Energy|url=https://www.forbes.com/sites/melaniewindridge/2020/10/07/the-new-space-race-is-fusion-energy/|access-date=2020-10-10|website=Forbes|language=en}}</ref> and the Chinese [[ENN Group]].<ref>{{Citation |last1=Pearson |first1=Richard J. |title=Review of approaches to fusion energy |date=2020 |url=http://dx.doi.org/10.1088/978-0-7503-2719-0ch2 |work=Commercialising Fusion Energy |access-date=2021-12-13 |publisher=IOP Publishing |doi=10.1088/978-0-7503-2719-0ch2 |isbn=978-0750327190 |s2cid=234561187 |last2=Takeda |first2=Shutaro}}</ref><ref>{{Citation |last1=Pearson |first1=Richard J. |title=Pioneers of commercial fusion |date=2020 |url=http://dx.doi.org/10.1088/978-0-7503-2719-0ch7 |work=Commercialising Fusion Energy |access-date=2021-12-13 |publisher=IOP Publishing |doi=10.1088/978-0-7503-2719-0ch7 |isbn=978-0750327190 |s2cid=234528929 |last2=Nuttall |first2=William J.}}</ref><ref name="Diffusion" /> In 2021, Commonwealth Fusion Systems (CFS) obtained $1.8 billion in scale-up funding, and Helion Energy obtained a half-billion dollars with an additional $1.7 billion contingent on meeting milestones.<ref name="Sets Sights">{{Cite web |title=White House Sets Sights on Commercial Fusion Energy |url=https://www.aip.org/fyi/2022/white-house-sets-sights-commercial-fusion-energy |access-date=2022-05-03 |website=www.aip.org |date=April 25, 2022 |language=en}}</ref>

Scenarios developed in the 2000s and early 2010s discussed the effects of the commercialization of fusion power on the future of human civilization.<ref name="Giant Step">{{cite web |last1=Lee |first1=Sing |last2=Saw |first2=Sor Heoh |title=Nuclear Fusion Energy – Mankind's Giant Step Forward |url=http://www.plasmafocus.net/IPFS/2010%20Papers/LSmankind.pdf |access-date=30 October 2014 |publisher=HPlasmafocus.net}}</ref> Using nuclear fission as a guide, these saw ITER and later [[DEMOnstration Power Station|DEMO]] as bringing online the first commercial reactors around 2050 and a rapid expansion after mid-century.<ref name="Giant Step" /> Some scenarios emphasized "fusion nuclear science facilities" as a step beyond ITER.<ref>{{Cite journal|last1=Kessel|first1=C. E.|last2=Blanchard|first2=J. P.|last3=Davis|first3=A.|last4=El-Guebaly|first4=L.|last5=Ghoniem|first5=N.|last6=Humrickhouse|first6=P. W.|last7=Malang|first7=S.|last8=Merrill|first8=B. J.|last9=Morley|first9=N. B.|last10=Neilson|first10=G. H.|last11=Rensink|first11=M. E.|date=2015-09-01|title=The Fusion Nuclear Science Facility, the Critical Step in the Pathway to Fusion Energy|url=https://doi.org/10.13182/FST14-953|journal=Fusion Science and Technology|volume=68|issue=2|pages=225–236|doi=10.13182/FST14-953|bibcode=2015FuST...68..225K |osti=1811772|s2cid=117842168|issn=1536-1055}}</ref><ref name="pilot plants">{{Cite journal |last1=Menard |first1=J. E. |last2=Brown |first2=T. |last3=El-Guebaly |first3=L. |last4=Boyer |first4=M. |last5=Canik |first5=J. |last6=Colling |first6=B. |last7=Raman |first7=R. |last8=Wang |first8=Z. |last9=Zhai |first9=Y. |last10=Buxton |first10=P. |last11=Covele |first11=B. |date=2016-10-01 |title=Fusion nuclear science facilities and pilot plants based on the spherical tokamak |url=https://iopscience.iop.org/article/10.1088/0029-5515/56/10/106023 |journal=Nuclear Fusion |volume=56 |issue=10 |pages=106023 |bibcode=2016NucFu..56j6023M |doi=10.1088/0029-5515/56/10/106023 |osti=1335165 |issn=0029-5515 |s2cid=125184562}}</ref> However, the economic obstacles to tokamak-based fusion power remain immense, requiring investment to fund prototype tokamak reactors<ref>{{Cite journal|last=Cardozo|first=N. J. Lopes|date=2019-02-04|title=Economic aspects of the deployment of fusion energy: the valley of death and the innovation cycle|journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences |volume=377|issue=2141|pages=20170444|doi=10.1098/rsta.2017.0444|pmid=30967058|bibcode=2019RSPTA.37770444C|s2cid=106411210|issn=1364-503X|doi-access=free}}</ref> and development of new supply chains,<ref>{{Cite journal|last=Surrey|first=E.|date=2019-02-04|title=Engineering challenges for accelerated fusion demonstrators|journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences|volume=377|issue=2141|pages=20170442|doi=10.1098/rsta.2017.0442|pmid=30967054|pmc=6365852|bibcode=2019RSPTA.37770442S|issn=1364-503X|doi-access=free}}</ref> a problem which will affect any kind of fusion reactor.<ref>{{Cite book |url=https://drive.google.com/file/d/1rXrzFQ83DL2q68UB3BjU2jdFVSRHxxBF/view |title=The Fusion Industry Supply Chain: Opportunities and Challenges |publisher=Fusion Industry Association |year=2023 |location=Washington, DC}}</ref> Tokamak designs appear to be labour-intensive,<ref>{{Cite journal|last1=Banacloche|first1=Santacruz|last2=Gamarra|first2=Ana R.|last3=Lechon|first3=Yolanda|last4=Bustreo|first4=Chiara|date=2020-10-15|title=Socioeconomic and environmental impacts of bringing the sun to earth: A sustainability analysis of a fusion power plant deployment |url=https://www.sciencedirect.com/science/article/pii/S0360544220315681|journal=Energy|language=en|volume=209|pages=118460|doi=10.1016/j.energy.2020.118460|bibcode=2020Ene...20918460B |s2cid=224952718|issn=0360-5442}}</ref> while the commercialization risk of alternatives like inertial fusion energy is high due to the lack of government resources.<ref>{{Cite journal|last=Koepke|first=M. E.|date=2021-01-25|title=Factors influencing the commercialization of inertial fusion energy|url= |journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences|language=en|volume=379|issue=2189|pages=20200020|doi=10.1098/rsta.2020.0020|issn=1364-503X|pmc=7741007|pmid=33280558|bibcode=2021RSPTA.37900020K}}</ref>

Scenarios since 2010 note computing and material science advances enabling multi-phase national or cost-sharing "Fusion Pilot Plants" (FPPs) along various technology pathways,<ref>{{Cite journal |last1=Menard |first1=J. E. |last2=Bromberg |first2=L. |last3=Brown |first3=T. |last4=Burgess |first4=T. |last5=Dix |first5=D. |last6=El-Guebaly |first6=L. |last7=Gerrity |first7=T. |last8=Goldston |first8=R. J. |last9=Hawryluk |first9=R. J. |last10=Kastner |first10=R. |last11=Kessel |first11=C. |date=2011-10-01 |title=Prospects for pilot plants based on the tokamak, spherical tokamak and stellarator |url=https://iopscience.iop.org/article/10.1088/0029-5515/51/10/103014 |journal=Nuclear Fusion |volume=51 |issue=10 |pages=103014 |bibcode=2011NucFu..51j3014M |doi=10.1088/0029-5515/51/10/103014 |issn=0029-5515 |s2cid=55781189}}</ref><ref name="pilot plants" /><ref name="Tokamak">{{Cite journal|last1=Hiwatari|first1=Ryoji|last2=Goto |first2=Takuya|date=2019-03-19|title=Assessment on Tokamak Fusion Power Plant to Contribute to Global Climate Stabilization in the Framework of Paris Agreement|journal=Plasma and Fusion Research |volume=14|pages=1305047|bibcode=2019PFR....1405047H|doi=10.1585/pfr.14.1305047|issn=1880-6821|doi-access=free}}</ref><ref>{{Cite book|last=((National Academies of Sciences, Engineering, and Medicine (U.S.). Committee on a Strategic Plan for U.S. Burning Plasma Research))|title=Final report of the Committee on a Strategic Plan for U.S. Burning Plasma Research|isbn=978-0309487443|location=Washington, DC|oclc=1104084761}}</ref><ref>{{Cite book|url=https://drive.google.com/file/d/1w0TKL_Jn0tKUBgUc8RC1s5fIOViH5pRK/view|title=A Community Plan for Fusion Energy and Discovery Plasma Sciences|publisher=American Physical Society Division of Plasma Physics Community Planning Process|year=2020|location=Washington, DC}}</ref><ref>{{Cite web|date=2020-04-07|title=US Plasma Science Strategic Planning Reaches Pivotal Phase|url=https://www.aip.org/fyi/2020/us-plasma-science-strategic-planning-reaches-pivotal-phase|access-date=2020-10-08|website=www.aip.org|language=en}}</ref> such as the UK [[Spherical Tokamak for Energy Production]], within the 2030–2040 time frame.<ref>{{Cite news|last1=Asmundssom|first1=Jon|last2=Wade|first2=Will|title=Nuclear Fusion Could Rescue the Planet from Climate Catastrophe|work=Bloomberg|url=https://www.bloomberg.com/news/features/2019-09-28/startups-take-aim-at-nuclear-fusion-energy-s-biggest-challenge|access-date=2020-09-21}}</ref><ref>{{Cite news|last=Michaels|first=Daniel|date=2020-02-06|title=Fusion Startups Step In to Realize Decades-Old Clean Power Dream|language=en-US|work=[[The Wall Street Journal]]|url=https://www.wsj.com/articles/fusion-startups-step-in-to-realize-decades-old-clean-power-dream-11581001383|access-date=2020-10-08|issn=0099-9660}}</ref><ref name="Early Markets">{{Cite journal|last1=Handley|first1=Malcolm C.|last2=Slesinski|first2=Daniel|last3=Hsu|first3=Scott C.|date=2021-07-10|title=Potential Early Markets for Fusion Energy|url=http://dx.doi.org/10.1007/s10894-021-00306-4|journal=Journal of Fusion Energy|volume=40|issue=2|page=18|doi=10.1007/s10894-021-00306-4|issn=0164-0313|arxiv=2101.09150|bibcode=2021JFuE...40...18H |s2cid=231693147}}</ref> Notably, in June 2021, General Fusion announced it would accept the UK government's offer to host the world's first substantial [[Public–private partnership|public-private partnership]] fusion demonstration plant, at [[Culham Centre for Fusion Energy]].<ref>{{Cite journal|last=Ball|first=Philip|date=2021-11-17|title=The chase for fusion energy|journal=Nature|language=en|volume=599|issue=7885|pages=352–366|doi=10.1038/d41586-021-03401-w|pmid=34789909|s2cid=244346561|doi-access=free}}</ref> The plant will be constructed from 2022 to 2025 and is intended to lead the way for commercial pilot plants in the late 2025s. The plant will be 70% of full scale and is expected to attain a stable plasma of 150 million degrees.<ref>{{Cite web|date=2021-06-16|title=A Historic Decision: To Demonstrate Practical Fusion at Culham|url=https://generalfusion.com/2021/06/a-historic-decision-to-demonstrate-practical-fusion-at-culham/|access-date=2021-06-18|website=General Fusion|language=en-US}}</ref> In the United States, cost-sharing public-private partnership FPPs appear likely,<ref>{{Cite web|last=Holland|first=Andrew| author-link = Andrew Holland| date=2021-07-15|title=Congress Would Fund Fusion Cost-Share Program in Committee-Passed Appropriations Bill|url=https://www.fusionindustryassociation.org/post/house-energy-water-subcommittee-includes-cost-share-program-in-their-passed-appropriation-bill|access-date=2021-07-16|website=Fusion Industry Assn|language=en|archive-date=2023-04-20 |archive-url=https://web.archive.org/web/20230420002948/https://www.fusionindustryassociation.org/post/house-energy-water-subcommittee-includes-cost-share-program-in-their-passed-appropriation-bill|url-status=dead}}</ref> and in 2022 the DOE announced a new Milestone-Based Fusion Development Program as the centerpiece of its Bold Decadal Vision for Commercial Fusion Energy,<ref>{{Cite web |last=Sailer |first=Sandy |date=2023-05-31 |title=Department of Energy Announces Milestone Public-Private Partnership Awards |url=https://www.fusionindustryassociation.org/department-of-energy-announces-milestone-public-private-partnership-awards/ |access-date=2023-06-01 |website=Fusion Industry Association |language=en-US}}</ref> which envisages private sector-led teams delivering FPP pre-conceptual designs, defining technology roadmaps, and pursuing the R&D necessary to resolve critical-path scientific and technical issues towards an FPP design.<ref>{{Cite journal |last=Hsu |first=Scott C. |date=2023-05-05 |title=U.S. Fusion Energy Development via Public-Private Partnerships |journal=Journal of Fusion Energy |volume=42 |issue=1 |page=12 |doi=10.1007/s10894-023-00357-9 |s2cid=258489130 |issn=0164-0313|doi-access=free |bibcode=2023JFuE...42...12H }}</ref> Compact reactor technology based on such demonstration plants may enable commercialization via a fleet approach from the 2030s<ref>{{Cite journal|last1=Spangher|first1=Lucas|last2=Vitter|first2=J. Scott|last3=Umstattd|first3=Ryan|date=2019|title=Characterizing fusion market entry via an agent-based power plant fleet model|journal=Energy Strategy Reviews|volume=26|pages=100404|doi=10.1016/j.esr.2019.100404|issn=2211-467X|doi-access=free|bibcode=2019EneSR..2600404S }}</ref> if early markets can be located.<ref name="Early Markets" />

