Editing Fusion power (section)

=== Triple product: density, temperature, time ===
[[File:Fusion Triples 2021.png|thumb|upright=2|alt=Fusion trapping (left) against temperature (bottom) for various fusion approaches as of 2021, assuming DT fuel. |Fusion trapping (left) against temperature (bottom) for various fusion approaches as of 2021, assuming DT fuel<ref>Wurzel, Samuel E., and Scott C. Hsu. "Progress toward fusion energy breakeven and gain as measured against the Lawson criterion." arXiv preprint arXiv:2105.10954 (2021).</ref> Solid line corresponds to Q = ∞ for IFC (inertial confinement fusion). Dashed line corresponds to Q = 0.01 for IFC. Colored contours correspond to Q factors for MFC (magnetic confinement fusion): Q = ∞ (brown), Q = 10 (red), Q = 2 (yellow), Q = 1 (green), Q = 0.1 (strong blue), Q = 0.01 (lighter blue), Q = 0.001 (even lighter blue), Q = 0.0001 (faint blue).{{clarify|date=March 2025}}]]
The [[Lawson criterion]] argues that a machine holding a thermalized and quasi-[[Neutral particle|neutral]] plasma has to generate enough energy to overcome its energy losses. The amount of energy released in a given volume is a function of the temperature, and thus the reaction rate on a per-particle basis, the density of particles within that volume, and finally the confinement time, the length of time that energy stays within the volume.<ref name="Lawson"/><ref>{{cite web |url=http://www.efda.org/2013/02/triple-product/ |title=Lawson's three criteria |publisher=EFDA |date=February 25, 2013 |access-date=August 24, 2014 |archive-url=https://web.archive.org/web/20140911210243/http://www.efda.org/2013/02/triple-product/ |archive-date=September 11, 2014 |url-status=dead }}</ref> This is known as the "triple product": the plasma density, temperature, and confinement time.<ref>{{cite web |url=http://www.efda.org/glossary/triple-product/ |title=Triple product |publisher=EFDA |date=June 20, 2014 |access-date=August 24, 2014 |archive-url=https://web.archive.org/web/20140911205015/http://www.efda.org/glossary/triple-product/ |archive-date=September 11, 2014 |url-status=dead }}</ref>

In magnetic confinement, the density is low, on the order of a "good vacuum". For instance, in the [[ITER]] device the fuel density is about {{nowrap|1.0 × 10<sup>19</sup> m<sup>−3</sup>}}, which is about one-millionth atmospheric density.<ref>{{cite web |url=https://accelconf.web.cern.ch/e06/TALKS/FRYCPA01_TALK.PDF |title=ITER and the International ITER and the International Scientific Collaboration |first=Stefano |last=Chiocchio}}</ref> This means that the temperature and/or confinement time must increase. Fusion-relevant temperatures have been achieved using a variety of heating methods that were developed in the early 1970s. In modern machines, {{as of|2019|lc=yes}}, the major remaining issue was the confinement time. Plasmas in strong magnetic fields are subject to a number of inherent instabilities, which must be suppressed to reach useful durations. One way to do this is to simply make the reactor volume larger, which reduces the rate of leakage due to [[classical diffusion]]. This is why ITER is so large.

In contrast, inertial confinement systems approach useful triple product values via higher density, and have short confinement intervals. In [[National Ignition Facility|NIF]], the initial frozen hydrogen fuel load has a density less than water that is increased to about 100 times the density of lead. In these conditions, the rate of fusion is so high that the fuel fuses in the microseconds it takes for the heat generated by the reactions to blow the fuel apart. Although NIF is also large, this is a function of its "driver" design, not inherent to the fusion process.