Editing Nuclear fusion (section)

==History==
{{main|Timeline of nuclear fusion}}

=== Theory ===
[[File:EffetTunnel.gif|thumb|Animation of an electron's wave function as [[quantum tunneling]] allows transit through a barrier with a low probability. In the same fashion, an atomic nucleus can quantum tunnel through the [[Coulomb barrier]] to another nucleus, making a fusion reaction possible.]]
American chemist [[William Draper Harkins]] was the first to propose the concept of nuclear fusion in 1915.<ref name=":0">{{Cite journal
|author=Robert S. Mulliken
|author-link=Robert S. Mulliken
|year=1975
|url=http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/harkins-william-d.pdf
|title=William Draper Harkins 1873 - 1951
|journal=Biographical Memoirs
|volume=46
|pages=47–80
|publisher=National Academy of Sciences
|access-date=23 August 2023
|archive-date=10 May 2017
|archive-url=https://web.archive.org/web/20170510115525/http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/harkins-william-d.pdf
|url-status=live
}}</ref> [[Francis William Aston]]'s 1919 invention of the [[mass spectrometer]] allowed the discovery that four hydrogen atoms are heavier than one helium atom. Thus in 1920, [[Arthur Eddington]] correctly predicted fusion of hydrogen into helium could be the primary source of stellar energy.<ref>{{cite journal |last1=Eddington |first1=A.S. |title=The internal constitution of the stars |journal=Nature |date=2 September 1920 |volume=106 |issue=2653 |pages=14–20 |doi=10.1038/106014a0 |bibcode=1920Natur.106...14E |s2cid=36422819 |url=https://zenodo.org/record/1429642 |doi-access=free |access-date=25 March 2020 |archive-date=17 July 2022 |archive-url=https://web.archive.org/web/20220717115105/https://zenodo.org/record/1429642 |url-status=live }} 
*Reprinted in: {{cite journal |last1=Eddington |first1=A.S. |title=The internal constitution of the stars |journal=The Scientific Monthly |date=October 1920 |volume=11 |issue=4 |pages=297–303 |bibcode=1920SciMo..11..297E |url=https://babel.hathitrust.org/cgi/pt?id=hvd.32044102928264&view=1up&seq=313&skin=2021 |access-date=17 August 2022 |archive-date=17 August 2022 |archive-url=https://web.archive.org/web/20220817051553/https://babel.hathitrust.org/cgi/pt?id=hvd.32044102928264&view=1up&seq=313&skin=2021 |url-status=live }}
*Reprinted in: {{cite journal |last1=Eddington |first1=A.S. |title=The internal constitution of the stars |journal=The Observatory |date=October 1920 |volume=43 |issue=557 |pages=341–358 |bibcode=1920Obs....43..341E |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015011432153&view=1up&seq=347&skin=2021 |access-date=17 August 2022 |archive-date=17 August 2022 |archive-url=https://web.archive.org/web/20220817060446/https://babel.hathitrust.org/cgi/pt?id=mdp.39015011432153&view=1up&seq=347&skin=2021 |url-status=live }}</ref> 