The widespread adoption of non-nuclear renewable energy has transformed the energy landscape. Such renewables are projected to supply 74% of global energy by 2050.<ref>{{Cite web|title=Global Energy Perspectives 2019|url=https://www.mckinsey.com/~/media/mckinsey/industries/oil%20and%20gas/our%20insights/global%20energy%20perspective%202019/mckinsey-energy-insights-global-energy-perspective-2019_reference-case-summary.ashx|website=Energy Insights- Mckinsey}}</ref> The steady fall of renewable energy prices challenges the economic competitiveness of fusion power.<ref name="Energy Mix">{{Cite journal|last1=Nicholas|first1=T. E. G.|last2=Davis|first2=T. P.|last3=Federici|first3=F.|last4=Leland|first4=J. E.|last5=Patel|first5=B. S.|last6=Vincent|first6=C.|last7=Ward|first7=S. H.|date=February 2021|title=Re-examining the Role of Nuclear Fusion in a Renewables-Based Energy Mix|journal=Energy Policy|volume=149|pages=112043|arxiv=2101.05727|doi=10.1016/j.enpol.2020.112043|bibcode=2021EnPol.14912043N |s2cid=230570595}}</ref>

[[File:20201019 Levelized Cost of Energy (LCOE, Lazard) - renewable energy.svg|thumb|upright=1.5|Levelized cost of energy (LCOE) for various sources of energy including wind, solar and nuclear energy<ref name=LazardLCOE_2024>{{cite web |title=Lazard LCOE Levelized Cost Of Energy+ |url=https://www.lazard.com/media/xemfey0k/lazards-lcoeplus-june-2024-_vf.pdf |publisher=Lazard |archive-url=https://web.archive.org/web/20240828224744/https://www.lazard.com/media/xemfey0k/lazards-lcoeplus-june-2024-_vf.pdf |archive-date=28 August 2024 |page=16 |date=June 2024 |url-status=live}}</ref>]]

Some economists suggest fusion power is unlikely to match other [[renewable energy]] costs.<ref name="Energy Mix" /> Fusion plants are expected to face large start up and [[capital cost]]s. Moreover, operation and maintenance are likely to be costly.<ref name="Energy Mix" /> While the costs of the [[China Fusion Engineering Test Reactor]] are not well known, an EU DEMO fusion concept was projected to feature a [[levelized cost of energy]] (LCOE) of $121/MWh.<ref>{{Cite journal|date=2018-06-01|title=Approximation of the economy of fusion energy|journal=Energy|language=en|volume=152|pages=489–497|doi=10.1016/j.energy.2018.03.130|issn=0360-5442|doi-access=free|last1=Entler|first1=Slavomir|last2=Horacek|first2=Jan|last3=Dlouhy|first3=Tomas|last4=Dostal|first4=Vaclav|bibcode=2018Ene...152..489E }}</ref>

Fuel costs are low, but economists suggest that the energy cost for a one-gigawatt plant would increase by $16.5 per MWh for every $1 billion increase in the capital investment in construction. There is also the risk that easily obtained lithium will be used up making batteries. Obtaining it from seawater would be very costly and might require more energy than the energy that would be generated.<ref name="Energy Mix" />

In contrast, [[Renewable energy|renewable]] levelized cost of energy estimates are substantially lower. For instance, the 2019 levelized cost of energy of [[solar energy]] was estimated to be $40-$46/MWh, [[Onshore wind farm|on shore wind]] was estimated at $29-$56/MWh, and [[Offshore wind power|offshore wind]] was approximately $92/MWh.<ref>{{Cite web|title=Levelized Cost of Energy and Levelized Cost of Storage 2019|url=http://www.lazard.com/perspective/levelized-cost-of-energy-and-levelized-cost-of-storage-2019/|access-date=2021-06-01|website=Lazard.com|language=en|archive-date=2023-02-19 |archive-url=https://web.archive.org/web/20230219103421/http://www.lazard.com/perspective/levelized-cost-of-energy-and-levelized-cost-of-storage-2019/|url-status=dead}}</ref>

However, fusion power may still have a role filling energy gaps left by renewables,<ref name="Early Markets" /><ref name="Energy Mix" /> depending on how administration priorities for energy and environmental justice influence the market.<ref name="Sets Sights" /> In the 2020s, socioeconomic studies of fusion that began to consider these factors emerged,<ref>{{Cite journal |last1=Griffiths |first1=Thomas |last2=Pearson |first2=Richard |last3=Bluck |first3=Michael |last4=Takeda |first4=Shutaro |date=2022-10-01 |title=The commercialisation of fusion for the energy market: a review of socio-economic studies |journal=Progress in Energy |volume=4 |issue=4 |pages=042008 |doi=10.1088/2516-1083/ac84bf |bibcode=2022PrEne...4d2008G |s2cid=251145811 |issn=2516-1083|doi-access=free }}</ref> and in 2022 EUROFusion launched its Socio-Economic Studies and Prospective Research and Development strands to investigate how such factors might affect commercialization pathways and timetables.<ref>{{Cite journal |last1=Kembleton |first1=R. |last2=Bustreo |first2=C. |date=2022 |title=Prospective research and development for fusion commercialisation |journal=Fusion Engineering and Design |volume=178 |pages=113069 |doi=10.1016/j.fusengdes.2022.113069 |s2cid=247338079 |issn=0920-3796|doi-access=free |bibcode=2022FusED.17813069K }}</ref> Similarly, in April 2023 Japan announced a national strategy to industrialise fusion.<ref>{{Cite web |last=Otake |first=Tomoko |date=2023-04-14 |title=Japan adopts national strategy on nuclear fusion as competition intensifies |url=https://www.japantimes.co.jp/news/2023/04/14/national/japan-national-strategy-nuclear-fusion/ |access-date=2023-04-19 |website=The Japan Times |language=en-US}}</ref> Thus, fusion power may work in tandem with other renewable energy sources rather than becoming the primary energy source.<ref name="Energy Mix" /> In some applications, fusion power could provide the base load, especially if including integrated thermal storage and cogeneration and considering the potential for retrofitting coal plants.<ref name="Early Markets" /><ref name="Energy Mix" />

== Regulation ==
As fusion pilot plants move within reach, legal and regulatory issues must be addressed.<ref>{{Cite journal|last=Holland|first=Andrew|date=2020-11-13|title=Political and commercial prospects for inertial fusion energy|journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences |volume=378|issue=2184|pages=20200008|doi=10.1098/rsta.2020.0008|pmid=33040662|bibcode=2020RSPTA.37800008H|s2cid=222277887|doi-access=free}}</ref> In September 2020, the United States [[National Academy of Sciences]] consulted with private fusion companies to consider a national pilot plant. The following month, the United States Department of Energy, the [[Nuclear Regulatory Commission]] (NRC) and the [[Fusion Industry Association]] co-hosted a public forum to begin the process.<ref name="Space Race" /> In November 2020, the [[International Atomic Energy Agency]] (IAEA) began working with various nations to create safety standards<ref name="Safety in Fusion">{{Cite web|date=2021-05-28|title=Safety in Fusion|url=https://www.iaea.org/fusion-energy/safety-in-fusion|access-date=2021-06-01|website=www.iaea.org|language=en}}</ref> such as dose regulations and [[radioactive waste]] handling.<ref name="Safety in Fusion" /> In January and March 2021, NRC hosted two public meetings on regulatory frameworks.<ref>{{Cite web|last=Slesinski|first=Daniel|date=2021-01-28|title=NRC Hosts Virtual Public Meeting on Developing Options for a Regulatory Framework for Fusion Energy|url=https://www.fusionindustryassociation.org/post/nrc-hosts-virtual-public-meeting-on-developing-options-for-a-regulatory-framework-for-fusion-energy|access-date=2021-02-14|website=Fusion Industry Assn|language=en}}</ref><ref>{{Cite web|last=Slesinski|first=Daniel|date=2021-03-30|title=NRC Hosts Second Virtual Public Meeting on Developing a Regulatory Framework for Fusion Energy|url=https://www.fusionindustryassociation.org/post/nrc-hosts-second-virtual-public-meeting-on-developing-a-regulatory-framework-for-fusion|access-date=2021-04-10|website=Fusion Industry Assn|language=en}}</ref> A public-private cost-sharing approach was endorsed in the 27 December H.R.133 Consolidated Appropriations Act, 2021, which authorized $325 million over five years for a partnership program to build fusion demonstration facilities, with a 100% match from private industry.<ref>{{Cite web|last=Holland|first=Andrew|date=2021-01-05|title=Fusion Legislation Signed into Law|url=https://www.fusionindustryassociation.org/post/fusion-legislation-signed-into-law|access-date=2021-02-14|website=Fusion Industry Assn|language=en}}</ref>

Subsequently, the UK Regulatory Horizons Council published a report calling for a fusion regulatory framework by early 2022<ref>{{Cite web|last=Windridge|first=Melanie|title=U.K Serious About Fusion: New Report On Regulation Recommends Proportionate, Agile Approach|url=https://www.forbes.com/sites/melaniewindridge/2021/06/02/uk-serious-about-fusion-new-report-on-regulation-recommends-proportionate-agile-approach/|access-date=2021-06-03|website=Forbes|language=en}}</ref> in order to position the UK as a global leader in commercializing fusion power.<ref>{{Cite web|last=Holland|first=Andrew|date=2021-06-01|title=UK Regulatory Horizons Council Issues Report on Fusion Energy Regulation|url=https://www.fusionindustryassociation.org/post/uk-s-regulatory-horizons-council-issues-report-on-fusion-energy-regulation|access-date=2021-06-21|website=Fusion Industry Assn|language=en|archive-date=2023-04-20 |archive-url=https://web.archive.org/web/20230420002958/https://www.fusionindustryassociation.org/post/uk-s-regulatory-horizons-council-issues-report-on-fusion-energy-regulation|url-status=dead}}</ref> This call was met by the UK government publishing in October 2021 both its ''Fusion Green Paper'' and its ''Fusion Strategy'', to regulate and commercialize fusion, respectively.<ref>{{Cite book |url=https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1022540/towards-fusion-energy-uk-government-fusion-strategy.pdf |title=Towards Fusion Energy: The UK Government's Fusion Strategy |publisher=UK Government, Department for Business, Energy, & Industrial Strategy |year=2021 |location=London, UK |language=En}}</ref><ref>{{Cite web|title=Government sets out vision for UK's rollout of commercial fusion energy|url=https://www.gov.uk/government/news/government-sets-out-vision-for-uks-rollout-of-commercial-fusion-energy|access-date=2021-10-15|website=GOV.UK|language=en}}</ref><ref>{{Cite web|title=UK government publishes fusion strategy – Nuclear Engineering International|url=https://www.neimagazine.com/news/newsuk-government-publishes-fusion-strategy-9129061|access-date=2021-10-15|website=www.neimagazine.com|date=October 5, 2021 }}</ref> Then, in April 2023, in a decision likely to influence other nuclear regulators, the NRC announced in a unanimous vote that fusion energy would be regulated not as fission but under the same regulatory regime as particle accelerators.<ref>{{Cite web |last=Holland |first=Andrew |date=2023-04-14 |title=NRC Decision Separates Fusion Energy Regulation from Nuclear Fission |url=https://www.fusionindustryassociation.org/post/nrc-decision-separates-fusion-energy-regulation-from-nuclear-fission |access-date=2023-04-19 |website=Fusion Industry Assn |language=en}}</ref>

Then, in October 2023 the UK government, in enacting the Energy Act 2023, made the UK the first country to legislate for fusion separately from fission, to support planning and investment, including the UK's planned prototype fusion power plant for 2040; [[Spherical Tokamak for Energy Production|STEP]]<ref>{{Cite web |title=New laws passed to bolster energy security and deliver net zero |url=https://www.gov.uk/government/news/new-laws-passed-to-bolster-energy-security-and-deliver-net-zero |access-date=2023-11-10 |website=GOV.UK |language=en}}</ref> the UK is working with Canada and Japan in this regard.<ref>{{Cite web |title=Agile Nations: UK, Japan and Canada joint recommendations on fusion energy |url=https://www.gov.uk/government/publications/agile-nations-uk-japan-and-canada-joint-recommendations-on-fusion-energy |access-date=2024-03-20 |website=GOV.UK |language=en}}</ref> Meanwhile, in February 2024 the US House of Representatives passed the Atomic Energy Advancement Act, which includes the Fusion Energy Act, which establishes a regulatory framework for fusion energy systems.<ref>{{Cite web |date=2024-02-29 |title=Fusion Caucus Celebrates House Passage of Bipartisan Fusion Energy Act |url=https://beyer.house.gov/news/documentsingle.aspx?DocumentID=6086 |access-date=2024-03-01 |website=U.S. Representative Don Beyer |language=en}}</ref>

