Editing Nuclear fusion (section)

== Artificial fusion ==
{{main article|Fusion power}}

=== Thermonuclear fusion ===
{{unreferenced section|date=August 2023}}
Thermonuclear fusion is the process of atomic nuclei combining or "fusing" using high temperatures to drive them close enough together for this to become possible. Such temperatures cause the matter to become a [[plasma physics|plasma]] and, if confined, fusion reactions may occur due to collisions with extreme thermal kinetic energies of the particles. There are two forms of thermonuclear fusion: ''uncontrolled'', in which the resulting energy is released in an uncontrolled manner, as it is in [[thermonuclear weapon]]s ("hydrogen bombs") and in most [[star]]s; and ''controlled'', where the fusion reactions take place in an environment allowing some or all of the energy released to be harnessed.

Temperature is a measure of the average [[kinetic energy]] of particles, so by heating the material it will gain energy. After reaching sufficient temperature, given by the [[Lawson criterion]], the energy of accidental collisions within the [[plasma (physics)|plasma]] is high enough to overcome the [[Coulomb barrier]] and the particles may fuse together.

In a [[Deuterium–tritium fusion|deuterium–tritium fusion reaction]], for example, the energy necessary to overcome the [[Coulomb barrier]] is 0.1&nbsp;[[Electronvolt|MeV]]. Converting between energy and temperature shows that the 0.1 MeV barrier would be overcome at a temperature [[Orders of magnitude (temperature)|in excess of 1.2 billion]] [[kelvin]].

There are two effects that are needed to lower the actual temperature. One is the fact that [[temperature]] is the ''average'' kinetic energy, implying that some nuclei at this temperature would actually have much higher energy than 0.1&nbsp;MeV, while others would be much lower. It is the nuclei in the high-energy tail of the [[Distribution function (physics)|velocity distribution]] that account for most of the fusion reactions. The other effect is [[quantum tunnelling]]. The nuclei do not actually have to have enough energy to overcome the Coulomb barrier completely. If they have nearly enough energy, they can tunnel through the remaining barrier. For these reasons fuel at lower temperatures will still undergo fusion events, at a lower rate.

''Thermonuclear'' fusion is one of the methods being researched in the attempts to produce [[fusion power]]. If thermonuclear fusion becomes favorable to use, it would significantly reduce the world's [[carbon footprint]].

=== Beam–beam or beam–target fusion ===
{{main|Colliding beam fusion}}

Accelerator-based light-ion fusion is a technique using [[particle accelerator]]s to achieve particle kinetic energies sufficient to induce light-ion fusion reactions.<ref>{{Cite book |url=https://link.springer.com/book/10.1007/978-3-030-62308-1 |title=Accelerator Technology |series=Particle Acceleration and Detection |year=2020 |language=en |doi=10.1007/978-3-030-62308-1 |isbn=978-3-030-62307-4 |s2cid=229610872 |last1=Möller |first1=Sören |access-date=20 September 2022 |archive-date=23 September 2022 |archive-url=https://web.archive.org/web/20220923225830/https://link.springer.com/book/10.1007/978-3-030-62308-1 |url-status=live }}</ref>

Accelerating light ions is relatively easy, and can be done in an efficient manner—requiring only a vacuum tube, a pair of electrodes, and a high-voltage transformer; fusion can be observed with as little as 10 kV between the electrodes.{{citation needed|date=August 2023}} The system can be arranged to accelerate ions into a static fuel-infused target, known as ''beam–target'' fusion, or by accelerating two streams of ions towards each other, ''beam–beam'' fusion.{{citation needed|date=August 2023}} The key problem with accelerator-based fusion (and with cold targets in general) is that fusion cross sections are many orders of magnitude lower than Coulomb interaction cross-sections. Therefore, the vast majority of ions expend their energy emitting [[bremsstrahlung]] radiation and the ionization of atoms of the target. Devices referred to as sealed-tube [[neutron generator]]s are particularly relevant to this discussion. These small devices are miniature particle accelerators filled with deuterium and tritium gas in an arrangement that allows ions of those nuclei to be accelerated against hydride targets, also containing deuterium and tritium, where fusion takes place, releasing a flux of neutrons. Hundreds of neutron generators are produced annually for use in the petroleum industry where they are used in measurement equipment for locating and mapping oil reserves.{{citation needed|date=August 2023}}