[[Quantum tunneling]] was discovered by [[Friedrich Hund]] in 1927, with relation to electron levels.<ref>{{cite journal |last1=Hund |first1=F. |title=Zur Deutung der Molekelspektren. I. |journal=Zeitschrift für Physik |date=October 1927 |volume=40 |issue=10 |pages=742–764 |doi=10.1007/BF01400234 |bibcode=1927ZPhy...40..742H |s2cid=186239503 |trans-title=On the explanation of molecular spectra I. |language=German}}</ref><ref>Tunnelling was independently observed by Soviet scientists [[Grigory Samuilovich Landsberg]] and [[Leonid Isaakovich Mandelstam]]. See: 
*{{cite journal |last1=Ландсберг |first1=Г.С. |last2=Мандельштам |first2=Л.И. |title=Новое явление в рассеянии света (предварительный отчет) |journal=Журнал Русского физико-химического общества, Раздел физики [Journal of the Russian Physico-Chemical Society, Physics Section] |year=1928 |volume=60 |page=335 |trans-title=A new phenomenon in the scattering of light (preliminary report) |language=Russian}}
*{{cite journal |last1=Landsberg |first1=G. |last2=Mandelstam |first2=L. |title=Eine neue Erscheinung bei der Lichtzerstreuung in Krystallen |journal=Die Naturwissenschaften |year=1928 |volume=16 |issue=28 |pages=557–558 |doi=10.1007/BF01506807 |bibcode=1928NW.....16..557. |s2cid=22492141 |trans-title=A new phenomenon in the case of the scattering of light in crystals |language=German}}
*{{cite journal |last1=Landsberg |first1=G.S. |last2=Mandelstam |first2=L.I. |title=Über die Lichtzerstreuung in Kristallen |journal=Zeitschrift für Physik |year=1928 |volume=50 |issue=11–12 |pages=769–780 |doi=10.1007/BF01339412 |bibcode=1928ZPhy...50..769L |s2cid=119357805 |trans-title=On the scattering of light in crystals |language=German}}</ref> In 1928, [[George Gamow]] was the first to apply tunneling to the nucleus, first to [[alpha decay]], then to fusion as an inverse process. From this, in 1929, [[Robert d'Escourt Atkinson|Robert Atkinson]] and [[Fritz Houtermans]] made the first estimates for stellar fusion rates.<ref>{{Cite journal |last1=Abu-Shawareb |first1=H. |last2=Acree |first2=R. |last3=Adams |first3=P. |last4=Adams |first4=J. |last5=Addis |first5=B. |last6=Aden |first6=R. |last7=Adrian |first7=P. |last8=Afeyan |first8=B. B. |last9=Aggleton |first9=M. |last10=Aghaian |first10=L. |last11=Aguirre |first11=A. |last12=Aikens |first12=D. |last13=Akre |first13=J. |last14=Albert |first14=F. |last15=Albrecht |first15=M. |date=2024-02-05 |title=Achievement of Target Gain Larger than Unity in an Inertial Fusion Experiment |url=https://link.aps.org/doi/10.1103/PhysRevLett.132.065102 |journal=Physical Review Letters |language=en |volume=132 |issue=6 |page=065102 |doi=10.1103/PhysRevLett.132.065102 |pmid=38394591 |bibcode=2024PhRvL.132f5102A |issn=0031-9007}}</ref><ref>{{cite journal |last1=Atkinson |first1=R. d'E. |last2=Houtermans |first2=F. G. |title=Zur Frage der Aufbaumöglichkeit der Elemente in Sternen |journal=Zeitschrift für Physik |year=1929 |volume=54 |issue=9–10 |pages=656–665 |doi=10.1007/BF01341595 |bibcode=1929ZPhy...54..656A |s2cid=123658609 |trans-title=On the question of the possibility of forming elements in stars |language=German}}</ref>  

In 1938, [[Hans Bethe]] worked with [[Charles Critchfield]] to enumerate the [[proton–proton chain]] that dominates Sun-type stars. In 1939, Bethe published the discovery of the [[CNO cycle]] common to higher-mass stars. 