== Geopolitics ==
Given the potential of fusion to transform the world's [[energy industry]] and mitigate [[climate change]],<ref name="regulation">{{Cite web|last=Holland|first=Andrew|title=Fusion energy needs smart federal government regulation|url=https://www.washingtontimes.com/news/2020/oct/6/fusion-energy-needs-smart-federal-government-regul/|access-date=2020-10-10|website=The Washington Times|language=en-US}}</ref><ref>{{Cite web|last=Turrell|first=Arthur|date=2021-08-28|title=The race to give nuclear fusion a role in the climate emergency|url=http://www.theguardian.com/environment/2021/aug/28/the-race-to-give-nuclear-fusion-a-role-in-the-climate-emergency|access-date=2022-02-15|website=the Guardian|language=en}}</ref> fusion science has traditionally been seen as an integral part of peace-building [[science diplomacy]].<ref name="quest">{{Cite book|author1=Clery, Daniel|title=A piece of the sun: the quest for fusion energy |date=2014|isbn=978-1468310412|location=New York |publisher=Overlook Duckworth |oclc=1128270426}}</ref><ref name="ITER">{{Cite book|last=Claessens, Michel |title=ITER: the giant fusion reactor: bringing a sun to Earth|date= 2019|isbn=978-3030275815|location=Cham |publisher=Springer |oclc=1124925935}}</ref> However, technological developments<ref>{{Cite news|date=2018-04-18|title=Will China beat the world to nuclear fusion and clean energy?|language=en-GB |publisher=BBC News |work=China Blog |url=https://www.bbc.com/news/blogs-china-blog-43792655|access-date=2020-10-12}}</ref> and private sector involvement has raised concerns over intellectual property, regulatory administration, global leadership;<ref name="regulation" /> equity, and potential weaponization.<ref name="Diffusion">{{Cite journal|last1=Carayannis|first1=Elias G.|last2=Draper|first2=John|last3=Iftimie|first3=Ion A.|date=2020|title=Nuclear Fusion Diffusion: Theory, Policy, Practice, and Politics Perspectives|url=https://ieeexplore.ieee.org/document/9078039|journal=IEEE Transactions on Engineering Management|volume=69 |issue=4 |pages=1237–1251|doi=10.1109/TEM.2020.2982101|s2cid=219001461|issn=0018-9391}}</ref><ref name="Urgent Action">{{Cite journal|last1=Carayannis|first1=Elias G.|last2=Draper|first2=John|last3=Bhaneja|first3=Balwant|date=2020-10-02|title=Towards Fusion Energy in the Industry 5.0 and Society 5.0 Context: Call for a Global Commission for Urgent Action on Fusion Energy|journal=Journal of the Knowledge Economy|volume=12|issue=4|pages=1891–1904|language=en|doi=10.1007/s13132-020-00695-5|issn=1868-7873|s2cid=222109349|doi-access=free}}</ref> These challenge ITER's peace-building role and led to calls for a global commission.<ref name="Urgent Action" /><ref>{{Cite journal|last1=Carayannis|first1=Elias G.|last2=Draper|first2=John|date=2021-04-22|title=The place of peace in the ITER machine assembly launch: Thematic analysis of the political speeches in the world's largest science diplomacy experiment.|url=http://dx.doi.org/10.1037/pac0000559|journal=Peace and Conflict: Journal of Peace Psychology|volume=27|issue=4|pages=665–668|doi=10.1037/pac0000559|s2cid=235552703|issn=1532-7949}}</ref> Fusion power significantly contributing to climate change by 2050 seems unlikely without substantial breakthroughs and a space race mentality emerging,<ref name="Tokamak" /><ref>{{Cite journal|last1=Gi|first1=Keii|last2=Sano|first2=Fuminori|last3=Akimoto|first3=Keigo|last4=Hiwatari|first4=Ryoji|last5=Tobita|first5=Kenji|date=2020|title=Potential contribution of fusion power generation to low-carbon development under the Paris Agreement and associated uncertainties|journal=Energy Strategy Reviews |language=en|volume=27|pages=100432|doi=10.1016/j.esr.2019.100432|doi-access=free|bibcode=2020EneSR..2700432G }}</ref> but a contribution by 2100 appears possible, with the extent depending on the type and particularly cost of technology pathways.<ref>{{Cite journal |last1=Nicholas |first1=T. E. G. |last2=Davis |first2=T. P. |last3=Federici |first3=F. |last4=Leland |first4=J. |last5=Patel |first5=B. S. |last6=Vincent |first6=C. |last7=Ward |first7=S. H. |date=2021 |title=Re-examining the role of nuclear fusion in a renewables-based energy mix |url=http://dx.doi.org/10.1016/j.enpol.2020.112043 |journal=Energy Policy |volume=149 |pages=112043 |arxiv=2101.05727 |doi=10.1016/j.enpol.2020.112043 |bibcode=2021EnPol.14912043N |issn=0301-4215 |s2cid=230570595}}</ref><ref>{{Cite journal|last1=Carayannis|first1=Elias|last2=Draper|first2=John|last3=Crumpton|first3=Charles|date=2022|title=Reviewing fusion energy to address climate change by 2050|url=https://www.scribd.com/document/557471226/Reviewing-Fusion-Energy-to-Address-Climate-Change-by-2050-by-Elias-G-Carayannis-John-Draper-and-Charles-David-Crumpton|journal=Journal of Energy and Development|volume=47|issue=1}}</ref>

Developments from late 2020 onwards have led to talk of a "new space race" with multiple entrants, pitting the US against China<ref name=5big>{{Cite journal|last=Clynes|first=Tom|date=2020|title=5 Big ideas for fusion power: Startups, universities, and major companies are vying to commercialize a nuclear fusion reactor|url=https://ieeexplore.ieee.org/document/8976899|journal=IEEE Spectrum|volume=57|issue=2|pages=30–37|doi=10.1109/MSPEC.2020.8976899|s2cid=211059641|issn=0018-9235}}</ref> and the UK's [[Spherical Tokamak for Energy Production|STEP]] FPP,<ref>{{Cite web|date=2021-04-14|title=National Academies calls for a fusion pilot plant|url=https://thebulletin.org/2021/04/national-academies-calls-for-a-fusion-pilot-plant/|access-date=2021-04-15|website=Bulletin of the Atomic Scientists|language=en-US}}</ref><ref>{{Cite web|date=2021-07-13|title=US must make an infrastructure investment in fusion energy|url=https://www.washingtonexaminer.com/opinion/op-eds/us-must-make-an-infrastructure-investment-in-fusion-energy|access-date=2021-07-16|website=Washington Examiner|language=en}}</ref> with China now outspending the US and threatening to leapfrog US technology.<ref>{{Cite web |last=Nilsen |first=Angela Dewan, Ella |date=2024-09-19 |title=The US led on nuclear fusion for decades. Now China is in position to win the race |url=https://edition.cnn.com/2024/09/19/climate/nuclear-fusion-clean-energy-china-us/index.html?mc_cid=d722362adc&mc_eid=98f2d233a7 |access-date=2024-09-30 |website=CNN |language=en}}</ref> On 24 September 2020, the United States House of Representatives approved a research and commercialization program. The Fusion Energy Research section incorporated a milestone-based, cost-sharing, [[public-private partnership]] program modeled on [[NASA]]'s COTS program, which launched the commercial [[space industry]].<ref name="Space Race" /> In February 2021, the National Academies published ''Bringing Fusion to the U.S. Grid'', recommending a market-driven, cost-sharing plant for 2035–2040,<ref>{{Cite web|title=An aggressive market-driven model for US fusion power development|url=https://news.mit.edu/2021/aggressive-market-driven-model-us-fusion-power-development-0224|access-date=2021-02-26|website=MIT News {{!}} Massachusetts Institute of Technology|date=February 24, 2021 |language=en}}</ref><ref>{{Cite web|last1=Cho |first1=Adrian |date=2021-02-19|title=Road map to U.S. fusion power plant comes into clearer focus – sort of|url=https://www.science.org/content/article/road-map-us-fusion-power-plant-comes-clearer-focus-sort|access-date=2021-03-06|website=Science |language=en}}</ref><ref>{{Cite journal |last=Kramer |first=David |date=2021-03-10|title=Academies urge public–private effort to build a pilot fusion-power plant |journal=Physics Today |volume= 2021|issue=2 |pages= 0310a|language=en|doi=10.1063/PT.6.2.20210310a|s2cid=243296520 |doi-access=free|bibcode=2021PhT..2021b.310. }}</ref> and the launch of the Congressional Bipartisan Fusion Caucus followed.<ref>{{Cite web |date=2021-02-19 |title=FIA Congratulates Congressional Bipartisan Fusion Caucus |url=https://www.fusionindustryassociation.org/post/fia-congratulates-congressional-bipartisan-fusion-caucus |access-date=2021-02-26 |website=Fusion Industry Association |language=en-us}}</ref>

In December 2020, an independent expert panel reviewed [[EUROfusion]]'s design and R&D work on DEMO, and EUROfusion confirmed it was proceeding with its Roadmap to Fusion Energy, beginning the conceptual design of DEMO in partnership with the European fusion community, suggesting an EU-backed machine had entered the race.<ref>{{Cite web|last=Vries|first=Gieljan de|title=Expert panel approves next DEMO design phase|url=https://www.euro-fusion.org/news/2020/december/expert-panel-approves-next-demo-design-phase/|access-date=2021-02-16|website=www.euro-fusion.org|date=December 15, 2020 |language=en}}</ref>

In October 2023, the UK-oriented Agile Nations group announced a fusion working group.<ref>{{Cite web |title=US, Japan Team Up for Commercialization of Fusion Energy {{!}} Rigzone |url=https://www.rigzone.com/news/us_japan_team_up_for_commercialization_of_fusion_energy-15-apr-2024-176406-article/ |access-date=2024-07-03 |website=www.rigzone.com}}</ref> One month later, the UK and the US announced a bilateral partnership to accelerate fusion energy. Then, in December 2023 at [[2023 United Nations Climate Change Conference|COP28]] the US announced a US global strategy to commercialize fusion energy.<ref>{{Cite web |date=2023-12-05 |title=At COP28, John Kerry unveils nuclear fusion strategy as a source of clean energy |url=https://apnews.com/article/fusion-nuclear-john-kerry-cop28-climate-power-energy-40ffa257eae528163f68554368cacfee |access-date=2023-12-08 |website=AP News |language=en}}</ref> Then, in April 2024, Japan and the US announced a similar partnership,<ref>{{Cite news |last1=Renshaw |first1=Jarrett |last2=Gardner |first2=Timothy |date=10 April 2024 |title=US, Japan announce partnership to accelerate nuclear fusion |url=https://www.reuters.com/business/energy/us-japan-announce-joint-partnership-accelerate-nuclear-fusion-sources-2024-04-10/ |work=Reuters}}</ref> and in May of the same year, the G7 announced a G7 Working Group on Fusion Energy to promote international collaborations to accelerate the development of commercial energy and promote R&D between countries, as well as rationalize fusion regulation.<ref>{{Cite web |last=Caroline |date=2024-04-30 |title=G7 Puts Fusion Forward At The Climate, Energy And Environment Ministers' Meeting |url=https://www.fusionindustryassociation.org/g7-puts-fusion-forward-at-the-climate-energy-and-environment-ministers-meeting/ |access-date=2024-05-11 |website=Fusion Industry Association |language=en-US}}</ref> Later the same year, the US partnered with the IAEA to launch the [https://usionenergysolutionstaskforce.org Fusion Energy Solutions Taskforce], to collaboratively crowdsource ideas to accelerate commercial fusion energy, in line with the US COP28 statement.

