Editing Fusion power (section)

=== 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=October 9, 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=June 22, 2015|title=Magnetic mirror holds promise for fusion|url=https://arstechnica.com/science/2015/06/magnetic-mirror-holds-promise-for-fusion/|access-date=October 11, 2020|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>