Editing Nuclear fusion (section)

==Confinement in thermonuclear fusion==
The key problem in achieving thermonuclear fusion is how to confine the hot plasma. Due to the high temperature, the plasma cannot be in direct contact with any solid material, so it has to be located in a [[vacuum]]. Also, high temperatures imply high pressures. The plasma tends to expand immediately and some force is necessary to act against it. This force can take one of three forms: gravitation in stars, magnetic forces in magnetic confinement fusion reactors, or [[inertia]]l as the fusion reaction may occur before the plasma starts to expand, so the plasma's inertia is keeping the material together.

=== Gravitational confinement ===
{{main|Stellar nucleosynthesis}}{{unreferenced section|date=August 2023}}
One force capable of confining the fuel well enough to satisfy the [[Lawson criterion]] is [[gravity]]. The mass needed, however, is so great that gravitational confinement is only found in [[star]]s—the least massive stars capable of sustained fusion are [[red dwarf]]s, while [[brown dwarf]]s are able to fuse [[deuterium]] and [[lithium]] if they are of sufficient mass. In stars [[Asymptotic giant branch|heavy enough]], after the supply of hydrogen is exhausted in their cores, their cores (or a shell around the core) start fusing [[triple-alpha process|helium to carbon]]. In the most massive stars (at least 8–11 [[solar mass]]es), the process is continued until some of their energy is produced by [[Silicon burning process|fusing lighter elements to iron]]. As iron has one of the highest [[binding energy#Nuclear binding energy curve|binding energies]], reactions producing heavier elements are generally [[endothermic]]. Therefore, significant amounts of heavier elements are not formed during stable periods of massive star evolution, but are formed in [[R-process|supernova explosions]]. [[s-process|Some lighter stars]] also form these elements in the outer parts of the stars over long periods of time, by absorbing energy from fusion in the inside of the star, by absorbing neutrons that are emitted from the fusion process.

All of the elements heavier than iron have some potential energy to release, in theory. At the extremely heavy end of element production, these heavier elements can [[exothermic|produce energy]] in the process of being split again back toward the size of iron, in the process of [[nuclear fission]]. Nuclear fission thus releases energy that has been stored, sometimes billions of years before, during stellar [[nucleosynthesis]].

=== Magnetic confinement ===
{{main|Magnetic confinement fusion}}
Electrically charged particles (such as fuel ions) will follow [[magnetic field]] lines (see [[Guiding center#Gyration|Guiding centre]]). The fusion fuel can therefore be trapped using a strong magnetic field. A variety of magnetic configurations exist, including the toroidal geometries of [[tokamak]]s and [[stellarator]]s and open-ended mirror confinement systems.

=== Inertial confinement ===
{{main|Inertial confinement fusion}}
A third confinement principle is to apply a rapid pulse of energy to a large part of the surface of a pellet of fusion fuel, causing it to simultaneously "implode" and heat to very high pressure and temperature. If the fuel is dense enough and hot enough, the fusion reaction rate will be high enough to burn a significant fraction of the fuel before it has dissipated. To achieve these extreme conditions, the initially cold fuel must be explosively compressed. Inertial confinement is used in the [[hydrogen bomb]], where the driver is [[x-rays]] created by a fission bomb. Inertial confinement is also attempted in "controlled" nuclear fusion, where the driver is a [[laser]], [[ion]], or [[electron]] beam, or a [[Z-pinch]]. Another method is to use conventional high [[explosive material]] to compress a fuel to fusion conditions.<ref>F. Winterberg "[https://arxiv.org/abs/0802.3408 Conjectured Metastable Super-Explosives formed under High Pressure for Thermonuclear Ignition] {{Webarchive|url=https://web.archive.org/web/20230303045020/https://arxiv.org/abs/0802.3408 |date=3 March 2023 }}"</ref><ref>Zhang, Fan; Murray, Stephen Burke; Higgins, Andrew (2005) "[http://www.wipo.int/pctdb/images4/PCT-PAGES/2006/102006/06024137/06024137.pdf Super compressed detonation method and device to effect such detonation]{{dead link|date=January 2012}}"</ref> The UTIAS explosive-driven-implosion facility was used to produce stable, centred and focused hemispherical implosions<ref>I.I. Glass and J.C. Poinssot "[https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19700009349_1970009349.pdf IMPLOSION DRIVEN SHOCK TUBE] {{Webarchive|url=https://web.archive.org/web/20230402100741/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19700009349_1970009349.pdf |date=2 April 2023 }}". NASA</ref> to generate [[neutron]]s from D-D reactions. The simplest and most direct method proved to be in a predetonated stoichiometric mixture of [[deuterium]]-[[oxygen]]. The other successful method was using a miniature [[Voitenko compressor]],<ref>D.Sagie and I.I. Glass (1982) "[https://web.archive.org/web/20110522030502/http://handle.dtic.mil/100.2/ADA121652 Explosive-driven hemispherical implosions for generating fusion plasmas]"</ref> where a plane diaphragm was driven by the implosion wave into a secondary small spherical cavity that contained pure [[deuterium]] gas at one atmosphere.<ref>T. Saito, A. K. Kudian and I. I. Glass "[http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADP000254&Location=U2&doc=GetTRDoc.pdf Temperature Measurements Of An Implosion Focus] {{Webarchive|url=https://web.archive.org/web/20120720174842/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADP000254&Location=U2&doc=GetTRDoc.pdf |date=2012-07-20 }}"</ref>