Specifically to resolve the tritium supply problem, in February 2024, the UK ([[United Kingdom Atomic Energy Authority|UKAEA]]) and Canada ([[Canadian Nuclear Laboratories Research Facilities|Canadian Nuclear Laboratories]]) announced an agreement by which Canada could refurbish its [[CANDU reactor|Candu]] deuterium-uranium tritium-generating heavywater nuclear plants and even build new ones, guaranteeing a supply of tritium into the 2070s, while the UKAEA would test breeder materials and simulate how tritium could be captured, purified, and injected back into the fusion reaction.<ref>{{Cite web |title=UK and Canada team up to solve nuclear fusion fuel shortage |url=https://sciencebusiness.net/news/uk-and-canada-team-solve-nuclear-fusion-fuel-shortage |access-date=2024-05-11 |website=Science{{!}}Business |language=en}}</ref>

In 2024, both South Korea and Japan announced major initiatives to accelerate their national fusion strategies, by building electricity-generating public-private fusion plants in the 2030s, aiming to begin operations in the 2040s and 2030s respectively.<ref>{{Cite web |date=2024-07-24 |title=Gov't to chase 'artificial sun' with $866 million investment in nuclear fusion reactor development |url=https://koreajoongangdaily.joins.com/news/2024-07-24/business/economy/Govt-to-chase-artificial-sun-with-866-million-investment-in-nuclear-fusion-reactor-development/2097463 |access-date=2024-07-27 |website=koreajoongangdaily.joins.com |language=en}}</ref><ref>{{Cite web |date=2024-07-19 |title=核融合発電、30年代実証へ国家戦略改定 高市早苗経済安全保障相が表明 |url=https://www.nikkei.com/article/DGXZQOUA192KS0Z10C24A7000000/ |access-date=2024-07-27 |website=日本経済新聞 |language=ja}}</ref>

== Advantages ==
Fusion power promises to provide more energy for a given weight of fuel than any fuel-consuming energy source currently in use.<ref>{{cite web |author=Heeter |first=Robert F. |display-authors=etal |title=Conventional Fusion FAQ Section 2/11 (Energy) Part 2/5 (Environmental) |url=http://fusedweb.llnl.gov/FAQ/section2-energy/part2-enviro.txt |url-status=dead |archive-url=https://web.archive.org/web/20010303051913/http://fusedweb.llnl.gov/FAQ/section2-energy/part2-enviro.txt |archive-date=3 March 2001 |access-date=30 October 2014 |publisher=Fused.web.llnl.gov}}</ref> The fuel (primarily [[deuterium]]) exists abundantly in the ocean: about 1 in 6500 hydrogen atoms in seawater is deuterium.<ref>{{cite web |author=Stadermann |first=Frank J. |title=Relative Abundances of Stable Isotopes |url=http://presolar.wustl.edu/work/abundances.html |archive-url=https://web.archive.org/web/20110720122226/http://presolar.wustl.edu/work/abundances.html |archive-date=2011-07-20 |publisher=Laboratory for Space Sciences, Washington University in St. Louis}}</ref> Although this is only about 0.015%, seawater is plentiful and easy to access, implying that fusion could supply the world's energy needs for millions of years.<ref>{{cite web |last1=Ongena |first1=J. |last2=Van Oost |first2=G. |title=Energy for Future Centuries |url=http://www.agci.org/dB/PDFs/03S2_MMauel_SafeFusion%3F.pdf |url-status=dead |archive-url=https://web.archive.org/web/20110727135814/http://www.agci.org/dB/PDFs/03S2_MMauel_SafeFusion?.pdf |archive-date=2011-07-27 |publisher=Laboratorium voor Plasmafysica – Laboratoire de Physique des Plasmas Koninklijke Militaire School – École Royale Militaire; Laboratorium voor Natuurkunde, Universiteit Gent |pages=Section III.B. and Table VI}}</ref><ref>{{cite web|url=http://www.eps.org/about-us/position-papers/fusion-energy/|archive-url=https://web.archive.org/web/20081008001417/http://www.eps.org/about-us/position-papers/fusion-energy/|archive-date=2008-10-08|title=The importance of European fusion energy research|publisher=The European Physical Society|author=EPS Executive Committee}}</ref>

First generation fusion plants are expected to use the deuterium-tritium fuel cycle. This will require the use of lithium for breeding of the tritium. It is not known for how long global lithium supplies will suffice to supply this need as well as those of the battery and metallurgical industries. It is expected that second generation plants will move on to the more formidable deuterium-deuterium reaction. The deuterium-helium-3 reaction is also of interest, but the light helium isotope is practically non-existent on Earth. It is thought to exist in useful quantities in the [[lunar regolith]], and is abundant in the atmospheres of the gas giant planets.

Fusion power could be used for so-called "deep space" propulsion within the solar system<ref>{{Cite news|title=Space propulsion {{!}} Have fusion, will travel|url=http://www.iter.org/newsline/-/3303|access-date=2021-06-21|website=ITER|language=en}}</ref><ref>{{Cite web|last=Holland|first=Andrew|date=2021-06-15|title=Funding for Fusion for Space Propulsion|url=https://www.fusionindustryassociation.org/post/fia-proposes-funding-for-fusion-for-space-propulsion|access-date=2021-06-21|website=Fusion Industry Assn|language=en|archive-date=2023-04-20 |archive-url=https://web.archive.org/web/20230420002956/https://www.fusionindustryassociation.org/post/fia-proposes-funding-for-fusion-for-space-propulsion|url-status=dead}}</ref> and for [[interstellar space]] exploration where solar energy is not available, including via [[Antimatter-catalyzed nuclear pulse propulsion|antimatter-fusion]] hybrid drives.<ref>{{Cite book|last1=Schulze|first1=Norman R. |title=Fusion energy for space missions in the 21st century|last2=United States|last3=National Aeronautics and Space Administration|last4=Scientific and Technical Information Program|date=1991|publisher=National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Program; [For sale by the National Technical Information Service [distributor|location=Washington, DC; Springfield, Va.|language=en|oclc=27134218}}</ref><ref>{{Cite book |chapter=Principles of Fusion Energy Utilization in Space Propulsion|date=1995-01-01|url=https://arc.aiaa.org/doi/10.2514/5.9781600866357.0001.0046 |title=Fusion Energy in Space Propulsion|pages=1–46|series=Progress in Astronautics and Aeronautics|publisher=American Institute of Aeronautics and Astronautics|doi=10.2514/5.9781600866357.0001.0046|isbn=978-1563471841|access-date=2020-10-11 }}</ref>

===Helium production===
{{See also|Helium production in the United States}}
[[Deuterium–tritium fusion]] produces [[helium]] as a [[by-product]].<ref>{{Cite web|url=https://www.energy.gov/science/doe-explainsfusion-reactions|title=DOE Explains...Fusion Reactions|website=Energy.gov}}</ref>

== Disadvantages ==
Fusion power has a number of disadvantages. Because 80 percent of the energy in any reactor fueled by deuterium and tritium appears in the form of neutron streams, such reactors share many of the drawbacks of fission reactors. This includes the production of large quantities of [[#Radioactive waste|radioactive waste]] and serious radiation damage to reactor components. Additionally, naturally occurring tritium is extremely rare. While the hope is that fusion reactors can breed their own tritium, tritium self-sufficiency is extremely challenging, not least because tritium is difficult to contain (tritium has leaked from 48 of 65 nuclear sites in the US<ref>
{{Cite web|url=https://www.nbcnews.com/id/wbna43475479|title=Radioactive tritium leaks found at 48 US nuke sites|last=Donn|first=Jeff|date=2011-06-21|access-date=2023-07-04|archive-url=https://web.archive.org/web/20201111214625/https://www.nbcnews.com/id/wbna43475479|archive-date=2020-11-11|publisher=[[NBC News]] |language=en-US}}</ref>). In any case the reserve and start-up tritium inventory requirements are likely to be unacceptably large.<ref name="TritiumSelfSufficiency_Abdou">{{cite journal |last1=Abdou |first1=M. |display-authors=et al |year=2020 |title=Physics and technology considerations for the deuterium-tritium fuel cycle and conditions for tritium fuel self sufficiency |url=https://iopscience.iop.org/article/10.1088/1741-4326/abbf35 |journal=Nuclear Fusion |volume=61 |issue=1 |page=013001 |doi=10.1088/1741-4326/abbf35|s2cid=229444533 }}</ref>

If reactors can be made to operate using only deuterium fuel, then the tritium replenishment issue is eliminated and neutron radiation damage may be reduced. However, the probabilities of deuterium-deuterium reactions are about 20 times lower than for deuterium-tritium. Additionally, the temperature needed is about 3 times higher than for deuterium-tritium (see [[#Cross section|cross section]]). The higher temperatures and lower reaction rates thus significantly complicate the engineering challenges.

== History ==
{{Main|History of nuclear fusion}}
{{cleanup rewrite|2=section|date=February 2023}}

=== Early experiments ===
[[File:Kink instability at Aldermaston.jpg|thumb|right|upright=1.5|Early photo of plasma inside a pinch machine (Imperial College 1950–1951)]]
[[File:A sun of our own newspaper headline.jpg|thumb|alt=The UK claimed that it had gotten fusion first in 1957 on ZETA, but this claim had to later be withdrawn. |The UK claimed that it had gotten fusion first in 1957 on ZETA, but this claim had to later be withdrawn.]]

The first machine to achieve controlled [[thermonuclear fusion]] was a [[Pinch (plasma physics)|pinch machine]] at Los Alamos National Laboratory called Scylla I at the start of 1958. The team that achieved it was led by a British scientist named [[James L. Tuck|James Tuck]] and included a young [[Marshall Rosenbluth]]. Tuck had been involved in the Manhattan project, but had switched to working on fusion in the early 1950s. He applied for funding for the project as part of a White House sponsored contest to develop a fusion reactor along with [[Lyman Spitzer]]. The previous year, 1957, the British had claimed that they had achieved thermonuclear fusion reactions on the [[ZETA (fusion reactor)|Zeta pinch machine]]. However, it turned out that the neutrons they had detected were from beam-target interactions, not fusion, and they withdrew the claim. A [[CERN]]-sponsored study group on controlled thermonuclear fusion met from 1958 to 1964. This group ceased when it became clear that CERN discontinued its limited support for plasma physics.<ref>{{Citation |last=Hof |first=Barbara |title=Fusion divided: what prevented European collaboration on controlled thermonuclear fusion in 1958 |date=2024-10-21 |url=https://arxiv.org/abs/2410.15969 |access-date=2025-02-14 |arxiv=2410.15969 }}</ref>

Scylla I was a classified machine at the time, so the achievement was hidden from the public. A traditional [[Z-pinch]] passes a current down the center of a plasma, which makes a magnetic force around the outside which squeezes the plasma to fusion conditions. Scylla I was a [[Theta pinch|θ-pinch]], which used deuterium to pass a current around the outside of its cylinder to create a magnetic force in the center.<ref name="Seife, Charles 2008" /><ref name="Phillips, James 2013" /> After the success of Scylla I, Los Alamos went on to build multiple pinch machines over the next few years.

Spitzer continued his stellarator research at Princeton. While fusion did not immediately transpire, the effort led to the creation of the [[Princeton Plasma Physics Laboratory]].<ref>{{Cite journal|last=Stix|first=T. H.|date=1998|title=Highlights in early stellarator research at Princeton|url=http://inis.iaea.org/Search/search.aspx?orig_q=RN:30002355|journal=Helical System Research|language=en}}</ref><ref>{{Cite tech report|last=Johnson|first=John L.|date=2001-11-16|title=The Evolution of Stellarator Theory at Princeton|url=https://www.osti.gov/biblio/792587-fxKdXU/native/|language=en|doi=10.2172/792587|osti=792587}}</ref>

=== First tokamak ===
In the early 1950s, Soviet physicists [[Igor Tamm|I.E. Tamm]] and [[Andrei Sakharov|A.D. Sakharov]] developed the concept of the tokamak, combining a low-power pinch device with a low-power stellarator.<ref name="quest" />
[[Andrei Sakharov|A.D. Sakharov]]'s group constructed the first tokamaks, achieving the first quasistationary fusion reaction.<ref>{{Cite book|last=Irvine|first=Maxwell |title=Nuclear power: a very short introduction|date=2014|publisher=Oxford University Press|isbn=978-0199584970|location=Oxford|language=en|oclc=920881367}}</ref><sup>:90</sup>

Over time, the "advanced tokamak" concept emerged, which included non-circular plasma, internal diverters and limiters, superconducting magnets, operation in the "H-mode" island of increased stability,<ref>{{Citation|last=Kusama|first=Y.|title=Requirements for Diagnostics in Controlling Advanced Tokamak Modes|date=2002|work=Advanced Diagnostics for Magnetic and Inertial Fusion|pages=31–38|editor-last=Stott|editor-first=Peter E.|place=Boston, MA|publisher=Springer US|language=en|doi=10.1007/978-1-4419-8696-2_5|isbn=978-1441986962|editor2-last=Wootton|editor2-first=Alan|editor3-last=Gorini|editor3-first=Giuseppe|editor4-last=Sindoni|editor4-first=Elio}}</ref> and the compact tokamak, with the magnets on the inside of the vacuum chamber.<ref>{{Cite journal|last=Menard|first=J. E.|date=2019-02-04|title=Compact steady-state tokamak performance dependence on magnet and core physics limits|url= |journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences|volume=377|issue=2141|pages=20170440|doi=10.1098/rsta.2017.0440|pmid=30967044|pmc=6365855|bibcode=2019RSPTA.37770440M|issn=1364-503X}}</ref><ref>{{Cite journal |last=Kaw |first=P. K. |date=1999 |title=Steady state operation of tokamaks |journal=Nuclear Fusion |volume=39 |issue=11 |pages=1605–1607 |doi=10.1088/0029-5515/39/11/411 |issn=0029-5515 |s2cid=250826481}}</ref>
[[File:TMX Baseball Coils.jpg|thumb|Magnetic mirrors suffered from end losses, requiring high power, complex magnetic designs, such as the baseball coil pictured here.]]
{{multiple image
| image1 = Novette laser.jpg
| width1 = 150
| caption1 = The Novette target chamber (metal sphere with diagnostic devices protruding radially), which was reused from the [[shiva laser|Shiva]] project and two newly built laser chains visible in background
| image2 = Fusion target implosion on NOVA laser.jpg
| width2 = 150
| caption2 = Inertial confinement fusion implosion on the [[Nova laser]] during the 1980s was a key driver of fusion development.
}}

=== First inertial confinement experiments ===
{{multiple image
 | total_width = 440
 | image1 = Shiva amplifier chains.jpg
 | caption1 = Shiva laser, 1977, the largest ICF laser system built in the seventies
 | image2 = The Tandem Mirror Experiment.jpg
 | caption2 = The Tandem Mirror Experiment (TMX) in 1979 }}

Laser fusion was suggested in 1962 by scientists at [[Lawrence Livermore National Laboratory]] (LLNL), shortly after the invention of the laser in 1960. [[Inertial confinement fusion]] experiments using lasers began as early as 1965.{{Citation needed|date=July 2024}} Several laser systems were built at LLNL, including the [[Argus laser|Argus]], the [[Cyclops laser|Cyclops]], the [[Janus laser|Janus]], the [[Long path laser|long path]], the [[Shiva laser]], and the [[Nova (laser)|Nova]].<ref>{{cite journal | doi = 10.1088/0029-5515/25/9/063 | volume=25 | title=Highlights of laser fusion related research by United Kingdom universities using the SERC Central Laser Facility at the Rutherford Appleton Laboratory | year=1985 | journal=Nuclear Fusion | pages=1351–1353 | last1 = Key | first1 = M.H.| issue=9 | s2cid=119922168 }}</ref>