=== Early experiments ===
[[File:27-inch cyclotron.jpg|thumb|[[M. Stanley Livingston]] and [[Ernest Lawrence]] in front of UCRL's 27-inch [[cyclotron]] in 1934. These devices were used for many early experiments demonstrating deuterium fusion.]]
During the 1920s, [[Patrick Blackett]] made the first conclusive experiments in artificial [[nuclear transmutation]] at the [[Cavendish Laboratory]]. There, [[John Cockcroft]] and [[Ernest Walton]] built [[Cockcroft–Walton generator|their generator]] on the inspiration of Gamow's paper. In April 1932, they published experiments on the reaction: 

:{{nuclide|link=yes|lithium|7}} + [[Proton|p]] →  {{SimpleNuclide|X|8}} → 2 {{Nuclide|helium|4|link=yes}}
where the intermediary nuclide was later confirmed to be the extremely short-lived [[beryllium-8]].<ref name="b4852">{{cite journal |last1=COCKCROFT |first1=J. D. |last2=WALTON |first2=E. T. S. |year=1932 |title=Disintegration of Lithium by Swift Protons |url=https://www.nature.com/articles/129649a0.pdf |journal=Nature |publisher=Springer Science and Business Media LLC |volume=129 |issue=3261 |pages=649 |doi=10.1038/129649a0 |issn=0028-0836 |access-date=2025-02-19 |doi-access=free|bibcode=1932Natur.129..649C }}</ref> This has a claim to the first artificial fusion reaction.{{Citation needed|date=February 2025}} 

In papers from July and November 1933, [[Ernest Lawrence]] et. al. at the [[UCRL|University of California Radiation Laboratory]], in some of the earliest [[cyclotron]] experiments, accidentally produced the first [[Deuterium-deuterium fusion|deuterium-deuterium]] fusion reactions:  
: {{nuclide|Deuterium}} + {{nuclide|Deuterium}} → {{nuclide|Tritium}} + p
: {{nuclide|Deuterium}} + {{nuclide|Deuterium}} → {{nuclide|Helium|3}} + {{SubatomicParticle|10neutron}}

The Radiation Lab, only detecting the resulting energized protons and neutrons,<ref name="n665">{{cite journal |last1=Lawrence |first1=Ernest O. |last2=Livingston |first2=M. Stanley |last3=Lewis |first3=Gilbert N. |date=1933-07-01 |title=The Emission of Protons from Various Targets Bombarded by Deutons of High Speed |journal=Physical Review |volume=44 |issue=1 |pages=56 |doi=10.1103/PhysRev.44.56 |bibcode=1933PhRv...44...56L |issn=0031-899X}}</ref><ref name="m978">{{cite journal |last1=Livingston |first1=M. Stanley |last2=Henderson |first2=Malcolm C. |last3=Lawrence |first3=Ernest O. |date=1933-11-01 |title=Neutrons from Deutons and the Mass of the Neutron |journal=Physical Review |volume=44 |issue=9 |pages=781–782 |doi=10.1103/PhysRev.44.781 |bibcode=1933PhRv...44..781L |issn=0031-899X}}</ref> misinterpreted the source as an exothermic disintegration of the deuterons, now known to be impossible.<ref name="m343">{{cite journal |last=Lestone |first=J. P. |date=2024-09-02 |title=Some of the History Surrounding the Oliphant et al. Discovery of dd Fusion and an Inference of the d(d,p)t Cross Section from This 1934 Paper |journal=Fusion Science and Technology |volume=80 |issue=sup1 |page= |doi=10.1080/15361055.2024.2339644 |issn=1536-1055 |doi-access=free}}</ref> In May 1934, [[Mark Oliphant]], [[Paul Harteck]], and [[Ernest Rutherford]] at the Cavendish Laboratory,<ref name="v423">{{cite journal |date=1934 |title=Transmutation effects observed with heavy hydrogen |journal=Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character |volume=144 |issue=853 |pages=692–703 |doi=10.1098/rspa.1934.0077 |issn=0950-1207 |doi-access=free|bibcode=1934RSPSA.144..692O |last1=Oliphant |first1=M. L. E. |last2=Harteck |first2=P. |last3=Rutherford |first3=Lord }}</ref> published an intentional deuterium fusion experiment, and made the discovery of both [[tritium]] and [[helium-3]]. This is widely considered the first experimental demonstration of fusion.<ref name="m343" />