A number of attempts to recirculate the ions that "miss" collisions have been made over the years. One of the better-known attempts in the 1970s was [[Migma]], which used a unique particle [[storage ring]] to capture ions into circular orbits and return them to the reaction area. Theoretical calculations made during funding reviews pointed out that the system would have significant difficulty scaling up to contain enough fusion fuel to be relevant as a power source. In the 1990s, a new arrangement using a [[field-reversed configuration]] (FRC) as the storage system was proposed by [[Norman Rostoker]] and continues to be studied by [[TAE Technologies]] {{as of|2021|lc=yes}}. A closely related approach is to merge two FRC's rotating in opposite directions,<ref>J. Slough, G. Votroubek, and C. Pihl, "Creation of a high-temperature plasma through merging and compression of supersonic field reversed configuration plasmoids" Nucl. Fusion 51,053008 (2011).</ref> which is being actively studied by [[Helion Energy]]. Because these approaches all have ion energies well beyond the [[Coulomb barrier]], they often suggest the use of alternative fuel cycles like p-[[Boron#Depleted boron (boron-11)|<sup>11</sup>B]] that are too difficult to attempt using conventional approaches.<ref>A. Asle Zaeem et al "Aneutronic Fusion in Collision of Oppositely Directed Plasmoids" Plasma Physics Reports, Vol. 44, No. 3, pp. 378–386 (2018).</ref>

==== Element synthesis ====
{{See also|Superheavy element}}
Fusion of very heavy target nuclei with accelerated ion beams is the primary method of element synthesis. In early 1930s nuclear experiments, deuteron beams were used, to discover the first synthetic elements, such as [[technetium]], [[neptunium]], and [[plutonium]]:

<math chem="">\begin{align}
\ce{ {^{238}_{92}U} + {^{2}_{1}H} ->} &\ce{ {^{238}_{93}Np} + 2^{1}_{0}n}
\end{align}</math>

Fusion of very heavy target nuclei with heavy ion beams has been used to discover [[Superheavy element|superheavy elements]]:

<math chem="">\begin{align}
\ce{ {^{208}_{82}Pb} + {^{62}_{28}Ni} ->} &\ce{ {^{269}_{110}Ds} + ^{1}_{0}n}
\end{align}</math>

<math chem="">\begin{align}
\ce{ {^{249}_{98}Cf} + {^{48}_{20}Ca} ->} &\ce{ {^{294}_{118}Og} + 3^{1}_{0}n}
\end{align}</math>

=== Muon-catalyzed fusion ===
[[Muon-catalyzed fusion]] is a fusion process that occurs at ordinary temperatures. It was studied in detail by [[Steven E. Jones|Steven Jones]] in the early 1980s. Net energy production from this reaction has been unsuccessful because of the high energy required to create [[muon]]s, their short 2.2&nbsp;μs [[half-life]], and the high chance that a muon will bind to the new [[alpha particle]] and thus stop catalyzing fusion.<ref>{{cite journal |author=Jones, S.E. |title=Muon-Catalysed Fusion Revisited |journal=Nature |volume=321 |pages=127–133 |year=1986 |doi=10.1038/321127a0|bibcode = 1986Natur.321..127J |issue=6066|s2cid=39819102 }}</ref>

=== Other principles ===
[[File:TCV vue gen.jpg|thumb|The ''[[Tokamak à configuration variable]]'', research fusion reactor, at the [[École Polytechnique Fédérale de Lausanne]] (Switzerland)]]