Laser advances included frequency-tripling crystals that transformed infrared laser beams into ultraviolet beams and "chirping", which changed a single wavelength into a full spectrum that could be amplified and then reconstituted into one frequency.<ref>{{Cite book |title=Inertial confinement nuclear fusion : a historical approach by its pioneers|date=2007|publisher=Foxwell & Davies (UK)|editor=Verlarde, G. |editor2=Carpintero–Santamaría, Natividad |isbn=978-1905868100|location=London |oclc=153575814}}</ref> Laser research cost over one billion dollars in the 1980s.<ref name="NRDC">{{cite web |last1=McKinzie |first1=Matthew |last2=Paine |first2=Christopher E. |date=2000 |title=When peer review fails: The Roots of the National Ignition Facility (NIF) Debacle |url=http://www.nrdc.org/nuclear/nif2/findings.asp |access-date=30 October 2014 |publisher=National Resources Defense Council}}</ref>

=== 1980s ===
The [[Tore Supra]], [[Joint European Torus|JET]], [[T-15 (reactor)|T-15]], and [[JT-60]] tokamaks were built in the 1980s.<ref>{{cite web|url=http://www-drfc.cea.fr/gb/cea/ts/ts.htm |title=Tore Supra |access-date=February 3, 2016 |url-status=dead |archive-url=https://web.archive.org/web/20121115112229/http://www-drfc.cea.fr/gb/cea/ts/ts.htm |archive-date=November 15, 2012 }}</ref><ref>{{Cite journal |last=Smirnov |first=V. P. |date=2009-12-30 |title=Tokamak foundation in USSR/Russia 1950–1990 |url=http://fire.pppl.gov/nf_50th_5_Smirnov.pdf |journal=Nuclear Fusion |volume=50 |issue=1 |pages=014003 |doi=10.1088/0029-5515/50/1/014003 |issn=0029-5515 |s2cid=17487157}}</ref> In 1984, Martin Peng of ORNL proposed the [[spherical tokamak]] with a much smaller radius.<ref>Y-K Martin Peng, "Spherical Torus, Compact Fusion at Low Yield". Oak Ridge National Laboratory/FEDC-87/7 (December 1984)</ref> It used a single large conductor in the center, with magnets as half-rings off this conductor. The aspect ratio fell to as low as 1.2.<ref name="Small Tight">{{Cite journal|last=Sykes|first=Alan|date=1997|title=High β produced by neutral beam injection in the START (Small Tight Aspect Ratio Tokamak) spherical tokamak|journal=Physics of Plasmas|language=en|volume=4|issue=5|pages=1665–1671|doi=10.1063/1.872271|bibcode=1997PhPl....4.1665S|issn=1070-664X|doi-access=free}}</ref><sup>:B247</sup><ref>{{Cite book|last=Braams, C. M. |title=Nuclear fusion: half a century of magnetic confinement fusion research|author2=Stott, P. E. |year=2002|publisher=Institute of Physics Pub. |isbn=978-0367801519|oclc=1107880260}}</ref><sup>:225</sup> Peng's advocacy caught the interest of [[Derek Robinson (physicist)|Derek Robinson]], who built the [[Small Tight Aspect Ratio Tokamak]], (START).<ref name="Small Tight" />

=== 1990s ===
<!-- {{multiple image
 | width1 = 220
 | image1 = [[WP:NFCC]] violation: Z-machine480.jpg
 | caption1 = Z Machine (a pinch at SNL) went through a number of upgrades during the mid to late nineties }} -->

In 1991, the Preliminary Tritium Experiment at the [[Joint European Torus]] achieved the world's first controlled release of fusion power.<ref>{{Cite journal |last1=Jarvis |first1=O. N. |date=2006-06-16 |title=Neutron measurements from the preliminary tritium experiment at JET (invited) |journal=Review of Scientific Instruments |volume=63 |issue=10 |pages=4511–4516 |doi=10.1063/1.1143707}}</ref>

In 1996, Tore Supra created a plasma for two minutes with a current of almost 1&nbsp;million amperes, totaling 280 MJ of injected and extracted energy.<ref>{{Cite journal|last=Garin|first=Pascal|date=October 2001|title=Actively cooled plasma facing components in Tore Supra|url=http://dx.doi.org/10.1016/s0920-3796(01)00242-3|journal=Fusion Engineering and Design|volume=56–57|pages=117–123|doi=10.1016/s0920-3796(01)00242-3|bibcode=2001FusED..56..117G |issn=0920-3796}}</ref>

In 1997, JET produced a peak of 16.1&nbsp;MW of fusion power (65% of heat to plasma<ref>{{Cite book |author=European Commission Directorate-General for Research and Innovation |year=2004 |title=Fusion Research: An Energy Option for Europe's Future |location=Luxembourg |publisher=Office for Official Publications of the European Communities |isbn=92-894-7714-8 |oclc=450075815}}</ref>), with fusion power of over 10&nbsp;MW sustained for over 0.5&nbsp;sec.<ref>{{Cite book |last=Claessens |first=Michel|date=2020|title=ITER: The Giant Fusion Reactor|url=http://dx.doi.org/10.1007/978-3-030-27581-5|doi=10.1007/978-3-030-27581-5|isbn=978-3030275808|s2cid=243590344}}</ref>

=== 2000s ===
[[File:MAST plasma image.jpg|thumbnail|The [[Mega Ampere Spherical Tokamak]] became operational in the UK in 1999.]]

"Fast ignition"<ref>{{Cite book |last=Atzeni |first=Stefano |title=The physics of inertial fusion : beam plasma interaction, hydrodynamics, hot dense matter|date=2004|publisher=Clarendon Press|others=Meyer-ter-Vehn, Jürgen|isbn=978-0198562641|location=Oxford|oclc=56645784}}</ref><ref>{{Cite book|last=Pfalzner|first=Susanne|url=http://dx.doi.org/10.1201/9781420011845|title=An Introduction to Inertial Confinement Fusion|date=2006-03-02|publisher=CRC Press|doi=10.1201/9781420011845|isbn=978-0429148156}}</ref> saved power and moved ICF into the race for energy production.

In 2006, China's [[Experimental Advanced Superconducting Tokamak]] (EAST) test reactor was completed.<ref>{{Cite web|title=People's Daily Online – China to build world's first "artificial sun" experimental device|url=http://en.people.cn/200601/21/eng20060121_237208.html|access-date=2020-10-10|website=en.people.cn|archive-date=2011-06-05 |archive-url=https://web.archive.org/web/20110605190505/http://english.people.com.cn/200601/21/eng20060121_237208.html|url-status=dead}}</ref> It was the first tokamak to use superconducting magnets to generate both toroidal and poloidal fields.

In March 2009, the laser-driven ICF [[National Ignition Facility|NIF]] became operational.<ref>{{Cite web |title=What Is the National Ignition Facility? |url=https://lasers.llnl.gov/about/what-is-nif |access-date=2022-08-07 |website=lasers.llnl.gov |archive-url=https://web.archive.org/web/20170731064919/https://lasers.llnl.gov/about/what-is-nif |archive-date=July 31, 2017 |publisher=Lawrence Livermore National Laboratory}}</ref>

In the 2000s, privately backed fusion companies entered the race, including [[TAE Technologies]],<ref>{{Cite news|url=https://www.forbes.com/sites/michaelkanellos/2013/03/11/hollywood-silicon-valley-and-russia-join-forces-on-nuclear-fusion/#12c2795972ba|title=Hollywood, Silicon Valley and Russia Join Forces on Nuclear Fusion|last=Kanellos|first=Michael|work=Forbes|access-date=2017-08-21|language=en}}</ref> [[General Fusion]],<ref>{{Cite web|last=Frochtzwajg|first=Jonathan|title=The secretive, billionaire-backed plans to harness fusion|url=http://www.bbc.com/future/story/20160428-the-secretive-billionaire-backed-plans-to-harness-fusion|access-date=2017-08-21|website=BBC|date=April 28, 2016 }}</ref><ref>{{Cite journal|last=Clery|first=Daniel|date=2014-07-25|title=Fusion's restless pioneers|journal=Science|language=en|volume=345|issue=6195|pages=370–375|bibcode=2014Sci...345..370C|doi=10.1126/science.345.6195.370|issn=0036-8075|pmid=25061186|ref=none}}</ref> and [[Tokamak Energy]].<ref>{{Cite web |last=Gray |first=Richard |date=19 April 2017 |title=The British reality TV star building a fusion reactor |url=http://www.bbc.com/future/story/20170418-the-made-in-chelsea-star-building-a-fusion-reactor |access-date=2017-08-21 |website=BBC}}</ref>

=== 2010s ===
[[File:Preamplifier at the National Ignition Facility.jpg|upright=1.15|thumb|The preamplifiers of the National Ignition Facility. In 2012, the NIF achieved a 500-terawatt shot.]]
[[File:Wendelstein7-X Torushall-2011.jpg|upright=1.15|thumb|The Wendelstein7X under construction]]
[[File:W7X-Spulen Plasma blau gelb.jpg|thumb|upright=1.15|Example of a stellarator design: A coil system (blue) surrounds plasma (yellow). A magnetic field line is highlighted in green on the yellow plasma surface.]]

Private and public research accelerated in the 2010s. General Fusion developed plasma injector technology and Tri Alpha Energy tested its C-2U device.<ref>{{Cite journal|last=Clery|first=Daniel|date=2017-04-28|title=Private fusion machines aim to beat massive global effort|journal=Science|language=en|volume=356|issue=6336|pages=360–361|bibcode=2017Sci...356..360C|doi=10.1126/science.356.6336.360|issn=0036-8075|pmid=28450588|s2cid=206621512}}</ref> The French [[Laser Mégajoule]] began operation. NIF achieved net energy gain<ref>{{cite web |title=PW 2012: fusion laser on track for 2012 burn |publisher=Optics.org |author=SPIE Europe Ltd |url=http://optics.org/news/3/1/37 |access-date=2013-06-22}}</ref> in 2013, as defined in the very limited sense as the hot spot at the core of the collapsed target, rather than the whole target.<ref>{{cite news |url=https://www.bbc.co.uk/news/science-environment-24429621 |title=Nuclear fusion milestone passed at US lab |publisher=BBC News |access-date=30 October 2014}}</ref>

In 2014, [[Phoenix Nuclear Labs]] sold a high-yield [[neutron generator]] that could sustain 5×10<sup>11</sup> [[deuterium]] fusion reactions per second over a 24-hour period.<ref>{{cite web|url=http://phoenixnuclearlabs.com/product/high-yield-neutron-generator/|title=The Alectryon High Yield Neutron Generator|year=2013|publisher=Phoenix Nuclear Labs}}</ref>

In 2015, [[MIT]] announced a [[tokamak]] it named the [[ARC fusion reactor]], using [[rare-earth barium-copper oxide]] (REBCO) superconducting tapes to produce high-magnetic field coils that it claimed could produce comparable magnetic field strength in a smaller configuration than other designs.<ref>{{cite news |last=Chandler |first=David L. |title=A small, modular, efficient fusion plant |work=MIT News |publisher=MIT News Office |url=http://newsoffice.mit.edu/2015/small-modular-efficient-fusion-plant-0810 |date=10 August 2015}}</ref>

