Editing Tokamak (section)

=== First steps ===
In 1934, [[Mark Oliphant]], [[Paul Harteck]] and [[Ernest Rutherford]] were the first to achieve fusion on Earth, using a [[particle accelerator]] to shoot [[deuterium]] nuclei into metal foil containing deuterium or other atoms.<ref>{{cite journal |url=http://www.chemteam.info/Chem-History/Rutherford-1934b/Rutherford-1934b.html |title= Transmutation Effects Observed with Heavy Hydrogen |first1=Mark |last1= Oliphant |first2=Paul |last2=Harteck |first3= Ernest |last3= Rutherford |journal= Proceedings of the Royal Society |volume=144 |issue= 853 |pages=692–703 |date=1934 |doi=10.1098/rspa.1934.0077 |doi-access=free |bibcode= 1934RSPSA.144..692O }}</ref> This allowed them to measure the [[nuclear cross section]] of various fusion reactions, and determined that the deuterium–deuterium reaction occurred at a lower energy than other reactions, peaking at about 100,000&nbsp;[[electronvolt]]s (100&nbsp;keV).{{sfn|McCracken|Stott|2012|p=35}}{{efn|D–T fusion occurs at even lower energies, but [[tritium]] was unknown at the time. Their work created tritium, but they did not separate it chemically to demonstrate its existence. This was performed by [[Luis Walter Alvarez|Luis Alvarez]] and [[Robert Cornog]] in 1939.<ref>{{cite journal|doi=10.1103/PhysRev.56.613|title=Helium and Hydrogen of Mass 3|date=1939|last1=Alvarez|first1=Luis|last2=Cornog|first2=Robert|journal=Physical Review|volume=56|issue=6|page=613|bibcode = 1939PhRv...56..613A }}</ref>}}

Accelerator-based fusion is not practical because the reactor [[cross section (physics)|cross section]] is tiny; most of the particles in the accelerator will scatter off the fuel, not fuse with it. These scatterings cause the particles to lose energy to the point where they can no longer undergo fusion. The energy put into these particles is thus lost, and it is easy to demonstrate this is much more energy than the resulting fusion reactions can release.{{sfn|McCracken|Stott|2012|pp=36–38}}

To maintain fusion and produce net energy output, the bulk of the fuel must be raised to high temperatures so its atoms are constantly colliding at high speed; this gives rise to the name ''[[Nuclear fusion|thermonuclear]]'' due to the high temperatures needed to bring it about. In 1944, [[Enrico Fermi]] calculated the reaction would be self-sustaining at about 50,000,000 K; at that temperature, the rate that energy is given off by the reactions is high enough that they heat the surrounding fuel rapidly enough to maintain the temperature against losses to the environment, continuing the reaction.{{sfn|McCracken|Stott|2012|pp=36–38}}

During the [[Manhattan Project]], the first practical way to reach these temperatures was created, using an [[atomic bomb]]. In 1944, Fermi gave a talk on the physics of fusion in the context of a then-hypothetical [[hydrogen bomb]]. However, some thought had already been given to a ''controlled'' fusion device, and [[James L. Tuck]] and [[Stanislaw Ulam]] had attempted such using [[shaped charge]]s driving a metal foil infused with deuterium, although without success.{{sfn|Bromberg|1982|p=18}}

The first attempts to build a practical fusion machine took place in the [[United Kingdom]], where [[George Paget Thomson]] had selected the [[pinch effect]] as a promising technique in 1945. After several failed attempts to gain funding, he gave up and asked two graduate students, Stanley (Stan) W. Cousins and Alan Alfred Ware (1924–2010<ref>{{cite web | url=https://web2.ph.utexas.edu/utphysicshistory/AlanAWare.html | title=UTPhysicsHistorySite | access-date=29 May 2022 | archive-date=29 May 2022 | archive-url=https://web.archive.org/web/20220529211017/https://web2.ph.utexas.edu/utphysicshistory/AlanAWare.html }}</ref>), to build a device out of surplus [[radar]] equipment. This was successfully operated in 1948, but showed no clear evidence of fusion and failed to gain the interest of the [[Atomic Energy Research Establishment]].{{sfn|Herman|1990|p=[https://archive.org/details/fusionsearchfore00herm/page/40 40]}}