In 1938, Arthur Ruhlig at the [[University of Michigan]] made the first observation of [[deuterium–tritium fusion|deuterium–tritium (DT) fusion]] and its characteristic 14 MeV neutrons, now known as the most favourable reaction: 
: {{nuclide|Deuterium}} + {{nuclide|Tritium}} →  {{nuclide|Helium|4}} + {{SubatomicParticle|10neutron}}
=== Weaponization ===
{{Main page|Nuclear weapon design|Thermonuclear weapon}}
Research into [[Thermonuclear weapon|fusion for military purposes]] began in the early 1940s as part of the [[Manhattan Project]]. In 1941, Enrico Fermi and Edward Teller had a conversation about the possibility of a fission bomb creating conditions for thermonuclear fusion. In 1942, [[Emil Konopinski]] brought Ruhlig's work on the deuterium-tritium reaction to the projects attention. [[J. Robert Oppenheimer]] initially commissioned physicists at Chicago and Cornell to use the Harvard University cyclotron to secretly investigate its cross-section, and that of the lithium reaction (see below). Measurements were obtained at Purdue, Chicago, and Los Alamos from 1942-1946. Theoretical assumptions about DT fusion gave it a similar cross-section to DD. However, in 1946 [[Egon Bretscher]] discovered a [[Resonance (particle physics)|resonance]] enhancement giving the DT reaction a cross-section ~100 times larger.<ref name="r126">{{cite journal |last1=Chadwick |first1=M. B. |last2=Reed |first2=B. Cameron |date=2024-09-02 |title=Introduction to Special Issue on the Early History of Nuclear Fusion |journal=Fusion Science and Technology |volume=80 |issue=sup1 |page= |doi=10.1080/15361055.2024.2346868 |issn=1536-1055 |doi-access=free|bibcode=2024FuST...80D...3C }}</ref>

From 1945, John von Neumann, Teller, and other Los Alamos scientists used [[ENIAC]], one of the first electronic computers, to simulate thermonuclear weapon detonations.<ref name="c888">{{cite journal |date=2014-09-30 |title=Los Alamos Bets on ENIAC: Nuclear Monte Carlo Simulations, 1947-1948 |url=https://ieeexplore.ieee.org/document/6880250 |access-date=2025-03-05 |journal=IEEE Annals of the History of Computing|doi=10.1109/MAHC.2014.40 |last1=Haigh |first1=Thomas |last2=Priestley |first2=Mark |last3=Rope |first3=Crispin |volume=36 |issue=3 |pages=42–63 }}</ref>

The first artificial thermonuclear fusion reaction occurred during the 1951 US [[Greenhouse Item|Greenhouse George]] nuclear test, using a small amount of [[Deuterium–tritium fusion|deuterium–tritium]] gas. This produced the largest yield to date, at 225 kt, 15 times that of [[Little Boy]]. The first "true" [[thermonuclear weapon]] detonation i.e. a two-stage device, was the 1952 [[Ivy Mike]] test of a [[Liquid hydrogen|liquid]] [[Deuterium fusion|deuterium-fusing]] device, yielding over 10 Mt. The key to this jump was the full utilization of the fission blast by the [[Teller-Ulam]] design.

The Soviet Union had begun their focus on a hydrogen bomb program earlier, and in 1953 carried out the [[RDS-6s]] test. This had international impacts as the first air-deliverable bomb using fusion, but yielded 400 kt and was limited by its single-stage design. The first Soviet two-stage test was [[RDS-37]] in 1955 yielding 1.5 Mt, using an independently-reached version of the Teller-Ulam design.