In October, researchers at the [[Max Planck Institute of Plasma Physics]] in Greifswald, Germany, completed building the largest [[stellarator]] to date, the [[Wendelstein 7-X]] (W7-X). The W7-X stellarator began Operational phase 1 (OP1.1) on 10 December 2015, successfully producing helium plasma.<ref>{{Cite journal|url=https://iopscience.iop.org/article/10.1088/0029-5515/55/12/126001|title=Plans for the first plasma operation of Wendelstein 7-X|journal=Nuclear Fusion |date=November 2015 |volume=55 |issue=12 |page=126001 |doi=10.1088/0029-5515/55/12/126001 |last1=Sunn Pedersen |first1=T. |last2=Andreeva |first2=T. |last3=Bosch |first3=H. -S |last4=Bozhenkov |first4=S. |last5=Effenberg |first5=F. |last6=Endler |first6=M. |last7=Feng |first7=Y. |last8=Gates |first8=D. A. |last9=Geiger |first9=J. |last10=Hartmann |first10=D. |last11=Hölbe |first11=H. |last12=Jakubowski |first12=M. |last13=König |first13=R. |last14=Laqua |first14=H. P. |last15=Lazerson |first15=S. |last16=Otte |first16=M. |last17=Preynas |first17=M. |last18=Schmitz |first18=O. |last19=Stange |first19=T. |last20=Turkin |first20=Y. |bibcode=2015NucFu..55l6001P |hdl=11858/00-001M-0000-0029-04EB-D |s2cid=67798335 |hdl-access=free }}</ref> The objective was to test vital systems and understand the machine's physics. By February 2016, hydrogen plasma was achieved, with temperatures reaching up to 100 million Kelvin. The initial tests used five graphite limiters. After over 2,000 pulses and achieving significant milestones, OP1.1 concluded on 10 March 2016. An upgrade followed, and OP1.2 in 2017 aimed to test an uncooled divertor. By June 2018, record temperatures were reached. W7-X concluded its first campaigns with limiter and island divertor tests, achieving notable advancements by the end of 2018.<ref>{{cite journal |title=Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000 |journal=Nature Communications |volume=7 |pages=13493 |doi=10.1038/ncomms13493|pmid=27901043 |pmc=5141350 |year=2016 |last1=Pedersen |first1=T. Sunn |last2=Otte |first2=M. |last3=Lazerson |first3=S. |last4=Helander |first4=P. |last5=Bozhenkov |first5=S. |last6=Biedermann |first6=C. |last7=Klinger |first7=T. |last8=Wolf |first8=R. C. |last9=Bosch |first9=H. -S. |last10=Abramovic |first10=Ivana |last11=Äkäslompolo |first11=Simppa |last12=Aleynikov |first12=Pavel |last13=Aleynikova |first13=Ksenia |last14=Ali |first14=Adnan |last15=Alonso |first15=Arturo |last16=Anda |first16=Gabor |last17=Andreeva |first17=Tamara |last18=Ascasibar |first18=Enrique |last19=Baldzuhn |first19=Jürgen |last20=Banduch |first20=Martin |last21=Barbui |first21=Tullio |last22=Beidler |first22=Craig |last23=Benndorf |first23=Andree |last24=Beurskens |first24=Marc |last25=Biel |first25=Wolfgang |last26=Birus |first26=Dietrich |last27=Blackwell |first27=Boyd |last28=Blanco |first28=Emilio |last29=Blatzheim |first29=Marko |last30=Bluhm |first30=Torsten |display-authors=29 |bibcode=2016NatCo...713493P }}</ref><ref>{{Cite journal|title=Performance of Wendelstein 7-X stellarator plasmas during the first divertor operation phase|first1=R. C.|last1=Wolf|first2=A.|last2=Alonso|first3=S.|last3=Äkäslompolo|first4=J.|last4=Baldzuhn|first5=M.|last5=Beurskens|first6=C. D.|last6=Beidler|first7=C.|last7=Biedermann|first8=H.-S.|last8=Bosch|first9=S.|last9=Bozhenkov|first10=R.|last10=Brakel|first11=H.|last11=Braune|first12=S.|last12=Brezinsek|first13=K.-J.|last13=Brunner|first14=H.|last14=Damm|first15=A.|last15=Dinklage|first16=P.|last16=Drewelow|first17=F.|last17=Effenberg|first18=Y.|last18=Feng|first19=O.|last19=Ford|first20=G.|last20=Fuchert|first21=Y.|last21=Gao|first22=J.|last22=Geiger|first23=O.|last23=Grulke|first24=N.|last24=Harder|first25=D.|last25=Hartmann|first26=P.|last26=Helander|first27=B.|last27=Heinemann|first28=M.|last28=Hirsch|first29=U.|last29=Höfel|first30=C.|last30=Hopf|first31=K.|last31=Ida|first32=M.|last32=Isobe|first33=M. W.|last33=Jakubowski|first34=Y. O.|last34=Kazakov|first35=C.|last35=Killer|first36=T.|last36=Klinger|first37=J.|last37=Knauer|first38=R.|last38=König|first39=M.|last39=Krychowiak|first40=A.|last40=Langenberg|first41=H. P.|last41=Laqua|first42=S.|last42=Lazerson|first43=P.|last43=McNeely|first44=S.|last44=Marsen|first45=N.|last45=Marushchenko|first46=R.|last46=Nocentini|first47=K.|last47=Ogawa|first48=G.|last48=Orozco|first49=M.|last49=Osakabe|first50=M.|last50=Otte|first51=N.|last51=Pablant|first52=E.|last52=Pasch|first53=A.|last53=Pavone|first54=M.|last54=Porkolab|first55=A.|last55=Puig Sitjes|first56=K.|last56=Rahbarnia|first57=R.|last57=Riedl|first58=N.|last58=Rust|first59=E.|last59=Scott|first60=J.|last60=Schilling|first61=R.|last61=Schroeder|first62=T.|last62=Stange|first63=A.|last63=von Stechow|first64=E.|last64=Strumberger|first65=T.|last65=Sunn Pedersen|first66=J.|last66=Svensson|first67=H.|last67=Thomson|first68=Y.|last68=Turkin|first69=L.|last69=Vano|first70=T.|last70=Wauters|first71=G.|last71=Wurden|first72=M.|last72=Yoshinuma|first73=M.|last73=Zanini|first74=D.|last74=Zhang|date=1 August 2019|journal=Physics of Plasmas|volume=26|issue=8|pages=082504|doi=10.1063/1.5098761|bibcode=2019PhPl...26h2504W |s2cid=202127809 |doi-access=free|hdl=1721.1/130063|hdl-access=free}}</ref><ref>{{Cite journal|title=Experimental confirmation of efficient island divertor operation and successful neoclassical transport optimization in Wendelstein 7-X|journal=Nuclear Fusion |date=April 2022 |volume=62 |issue=4 |page=042022 |doi=10.1088/1741-4326/ac2cf5 |last1=Sunn Pedersen |first1=Thomas |last2=Abramovic |first2=I. |last3=Agostinetti |first3=P. |last4=Agredano Torres |first4=M. |last5=Äkäslompolo |first5=S. |last6=Alcuson Belloso |first6=J. |last7=Aleynikov |first7=P. |last8=Aleynikova |first8=K. |last9=Alhashimi |first9=M. |last10=Ali |first10=A. |last11=Allen |first11=N. |last12=Alonso |first12=A. |last13=Anda |first13=G. |last14=Andreeva |first14=T. |last15=Angioni |first15=C. |last16=Arkhipov |first16=A. |last17=Arnold |first17=A. |last18=Asad |first18=W. |last19=Ascasibar |first19=E. |last20=Aumeunier |first20=M. -H |last21=Avramidis |first21=K. |last22=Aymerich |first22=E. |last23=Baek |first23=S. -G |last24=Bähner |first24=J. |last25=Baillod |first25=A. |last26=Balden |first26=M. |last27=Balden |first27=M. |last28=Baldzuhn |first28=J. |last29=Ballinger |first29=S. |last30=Banduch |first30=M. |bibcode=2022NucFu..62d2022S |s2cid=234338848 |display-authors=1 |doi-access=free |hdl=1721.1/147631 |hdl-access=free }}</ref> It soon produced helium and hydrogen plasmas lasting up to 30 minutes.<ref>{{Cite web|last=Max Planck Institute for Experimental Physics|date=February 3, 2016|title=Wendelstein 7-X fusion device produces its first hydrogen plasma|url=https://www.ipp.mpg.de/4010154/02_16|access-date=2021-06-15|website=www.ipp.mpg.de|language=en}}</ref>

In 2017, [[Helion Energy]]'s fifth-generation plasma machine went into operation.<ref>{{Cite web|last=Wang|first=Brian|date=August 1, 2018|title=Nuclear Fusion Updated project reviews|url=https://www.nextbigfuture.com/2018/08/nuclear-fusion-updated-project-reviews.html|access-date=2018-08-03|website=www.nextbigfuture.com|language=en-US}}</ref> The UK's Tokamak Energy's [[Tokamak Energy|ST40]] generated "first plasma".<ref>{{Cite web|url=https://www.sciencealert.com/the-uk-has-just-switch-on-its-tokamak-nuclear-fusion-reactor|title=The UK Just Switched on an Ambitious Fusion Reactor – And It Works|last=MacDonald|first=Fiona|website=ScienceAlert|date=May 2017 |language=en-gb|access-date=2019-07-03}}</ref> The next year, [[Eni]] announced a $50&nbsp;million investment in [[Commonwealth Fusion Systems]], to attempt to commercialize MIT's [[ARC fusion reactor|ARC]] technology.<ref>{{cite news |url=https://www.reuters.com/article/us-nuclearpower-fusion-eni/italys-eni-defies-skeptics-may-up-stake-in-nuclear-fusion-project-idUSKBN1HK1JJ |title=Italy's Eni defies sceptics, may up stake in nuclear fusion project |date=13 April 2018|newspaper=Reuters }}</ref><ref>{{cite web |url=https://www.seeker.com/energy/mit-aims-to-harness-fusion-power-within-15-years |title=MIT Aims to Harness Fusion Power Within 15 years |date=3 April 2018}}</ref><ref>{{cite web| url=http://www.wbur.org/bostonomix/2018/03/09/mit-nuclear-fusion |title=MIT Aims To Bring Nuclear Fusion To The Market In 10 Years |date=9 March 2018}}</ref><ref>{{cite web |last=Chandler |first=David |date=9 March 2018 |title=MIT and newly formed company launch novel approach to fusion power |url=https://news.mit.edu/2018/mit-newly-formed-company-launch-novel-approach-fusion-power-0309 |website=MIT News |publisher=Massachusetts Institute of Technology}}</ref>

=== 2020s ===
In January 2021, SuperOx announced the commercialization of a new [[superconducting wire]] with more than 700 A/mm<sup>2</sup> current capability.<ref>{{cite journal |last1=Molodyk |first1=A. |last2=Samoilenkov |first2=S. |last3=Markelov |first3=A. |last4=Degtyarenko |first4=P. |last5=Lee |first5=S. |last6=Petrykin |first6=V. |last7=Gaifullin |first7=M. |last8=Mankevich |first8=A. |last9=Vavilov |first9=A. |last10=Sorbom |first10=B. |last11=Cheng |first11=J. |last12=Garberg |first12=S. |last13=Kesler |first13=L. |last14=Hartwig |first14=Z. |last15=Gavrilkin |first15=S. |last16=Tsvetkov |first16=A. |last17=Okada |first17=T. |last18=Awaji |first18=S. |last19=Abraimov |first19=D. |last20=Francis |first20=A. |last21=Bradford |first21=G. |last22=Larbalestier |first22=D. |last23=Senatore |first23=C. |last24=Bonura |first24=M. |last25=Pantoja |first25=A. E. |last26=Wimbush |first26=S. C. |last27=Strickland |first27=N. M. |last28=Vasiliev |first28=A. |title=Development and large volume production of extremely high current density YBa 2 Cu 3 O 7 superconducting wires for fusion |journal=Scientific Reports |date=22 January 2021 |volume=11 |issue=1 |pages=2084 |doi=10.1038/s41598-021-81559-z|pmid=33483553 |pmc=7822827 }}</ref>

TAE Technologies announced results for its Norman device, holding a temperature of about 60&nbsp;MK for 30 milliseconds, 8 and 10 times higher, respectively, than the company's previous devices.<ref>{{Cite web|last=Clery|first=Daniel|date=2021-04-08|title=With "smoke ring" technology, fusion startup marks steady progress|url=https://www.science.org/content/article/smoke-ring-technology-fusion-startup-marks-steady-progress|access-date=2021-04-11|website=Science {{!}} AAAS|language=en}}</ref>

In October, Oxford-based [[First Light Fusion]] revealed its projectile fusion project, which fires an aluminum disc at a fusion target, accelerated by a 9 mega-amp electrical pulse, reaching speeds of {{Convert|20|km/s}}. The resulting fusion generates neutrons whose energy is captured as heat.<ref>{{Cite news|last=Morris|first=Ben|date=2021-09-30|title=Clean energy from the fastest moving objects on earth|language=en-GB |publisher=BBC News |url=https://www.bbc.com/news/business-58602159|access-date=2021-12-09}}</ref>

On November 8, in an invited talk to the 63rd Annual Meeting of the APS Division of Plasma Physics,<ref>{{Cite conference |conference=63rd Annual Meeting of the APS Division of Plasma Physics, November 8–12, 2021; Pittsburgh, PA |url=https://meetings.aps.org/Meeting/DPP21/Session/AR01?showAbstract|title = Session AR01: Review: Creating A Burning Plasma on the National Ignition Facility|volume = 66|issue = 13 |work= Bulletin of the American Physical Society}}</ref> the National Ignition Facility claimed<ref name="physics_v14_168">{{Cite journal 
|url=https://physics.aps.org/articles/v14/168|title = Ignition First in a Fusion Reaction|journal = Physics|date = November 30, 2021|volume = 14|last1 = Wright|first1 = Katherine|page = 168|doi = 10.1103/Physics.14.168|bibcode = 2021PhyOJ..14..168W|s2cid = 244829710|doi-access = free}}</ref> to have triggered [[fusion ignition]] in the laboratory on August 8, 2021, for the first time in the 60+ year history of the ICF program.<ref>{{Cite web |last=Dunning |first=Hayley |date=17 August 2021 |title=Major nuclear fusion milestone reached as "ignition" triggered in a lab |url=https://phys.org/news/2021-08-major-nuclear-fusion-milestone-ignition.html |website=Science X Network}}</ref><ref>{{Cite web |last=Bishop |first=Breanna |date=18 August 2021 |title=National Ignition Facility experiment puts researchers at threshold of fusion ignition |url=https://www.llnl.gov/news/national-ignition-facility-experiment-puts-researchers-threshold-fusion-ignition |website=Lawrence Livermore National Laboratory}}</ref> The shot yielded 1.3 MJ of fusion energy, an over 8X improvement on tests done in spring of 2021.<ref name="physics_v14_168" /> NIF estimates that 230&nbsp;kJ of energy reached the fuel capsule, which resulted in an almost 6-fold energy output from the capsule.<ref name="physics_v14_168" /> A researcher from Imperial College London stated that the majority of the field agreed that ignition had been demonstrated.<ref name="physics_v14_168" />