Some other confinement principles have been investigated.
* [[Antimatter catalyzed nuclear pulse propulsion|Antimatter-initialized fusion]] uses small amounts of [[antimatter]] to trigger a tiny fusion explosion. This has been studied primarily in the context of making [[nuclear pulse propulsion]], and [[pure fusion bomb]]s feasible. This is not near becoming a practical power source, due to the cost of manufacturing antimatter alone.
* [[Pyroelectric fusion]] was reported in April 2005 by a team at [[University of California, Los Angeles|UCLA]]. The scientists used a [[pyroelectricity|pyroelectric]] crystal heated from {{convert|-34|to|7|C|F}}, combined with a [[tungsten]] needle to produce an [[electric field]] of about 25&nbsp;gigavolts per meter to ionize and accelerate [[deuterium]] nuclei into an [[erbium]] deuteride target. At the estimated energy levels,<ref>[http://www.nature.com/nature/journal/v434/n7037/suppinfo/nature03575.html Supplementary methods for "Observation of nuclear fusion driven by a pyroelectric crystal"] {{Webarchive|url=https://web.archive.org/web/20170204193327/http://www.nature.com/nature/journal/v434/n7037/suppinfo/nature03575.html |date=4 February 2017 }}. Main article {{cite journal|doi=10.1038/nature03575|title=Observation of nuclear fusion driven by a pyroelectric crystal|year=2005|last1=Naranjo|first1=B.|last2=Gimzewski|first2=J.K.|last3=Putterman|first3=S.|journal=Nature|volume=434|issue=7037|pages=1115–1117|pmid=15858570|bibcode = 2005Natur.434.1115N |s2cid=4407334}}</ref> the D–D fusion reaction may occur, producing [[helium-3]] and a 2.45&nbsp;MeV [[neutron]]. Although it makes a useful neutron generator, the apparatus is not intended for power generation since it requires far more energy than it produces.<ref>[http://rodan.physics.ucla.edu/pyrofusion/ UCLA Crystal Fusion]. Rodan.physics.ucla.edu. Retrieved 17 August 2011. {{webarchive |url=https://web.archive.org/web/20150608184332/http://rodan.physics.ucla.edu/pyrofusion/ |date=8 June 2015 }}</ref><ref>{{cite journal |url=http://www.aip.org/pnu/2005/split/729-1.html |title=Pyrofusion: A Room-Temperature, Palm-Sized Nuclear Fusion Device |author1=Schewe, Phil |author2=Stein, Ben |name-list-style=amp |journal=Physics News Update |volume=729 |issue=1 |year=2005 |url-status=dead |archive-url=https://web.archive.org/web/20131112155702/http://www.aip.org/pnu/2005/split/729-1.html |archive-date=12 November 2013 |accessdate=3 May 2006 }}</ref><ref>[http://www.csmonitor.com/2005/0606/p25s01-stss.html Coming in out of the cold: nuclear fusion, for real] {{Webarchive|url=https://web.archive.org/web/20120122115832/http://www.csmonitor.com/2005/0606/p25s01-stss.html |date=22 January 2012 }}. ''The Christian Science Monitor''. (6 June 2005). Retrieved 17 August 2011.</ref><ref>[http://www.nbcnews.com/id/7654627 Nuclear fusion on the desktop ... really!] {{Webarchive|url=https://web.archive.org/web/20160904023602/http://www.nbcnews.com/id/7654627/ |date=4 September 2016 }}. MSNBC (27 April 2005). Retrieved 17 August 2011.</ref> D–T fusion reactions have been observed with a tritiated erbium target.<ref>{{cite journal|doi=10.1016/j.nima.2010.08.003|title=Pyroelectric fusion using a tritiated target|journal=Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment|volume=632|issue=1|pages=43–46|year=2011|last1=Naranjo|first1=B.|last2=Putterman|first2=S.|last3=Venhaus|first3=T.|bibcode=2011NIMPA.632...43N}}</ref>
* [[Nuclear fusion–fission hybrid]] (hybrid nuclear power) is a proposed means of generating [[Electrical power industry|power]] by use of a combination of nuclear fusion and [[Nuclear fission|fission]] processes. The concept dates to the 1950s, and was briefly advocated by [[Hans Bethe]] during the 1970s, but largely remained unexplored until a revival of interest in 2009, due to the delays in the realization of pure fusion.<ref name="hybrid">{{cite journal | author = Gerstner, E. | title = Nuclear energy: The hybrid returns | year = 2009 | journal = [[Nature (journal)|Nature]] | volume = 460 | issue = 7251| pages = 25–28 | pmid = 19571861|doi=10.1038/460025a| doi-access = free }}</ref>
* [[Project PACER]], carried out at [[Los Alamos National Laboratory]] (LANL) in the mid-1970s, explored the possibility of a fusion power system that would involve exploding small [[H-bomb|hydrogen bomb]]s (fusion bombs) inside an underground cavity. As an energy source, the system is the only fusion power system that could be demonstrated to work using existing technology. However, it would also require a large, continuous supply of nuclear bombs, making the economics of such a system rather questionable.
* [[Bubble fusion]] also called '''sonofusion''' was a proposed mechanism for achieving fusion via [[sonic cavitation]] which rose to prominence in the early 2000s. Subsequent attempts at replication failed and the principal investigator, [[Rusi Taleyarkhan]], was judged guilty of [[research misconduct]] in 2008.<ref>{{cite news |last1=Maugh II |first1=Thomas |title=Physicist is found guilty of misconduct |url=https://www.latimes.com/archives/la-xpm-2008-jul-19-sci-misconduct19-story.html |access-date=17 April 2019 |work=Los Angeles Times |archive-date=17 April 2019 |archive-url=https://web.archive.org/web/20190417184641/https://www.latimes.com/archives/la-xpm-2008-jul-19-sci-misconduct19-story.html |url-status=live }}</ref>