Modern devices benefit from the usage of solid [[lithium deuteride]] with an enrichment of lithium-6. This is due to the [[Jetter cycle]] involving the exothermic reaction:

:{{nuclide|link=yes|lithium|6}} + {{SubatomicParticle|10neutron}} → {{nuclide|Helium|4}} + {{nuclide|Tritium}}
During thermonuclear detonations, this provides tritium for the highly energetic DT reaction, and benefits from its neutron production, creating a closed neutron cycle.<ref name="m027">{{cite arXiv |last1=Fortunato |first1=Lorenzo |last2=Loaiza |first2=Andres Felipe Lopez |last3=Albertin |first3=Giulio |last4=Fragiacomo |first4=Enrico |date=2024-09-30 |title=Jetter and Post nuclear fusion cycles: new fire to an old idea |class=physics.plasm-ph |eprint=2410.09065 }}</ref>

=== Fusion energy ===
While fusion bomb detonations were [[Project PACER#Development|loosely considered for energy production]], the possibility of controlled and sustained reactions remained the scientific focus for peaceful fusion power. Research into developing controlled fusion inside [[fusion reactors]] has been ongoing since the 1930s, with [[Los Alamos National Laboratory]]'s Scylla I device producing the first laboratory thermonuclear fusion in 1958, but the technology is still in its developmental phase.<ref>{{Cite news |last=Videmšek |first=Boštjan |date=30 May 2022 |title=Nuclear fusion could give the world a limitless source of clean energy. We're closer than ever to it |publisher=CNN |url=https://www.cnn.com/interactive/2022/05/world/iter-nuclear-fusion-climate-intl-cnnphotos/ |access-date=13 December 2022 |archive-date=13 December 2022 |archive-url=https://web.archive.org/web/20221213004108/https://www.cnn.com/interactive/2022/05/world/iter-nuclear-fusion-climate-intl-cnnphotos/ |url-status=live }}</ref>

The first experiments producing large amounts of controlled fusion power were the experiments with mixes of deuterium and tritium in [[Tokamaks]]. 
Experiments in the [[Tokamak Fusion Test Reactor | TFTR]] at the
[[ Princeton Plasma Physics Laboratory | PPPL]] in [[Princeton University]]
Princeton NJ, USA during 1993-1996 produced created 1.6 GJ fusion energy.
The peak fusion power was 10.3 MW from 3.7 x 10<sup>18</sup> reactions per second, 
and peak fusion energy created in one discharge was 7.6 MJ. 
Subsequent experiments in the [[Joint European Torus | JET]] in 1997 achieved a peak 
fusion power of 16 MW (5.8 x 10 <sup>18</sup>/s).
The central Q, defined as the local fusion power produced to the local applied heating power, is computed to be 1.3.
<ref>"Core fusion power gain and alpha heating in JET, TFTR, and ITER",
R.V. Budny, J.G. Cordey and TFTR Team and JET Contributors,
Nuclear Fus. (2016) <56> 056002 #5 (May)
https://iopscience.iop.org/article/10.1088/0029-5515/56/5/056002
//home/budny/papers/NF/core_q_dt/nf_56_5_056002.pdf</ref>
A JET experiment in 2024 produced 69 MJ of fusion power, consuming 0.2 mgm of D and T.