In November 2021, [[Helion Energy]] reported receiving $500 million in Series E funding for its seventh-generation Polaris device, designed to demonstrate net electricity production, with an additional $1.7&nbsp;billion of commitments tied to specific milestones,<ref>{{Cite web|last=Conca|first=James|title=Helion Energy Raises $500 Million On The Fusion Power Of Stars|url=https://www.forbes.com/sites/jamesconca/2021/11/09/helion-energy-raises-500-million-on-the-fusion-power-of-stars/|access-date=2021-12-19|website=Forbes|language=en}}</ref> while Commonwealth Fusion Systems raised an additional $1.8&nbsp;billion in Series B funding to construct and operate its [[SPARC (tokamak)|SPARC tokamak]], the single largest investment in any private fusion company.<ref>{{Cite news|last=Journal|first=Jennifer Hiller {{!}} Photographs by Tony Luong for The Wall Street|date=2021-12-01|title=WSJ News Exclusive {{!}} Nuclear-Fusion Startup Lands $1.8 Billion as Investors Chase Star Power|language=en-US|work=Wall Street Journal|url=https://www.wsj.com/articles/nuclear-fusion-startup-lands-1-8-billion-as-investors-chase-star-power-11638334801|access-date=2021-12-17|issn=0099-9660}}</ref>

In April 2022, First Light announced that their hypersonic projectile fusion prototype had produced neutrons compatible with fusion. Their technique electromagnetically fires projectiles at [[Mach number|Mach]] 19 at a caged fuel pellet. The deuterium fuel is compressed at Mach 204, reaching pressure levels of 100 TPa.<ref>{{Cite web |last=Blain |first=Loz |date=2022-04-06 |title=Oxford spinoff demonstrates world-first hypersonic "projectile fusion" |url=https://newatlas.com/energy/first-light-nuclear-fusion-projectile/ |access-date=2022-04-06 |website=New Atlas |language=en-US}}</ref>

On December 13, 2022, the [[US Department of Energy]] reported that researchers at the National Ignition Facility had achieved a net energy gain from a fusion reaction. The reaction of hydrogen fuel at the facility produced about 3.15 MJ of energy while consuming 2.05 MJ of input. However, while the fusion reactions may have produced more than 3 megajoules of energy—more than was delivered to the target—NIF's 192 lasers consumed 322 MJ of grid energy in the conversion process.<ref name="NYT-209221213"/><ref name="Ignition" /><ref name="WP-20221212">{{cite news |last=Osaka |first=Shannon |title=What you need to know about the U.S. fusion energy breakthrough |url=https://www.washingtonpost.com/climate-solutions/2022/12/12/nuclear-fusion-breakthrough-benefits/ |date=12 December 2022 |newspaper=[[The Washington Post]] |access-date=13 December 2022 }}</ref><ref>{{Cite web |last=Hartsfield |first=Tom |date=December 13, 2022 |title=There is no "breakthrough": NIF fusion power still consumes 130 times more energy than it creates |url=https://bigthink.com/the-future/fusion-power-nif-hype-lose-energy/ |website=Big Think}}</ref>

In May 2023, the [[United States Department of Energy]] (DOE) provided a grant of $46 million to eight companies across seven states to support fusion power plant design and research efforts. This funding, under the Milestone-Based Fusion Development Program, aligns with objectives to demonstrate pilot-scale fusion within a decade and to develop fusion as a carbon-neutral energy source by 2050. The granted companies are tasked with addressing the scientific and technical challenges to create viable fusion pilot plant designs in the next 5–10 years. The recipient firms include [[Commonwealth Fusion Systems]], Focused Energy Inc., Princeton Stellarators Inc., Realta Fusion Inc., Tokamak Energy Inc., Type One Energy Group, Xcimer Energy Inc., and Zap Energy Inc.<ref>{{Cite news |last=Gardner |first=Timothy |date=1 June 2023 |title=US announces $46 million in funds to eight nuclear fusion companies |agency=Reuters}}</ref> 

In December 2023, the largest and most advanced tokamak JT-60SA was inaugurated in [[Naka, Ibaraki|Naka]], Japan. The reactor is a joint project between Japan and the European Union. The reactor had achieved its first plasma in October 2023.<ref>{{cite web |last=Dobberstein |first=Laura |date=4 December 2023 |title=World's largest nuclear fusion reactor comes online in Japan |url=https://www.theregister.com/2023/12/04/jt_60sa_tokamak_online/ |website=The Register |publisher=Situation Publishing}}</ref> Subsequently, South Korea's fusion reactor project, the [[Korean Superconducting Tokamak Advanced Research]], successfully operated for 102 seconds in a high-containment mode (H-mode) containing high ion temperatures of more than 100 million degrees in plasma tests conducted from December 2023 to February 2024.<ref>{{Cite news |date=March 21, 2024 |title=S. Korea's artificial sun project KSTAR achieves longest operation time of 102 seconds |url=https://m.ajudaily.com/view/20240321111705997 |work=[[Aju Business Daily]]}}</ref>

In January 2025, EAST fusion reactor in China was reported to maintain a steady-state high-confinement plasma operation for 1066 seconds.<ref>{{Cite web|url=https://english.news.cn/20250120/1d4e392ccaef48f29e8e9cdd0f9360c5/c.html|title=China Focus: Chinese "artificial sun" sets new record in milestone step toward fusion power generation|website=english.news.cn}}</ref> In February 2025, the French Alternative Energies and Atomic Energy Commission (CEA) announced that its [[WEST (formerly Tore Supra)|WEST]] tokamak had maintained a stable plasma for 1,337 seconds—over 22 minutes. <ref name=":0">{{Cite web |last=CEA |date=2025-02-18 |title=Nuclear fusion: WEST beats the world record for plasma duration! |url=https://www.cea.fr/english/Pages/News/nuclear-fusion-west-beats-the-world-record-for-plasma-duration.aspx |access-date=2025-02-20 |website=CEA/English Portal |language=en}}</ref>

==Future development==
Claims of commercially viable fusion power being relatively imminent have often attracted ridicule within the scientific community.<ref>[https://link.springer.com/article/10.1007/s10894-023-00361-z#:~:text=To%20be%20precise%2C%20we%20should,is%20only%2017.8%20years%20away. How Many Years Away is Fusion Energy? A Review]. ''Journal of Fusion Energy''. 12 May 2023. Retrieved 29 December 2024.</ref> A common joke is that human-engineered fusion has always been promised as 30 years away since the concept was first discussed,<ref>[https://www.theguardian.com/science/article/2024/aug/11/nuclear-fusion-research-tae-power-solutions-cancer-propulsion Fusion power might be 30 years away but we will reap its benefits well before]. ''The Guardian''. 11 August 2024. Retrieved 29 December 2024.</ref> or that it has been "20 years away for 50 years".<ref>[https://www.space.com/when-will-we-achieve-fusion-power We've been 'close' to achieving fusion power for 50 years. When will it actually happen?]. ''Space.com''. 14 January 2024. Retrieved 29 December 2024.</ref>

In 2024, [[Commonwealth Fusion Systems]] announced plans to build the world's first grid-scale commercial nuclear fusion power plant at the James River Industrial Center in [[Chesterfield County, Virginia]], which is part of the [[Greater Richmond Region]]; the plant is designed to produce about 400 MW of electric power, and is intended to come online in the early 2030s.<ref>{{Cite web |date=2024-12-18 |title=World's first commercial fusion power plant coming to Chesterfield |url=https://rictoday.6amcity.com/business/cfs-worlds-first-fusion-power-plant-richmond-va |access-date=2024-12-19 |website=6AM - RICtoday |language=en}}</ref><ref>{{cite news|title=Virginia to host world's first fusion power plant|newspaper=Virginia Mercury|date=December 18, 2024|url=https://virginiamercury.com/2024/12/18/virginia-to-host-worlds-first-fusion-power-plant/}}</ref><ref>{{Cite web|url=https://news.mit.edu/2024/commonwealth-fusion-systems-unveils-worlds-first-fusion-power-plant-1217|title=MIT spinout Commonwealth Fusion Systems unveils plans for the world's first fusion power plant|date=December 17, 2024|website=Massachusetts Institute of Technology News}}</ref>

== Records ==
Fusion records continue to advance:

{| class="wikitable sortable"
|+Records
! Domain !! Year !! Record !! Device !! Notes
|-
| Plasma temperature|| 2012 || 1.8{{e|9}} K || Focus-Fusion 1<ref>{{cite journal |last1=Lerner |first1=Eric J. |last2=Murali |first2=S. Krupakar |last3=Shannon |first3=Derek |last4=Blake |first4=Aaron M. |last5=Van Roessel |first5=Fred |date=23 March 2012 |title=Fusion reactions from >150 keV ions in a dense plasma focus plasmoid |journal=Physics of Plasmas |volume=19 |issue=3 |pages=032704 |bibcode=2012PhPl...19c2704L |doi=10.1063/1.3694746 |s2cid=120207711}}</ref><ref>{{cite news|last=Halper|first=Mark|title=Fusion breakthrough|url=http://www.smartplanet.com/blog/intelligent-energy/fusion-breakthrough/14516|access-date=1 April 2012|newspaper=Smart PLanet|date=March 28, 2012}}</ref> ||
|-
| Fusion power || 1997 || 1.6{{e|7}} W || [[Joint European Torus|JET]]<ref name="ccfe">{{cite web|title=JET|url=http://www.ccfe.ac.uk/jet.aspx|url-status=dead|archive-url=https://web.archive.org/web/20160707193828/http://www.ccfe.ac.uk/jet.aspx|archive-date=July 7, 2016|access-date=26 June 2016|publisher=Culham Centre Fusion Energy}}</ref> ||
|-
|Tokamak fusion energy
|2023
|6.9{{e|7}} J
|JET<ref>{{Cite web |last=Tischler |first=Karl |date=2024-02-08 |title=Breaking New Ground: JET Tokamak's Latest Fusion Energy Record Shows Mastery of Fusion Processes |url=https://euro-fusion.org/eurofusion-news/dte3record/ |access-date=2024-02-11 |website=EUROfusion |language=en-US}}</ref>
|
|-
| ICF fusion energy || 2022 || 3.15{{e|6}} J || [[National Ignition Facility|NIF]]<ref name="WP-20221212"/> ||Delivering 2.05 megajoules (MJ) of light energy to the target, resulting in 3.15 MJ of fusion energy output from appr. 400 MJ electric energy to drive the lasers.
|-
| ICF shot rate || 2013 || Over 90K shots over 10 hours; Over 11 million pulse power shots at 10 Hz for over 12 days; || Electra laser at the [[Naval Research Laboratory]]<ref>{{cite journal|author=Obenschain, Stephen | display-authors=etal|title=High-energy krypton fluoride lasers for inertial fusion|journal=Applied Optics|volume=54|issue=31|year=2015|pages=F103–F122|doi=10.1364/AO.54.00F103| pmid=26560597| bibcode=2015ApOpt..54F.103O}}</ref> <ref>"Krypton Fluoride (KrF) Laser Driver for Inertial Fusion Energy"</ref> ||
|-
| Plasma pressure || 2016 || 2.1{{e|5}} Pa || [[Alcator C-Mod]]<ref>{{Cite web|title=New record for fusion|url=https://news.mit.edu/2016/alcator-c-mod-tokamak-nuclear-fusion-world-record-1014|access-date=2020-10-11|website=MIT News {{!}} Massachusetts Institute of Technology|date=October 14, 2016 |language=en}}</ref> ||
|-
| [[Lawson criterion]] || 2013 || 1.53{{e|24}} eV·s/m<sup>3</sup> || [[JT-60]]<ref>{{cite web |url=http://www-jt60.naka.jaea.go.jp/english/html/exp_rep/rep36.html |title=World Highest Fusion Triple Product Marked in High-βp H-mode Plasmas |archive-url=https://web.archive.org/web/20130106002319/http://www-jt60.naka.jaea.go.jp/english/html/exp_rep/rep36.html |archive-date=2013-01-06 }}</ref><ref>{{Cite web|title=Measuring Progress in Fusion Energy: The Triple Product|url=https://www.fusionenergybase.com/article/measuring-progress-in-fusion-energy-the-triple-product/|access-date=2020-10-10|website=www.fusionenergybase.com|language=en|archive-date=2020-10-01 |archive-url=https://web.archive.org/web/20201001051629/https://www.fusionenergybase.com/article/measuring-progress-in-fusion-energy-the-triple-product/|url-status=dead}}</ref> ||
|-
| [[Fusion energy gain factor]] || 2022 || 1.54 || NIF<ref name="WP-20221212"/> ||
|-
| Discharge time (field reversed configuration) || 2016 || 3{{e|-1}} s || [[Princeton field-reversed configuration|Princeton Field Reversed Configuration]]<ref>Cohen, Sam, and B. Berlinger. "Long-pulse Operation of the PFRC-2 Device." The Joint US-Japan Compact Torus. Wisconsin, Madison. 22 Aug. 2016. Lecture.</ref> ||Fusion was not observed. Discharge time is not confinement time.
|-
| Discharge time (stellarator) || 2019 || >1{{e|2}} s || [[Wendelstein 7-X]]<ref>{{Cite web|url=https://www.ipp.mpg.de/4550215/11_18|title=Successful second round of experiments with Wendelstein 7-X|website=www.ipp.mpg.de|language=en|access-date=22 March 2019}}</ref><ref>{{Cite web|url=https://newatlas.com/wendelstein-7-x-nuclear-fusion-records/57394|title=Wendelstein 7-X fusion reactor keeps its cool en route to record-breaking results|last=Lavars|first=Nick|date=26 November 2018|website=newatlas.com|language=en|access-date=1 December 2018}}</ref> ||
|-
|Discharge time (tokamak)
|2022
|>1{{e|3}} s
|EAST<ref>{{Cite web|url=https://www.smithsonianmag.com/smart-news/chinas-artificial-sun-reactor-broke-record-for-nuclear-fusion-180979336/|title=China's Artificial Sun Just Broke a Record for Longest Sustained Nuclear Fusion|first1=Smithsonian|last1=Magazine|first2=Elizabeth|last2=Gamillo|website=Smithsonian Magazine}}</ref>
|
|-
|Discharge time x temperature (tokamak)
|2021
|1.2{{e|10}} K·s
|EAST<ref>{{Cite web|title=China's "Artificial Sun" Fusion Reactor Just Set a World Record|url=https://futurism.com/chinas-artificial-sun-fusion-reactor-just-set-a-world-record|website=Futurism|date=June 2, 2021 }}</ref>
|
|-
| [[Plasma beta|Beta]] || 1998 || 0.4 || [[Small Tight Aspect Ratio Tokamak]]<ref>Alan Sykes, [http://www.triam.kyushu-u.ac.jp/ICPP/program/download/12-PL01.pdf "The Development of the Spherical Tokamak"] {{webarchive |url=https://web.archive.org/web/20110722072454/http://www.triam.kyushu-u.ac.jp/ICPP/program/download/12-PL01.pdf |date=July 22, 2011 }}, ICPP, Fukuoka September 2008</ref> ||
|-
|Temperature (compact spherical tokamak)
|2022
|1{{e|8}} K
|[[Tokamak Energy]]<ref>{{Cite web |last=Szondy |first=David |date=2022-03-13 |title=Tokamak Energy achieves temperature threshold for commercial fusion |url=https://newatlas.com/energy/tokamak-energy-temperature-threshold-commercial-fusion/ |access-date=2022-03-15 |website=New Atlas |language=en-US}}</ref>
|
|-
|Temperature x time (tokamak)
|2021
|3{{e|9}} K·s
|[[KSTAR]]<ref>{{Cite web |last=Lavars |first=Nick |date=2021-11-24 |title=KSTAR fusion reactor sets record with 30-second plasma confinement |url=https://newatlas.com/energy/kstar-fusion-reactor-record-30-second-plasma/ |access-date=2022-03-15 |website=New Atlas |language=en-US}}</ref>
|
|-
|Stable plasma (tokamak)
|2025
|1,337 seconds
|[[WEST (formerly Tore Supra)|WEST]]<ref name=":0" />
|
|}
<!--
Fusion power trends as the plasma confinement raised to the fourth power.<ref>"Fusion energy and why it is important to chase the impossible" Dr. Melanie Windridge, TED x Warwick, April 19th 2018.</ref> Hence, getting a strong plasma trap is of real value to a fusion power plant.  Plasma has a very good [[electrical conductivity]]. This opens the possibility of confining the plasma with [[magnetic field]], generally known as [[magnetic confinement fusion|magnetic confinement]]. The field puts a magnetic pressure on the plasma, which holds it in.  A widely used measure of magnetic trapping in fusion is the beta ratio (plasma pressure/magnetic field pressure):