===Electrostatic confinement ===
{{main|Inertial electrostatic confinement}}
There are also [[Inertial electrostatic confinement|electrostatic confinement fusion]] devices. These devices confine [[ion]]s using 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. Also, fusion rates in [[fusor]]s are very low due to competing physical effects, such as energy loss in the form of light radiation.<ref>Ion Flow and Fusion Reactivity, Characterization of a Spherically convergent ion Focus. PhD Thesis, Dr. Timothy A Thorson, Wisconsin-Madison 1996.</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>"Stable, thermal equilibrium, large-amplitude, spherical plasma oscillations in electrostatic confinement devices", DC Barnes and Rick Nebel, PHYSICS OF PLASMAS VOLUME 5, NUMBER 7 JULY 1998</ref> a [[Penning trap]] and the [[polywell]].<ref>Carr, M.; Khachan, J. (2013). "A biased probe analysis of potential well formation in an electron only, low beta Polywell magnetic field". Physics of Plasmas 20 (5): 052504. {{Bibcode|2013PhPl...20e2504C}}. {{doi|10.1063/1.4804279}}</ref> The technology is relatively immature, however, and many scientific and engineering questions remain.

The most well known Inertial electrostatic confinement approach is the [[fusor]]. Starting in 1999, a number of amateurs have been able to do amateur fusion using these homemade devices.<ref>{{cite web |url=http://www.fusor.net/board/ |title=Fusor Forums • Index page |publisher=Fusor.net |access-date=24 August 2014 |archive-date=8 August 2014 |archive-url=https://web.archive.org/web/20140808074102/http://www.fusor.net/board/ |url-status=live }}</ref><ref>{{cite web |url=http://www.clhsonline.net/sciblog/index.php/2012/03/build-a-nuclear-fusion-reactor-no-problem/ |title=Build a Nuclear Fusion Reactor? No Problem |publisher=Clhsonline.net |date=23 March 2012 |access-date=24 August 2014 |url-status=dead |archive-url=https://web.archive.org/web/20141030210524/http://www.clhsonline.net/sciblog/index.php/2012/03/build-a-nuclear-fusion-reactor-no-problem/ |archive-date=30 October 2014 }}</ref><ref>{{cite news|url=https://www.bbc.co.uk/news/10385853|title=Extreme DIY: Building a homemade nuclear reactor in NYC|access-date=30 October 2014|date=23 June 2010|last1=Danzico|first1=Matthew|archive-date=16 May 2018|archive-url=https://web.archive.org/web/20180516133915/http://www.bbc.co.uk/news/10385853|url-status=live}}</ref><ref>{{cite web |last=Schechner |first=Sam |url=https://online.wsj.com/news/articles/SB121901740078248225 |title=Nuclear Ambitions: Amateur Scientists Get a Reaction From Fusion |work=The Wall Street Journal |date=18 August 2008 |access-date=24 August 2014 |archive-date=3 March 2014 |archive-url=https://web.archive.org/web/20140303102549/http://online.wsj.com/news/articles/SB121901740078248225 |url-status=live }}</ref> Other IEC devices include: the [[Polywell]], MIX POPS<ref>{{cite journal|bibcode=2005PhRvL..95a5003P|doi=10.1103/PhysRevLett.95.015003|title=Experimental Observation of a Periodically Oscillating Plasma Sphere in a Gridded Inertial Electrostatic Confinement Device|pmid=16090625|journal=Phys Rev Lett|year=2005|volume=95|issue=1|pages=015003|vauthors=Park J, Nebel RA, Stange S, Murali SK|url=https://zenodo.org/record/1233951|access-date=25 August 2020|archive-date=23 October 2020|archive-url=https://web.archive.org/web/20201023003428/https://zenodo.org/record/1233951|url-status=live}}</ref> and Marble concepts.<ref>"The Multiple Ambipolar Recirculating Beam Line Experiment" Poster presentation, 2011 US-Japan IEC conference, Dr. Alex Klein</ref>