The US [[National Ignition Facility]], which uses laser-driven [[inertial confinement fusion]], was designed with a goal of achieving a [[fusion energy gain factor]] (Q) of larger than one; the first large-scale laser target experiments were performed in June 2009 and ignition experiments began in early 2011.<ref name="programsNIF">{{cite journal |author=Moses, E. I. |year=2009 |title=The National Ignition Facility: Ushering in a new age for high energy density science |url=https://zenodo.org/record/1232045 |journal=Physics of Plasmas |volume=16 |issue=4 |pages=041006 |bibcode=2009PhPl...16d1006M |doi=10.1063/1.3116505 |access-date=25 March 2020 |archive-date=12 August 2020 |archive-url=https://web.archive.org/web/20200812160458/https://zenodo.org/record/1232045 |url-status=live }}</ref><ref>{{cite journal |author=Kramer, David |date=March 2011 |title=DOE looks again at inertial fusion as potential clean-energy source |journal=Physics Today |volume=64 |issue=3 |pages=26–28 |bibcode=2011PhT....64c..26K |doi=10.1063/1.3563814}}</ref>  On 13 December 2022, the [[United States Department of Energy]] announced that on 5 December 2022, they had successfully accomplished break-even fusion, "delivering&nbsp;2.05&nbsp;megajoules (MJ) of energy to the target, resulting in&nbsp;3.15 MJ of fusion energy output."<ref>{{cite web |title=DOE National Laboratory Makes History by Achieving Fusion Ignition |date=13 December 2022 |url=https://www.energy.gov/articles/doe-national-laboratory-makes-history-achieving-fusion-ignition |access-date=13 December 2022 |archive-date=19 February 2023 |archive-url=https://web.archive.org/web/20230219060607/https://www.energy.gov/articles/doe-national-laboratory-makes-history-achieving-fusion-ignition |url-status=live }}</ref> The rate of supplying power to the experimental test cell is hundreds of times larger than the power delivered to the target.

Prior to this breakthrough, controlled fusion reactions had been unable to produce break-even (self-sustaining) controlled fusion.<ref>{{cite web |title=Progress in Fusion |url=http://www.iter.org/sci/beyonditer |access-date=15 February 2010 |publisher=[[ITER]] |archive-date=1 June 2010 |archive-url=https://web.archive.org/web/20100601070234/http://www.iter.org/sci/BeyondITER |url-status=live }}</ref> The two most advanced approaches for it are [[Magnetic confinement fusion|magnetic confinement]] (toroid designs) and inertial confinement (laser designs). Workable designs for a toroidal reactor that theoretically will deliver ten times more fusion energy than the amount needed to heat plasma to the required temperatures are in development (see [[ITER]]). The ITER facility is expected to finish its construction phase in 2025. It will start commissioning the reactor that same year and initiate plasma experiments in 2025, but is not expected to begin full deuterium–tritium fusion until 2035.<ref>{{cite web |year=2014 |title=ITER – the way to new energy |url=http://www.iter.org/proj/iterandbeyond |url-status=dead |archive-url=https://web.archive.org/web/20120922162049/http://www.iter.org/proj/iterandbeyond |archive-date=22 September 2012 |website=ITER}}</ref>

Private companies pursuing the commercialization of nuclear fusion received $2.6 billion in private funding in 2021 alone, going to many notable startups including but not limited to [[Commonwealth Fusion Systems]], [[Helion Energy|Helion Energy Inc]]., [[General Fusion]], [[TAE Technologies]] Inc. and [[Zap Energy]] Inc.<ref>{{Cite news |date=2022-12-14 |title=Nuclear Fusion Breakthrough Set to Send Billions of Dollars Flowing to Atomic Startups |language=en |work=Bloomberg.com |url=https://www.bloomberg.com/news/articles/2022-12-14/fusion-milestone-draws-billions-to-replicate-power-of-the-stars |access-date=2023-01-10 |archive-date=31 January 2023 |archive-url=https://web.archive.org/web/20230131083723/https://www.bloomberg.com/news/articles/2022-12-14/fusion-milestone-draws-billions-to-replicate-power-of-the-stars |url-status=live |author-last1=Wade|author-first1=Will}}</ref>

One of the most recent breakthroughs to date in maintaining a sustained fusion reaction occurred in France's WEST fusion reactor. It maintained a 90 million degree plasma for a record time of six minutes. This is a tokamak style reactor which is the same style as the upcoming ITER reactor.<ref>{{Cite web |last=McGrath |first=Jenny |date=2024-05-07 |title=Fusion Breakthrough: 6 Minutes of Plasma Sets New Reactor Record |url=https://www.sciencealert.com/fusion-breakthrough-6-minutes-of-plasma-sets-new-reactor-record |access-date=2024-09-27 |website=ScienceAlert |language=en-US}}</ref>