<math>\beta = \frac{p}{p_{mag}} = \frac{n k_B T}{(B^2/2\mu_0)}</math><ref>{{Cite book|last=Wesson, John |title=Tokamaks|date=2004|publisher=Clarendon Press|others=Campbell, D. J.|isbn=0198509227|edition=3rd|location=Oxford|oclc=52324306}}</ref>{{rp|115}}

This is the ratio of the externally applied field to the internal pressure of the plasma. A value of 1 is ideal trapping. Some examples of beta values include:

# The [[Small Tight Aspect Ratio Tokamak|START]] machine: 0.32
# The [[Levitated dipole]] experiment:<ref>{{Cite journal|title=APS – 50th Annual Meeting of the Division of Plasma Physics – Event – Improved Confinement During Magnetic Levitation in LDX|url=https://meetings.aps.org/Meeting/DPP08/Session/CI1.6|journal=Bulletin of the American Physical Society|publisher=American Physical Society|volume=53|issue=14}}</ref> 0.26
# Spheromaks: ≈ 0.1,<ref name = "WHAT">{{cite journal | last1 = Ono | first1 = Y | year = 1999 | title = New relaxation of merging spheromaks to a field reversed configuration | journal = Nuclear Fusion | volume = 39 | issue = 11Y| pages = 2001–2008 | doi = 10.1088/0029-5515/39/11Y/346 | bibcode = 1999NucFu..39.2001O }}</ref> Maximum 0.2 based on Mercier limit.<ref>{{Cite web|last1=Fowler|first1=T. K.|last2=Hooper|first2=E. B.|date=1996-06-19|title=Advanced spheromak fusion reactor|url=https://digital.library.unt.edu/ark:/67531/metadc682204/|access-date=2020-10-11|website=ICENES `96: emerging nuclear energy systems, Obninsk (Russian Federation), Jun 1996|language=en}}</ref>
# The [[DIII-D]] machine: 0.126 {{Citation needed|date=March 2015}}
# The [[Gas Dynamic Trap]] a magnetic mirror: 0.6<ref>{{cite journal|title=Three Game Changing Discoveries: A Simpler Fusion Concept?|first=Thomas C.|last=Simonen|s2cid=122088138|journal=Journal of Fusion Energy|date=2016|volume=35|pages=63–68|doi=10.1007/s10894-015-0017-2}}</ref> for 5E−3 seconds.<ref name="Present">Gas Dynamic Trap (GDT). Experiments with Electron Heating. Budker Institute of Nuclear Physics, Novosibirsk State University. Siberian Branch, Russia, 2012, Thomas Simonen</ref>
# The Sustained Spheromak Plasma Experiment at Los Alamos National labs < 0.05 for 4E−6 seconds.<ref>{{Cite journal|last1=Wood|first1=R.D.|last2=Hill|first2=D.N.|last3=McLean|first3=H.S.|last4=Hooper|first4=E. B.|last5=Hudson|first5=B.F.|last6=Moller|first6=J.M.|last7=Romero-Talamás|first7=C.A.|date=2008-12-30|title=Improved magnetic field generation efficiency and higher temperature spheromak plasmas|url=http://dx.doi.org/10.1088/0029-5515/49/2/025001|journal=Nuclear Fusion|volume=49|issue=2|pages=025001|doi=10.1088/0029-5515/49/2/025001|osti=947748|issn=0029-5515}}</ref>
-->

== See also ==
{{Portal|Energy|Nuclear technology}}{{cols}}
* [[COLEX process]], for production of Li-6
* [[Fusion ignition]]
* [[High beta fusion reactor]]
* [[Inertial electrostatic confinement]]
* [[Levitated dipole]]
* [[List of fusion experiments]]
* [[Magnetic mirror]]
* [[Starship]]
{{colend}}

== References ==
{{Reflist|refs=
<ref name="ProliferationRisk_Goldston">R. J. Goldston, A. Glaser, A. F. Ross: [http://web.mit.edu/fusion-fission/HybridsPubli/Fusion_Proliferation_Risks.pdf "Proliferation Risks of Fusion Energy: Clandestine Production, Covert Production, and Breakout"] {{Webarchive|url=https://web.archive.org/web/20140227005532/http://web.mit.edu/fusion-fission/HybridsPubli/Fusion_Proliferation_Risks.pdf |date=2014-02-27  }};''9th IAEA Technical Meeting on Fusion Power Plant Safety'' (accessible at no cost, 2013) and {{Cite journal|last1=Glaser|first1=A.|last2=Goldston|first2=R. J.|doi= 10.1088/0029-5515/52/4/043004|title= Proliferation risks of magnetic fusion energy: Clandestine production, covert production and breakout|journal=Nuclear Fusion|volume=52|issue=4|at=043004|year=2012|bibcode= 2012NucFu..52d3004G|s2cid=73700489 }}</ref>
<ref name="StrongNeutronSources">{{cite conference|url= http://www.ianus.tu-darmstadt.de/media/ianus/pdfs/matthias/Strong_Neutron_Sources_final.pdf|title=Strong Neutron Sources – How to cope with weapon material production capabilities of fusion and spallation neutron sources?|url-status=dead|archive-url= https://web.archive.org/web/20140224024536/http://www.ianus.tu-darmstadt.de/media/ianus/pdfs/matthias/Strong_Neutron_Sources_final.pdf|archive-date=2014-02-24|first1=Matthias|last1=Englert|first2=Giorgio|last2=Franceschini|first3=Wolfgang|last3=Liebert|date=2011|conference=7th INMM/Esarda Workshop, Aix-en-Provence}}</ref>
}}

== Bibliography ==
* {{cite book|first=Daniel |last=Clery|title=A Piece of the Sun: The Quest for Fusion Energy|url={{google books |plainurl=y |id=EGcjCQAAQBAJ&|page=1}}|date=2014|publisher=The Overlook Press|isbn=978-1468310412}}
* {{cite book|last1=Cockburn |first1=Stewart |last2=Ellyard |first2=David |title=Oliphant, the life and times of Sir Mark Oliphant |date=1981 |publisher=Axiom Books |isbn=978-0959416404}}
* {{cite book|first=Stephen O. |last=Dean|title=Search for the Ultimate Energy Source: A History of the U.S. Fusion Energy Program|url={{google books |plainurl=y |id=KSA_AAAAQBAJ|page=212}}|date= 2013|publisher=Springer Science & Business Media|isbn=978-1461460374}}
* {{cite book|last1=Hagelstein |first1=Peter L. |author-link=Peter L. Hagelstein |last2=McKubre |first2=Michael |author-link2=Michael McKubre|last3=Nagel |first3=David |last4=Chubb |first4=Talbot |last5=Hekman |first5=Randall |title=11th Condensed Matter Nuclear Science |chapter=New Physical Effects in Metal Deuterides |ref={{harvid|Hagelstein et al.|2004}} |location=Washington |publisher=US Department of Energy |date=2004  |volume=11 |pages=23–59 |doi=10.1142/9789812774354_0003 |bibcode=2006cmns...11...23H |isbn=978-9812566409 |citeseerx=10.1.1.233.5518 |chapter-url=http://www.science.doe.gov/Sub/Newsroom/News_Releases/DOE-SC/2004/low_energy/Appendix_1.pdf |url-status=dead |archive-url=https://web.archive.org/web/20070106185101/http://www.science.doe.gov/Sub/Newsroom/News_Releases/DOE-SC/2004/low_energy/Appendix_1.pdf |archive-date=January 6, 2007 }} (manuscript)
* {{cite magazine|last=Hutchinson|first=Alex|title=The Year in Science: Physics|magazine=Discover Magazine (Online)|date=January 8, 2006|url=http://discovermagazine.com/2006/jan/physics|access-date=2008-06-20|issn=0274-7529}}
* Nuttall, William J., Konishi, Satoshi, Takeda, Shutaro, and Webbe-Wood, David (2020). ''[https://books.google.com/books?id=QVUvzgEACAAJ Commercialising Fusion Energy: How Small Businesses are Transforming Big Science]''. IOP Publishing. {{ISBN|978-0750327176}}.
* {{cite book|first=Andrés de Bustos |last=Molina|title=Kinetic Simulations of Ion Transport in Fusion Devices|url={{google books |plainurl=y |id=adMWmwEACAAJ}}|date= 2013|publisher=Springer International Publishing|isbn=978-3319004211}}
* {{cite book|last=Nagamine|first=Kanetada|date=2003|title=Introductory Muon Science|publisher=Cambridge University Press|chapter=Muon Catalyzed Fusion|isbn=978-0521038201}}
* {{cite book|last=Pfalzner|first=Susanne|title=An Introduction to Inertial Confinement Fusion|date=2006|publisher=Taylor & Francis|location=US|isbn=978-0750307017}}

==Further reading==
* {{Cite magazine|last=Ball|first=Philip|magazine=[[Nature (magazine)|Nature]]|title=The chase for fusion energy|url=https://www.nature.com/immersive/d41586-021-03401-w/index.html|access-date=2021-11-22 |language=en}}
* [[Naomi Oreskes|Oreskes, Naomi]], "Fusion's False Promise: Despite a recent advance, [[nuclear fusion]] is not the solution to the [[climate crisis]]", ''[[Scientific American]]'', vol. 328, no. 6 (June 2023), p.&nbsp;86.

== External links ==
{{commons category|Nuclear fusion reactors}}
* [https://nucleus.iaea.org/sites/fusionportal/Pages/FusDIS.aspx Fusion Device Information System]
* [https://www.fusionenergybase.com/ Fusion Energy Base]
* [https://www.fusionindustryassociation.org/ Fusion Industry Association]
* [https://www.psatellite.com/fusion-power-and-propulsion-in-the-news/ Princeton Satellite Systems News]
* [https://web.archive.org/web/20190105193140/https://science.energy.gov/fes/ U.S. Fusion Energy Science Program]

{{Fusion power}}
{{Nuclear Technology}}
{{emerging technologies|energy=yes}}

[[Category:Fusion power| ]]
[[Category:Sustainable energy]]