STM-D-0954Paper2011Published and peer-reviewed

Channeling of Fusion Alpha-Particle Power Using Minority Ion Catalysis

Andrey Zhmoginov · Nathaniel Fisch

Abstract and summary · read the original at the source · none found

In one page

When deuterium and tritium fuse, nearly a fifth of the energy leaves as fast helium nuclei — alpha particles — and by default those alphas hand their energy to the electrons, which radiate it away as light. Nathaniel Fisch’s alpha-channeling idea is to intercept it: launch a wave that pulls energy out of the alphas and puts it straight into the fuel ions, so the fuel stays hotter than the electrons and burns better. The catch has always been finding a single wave that can talk to both populations at once, and in mirror machines nobody has found a good one. Andrey Zhmoginov and Fisch propose a middleman. Seed the plasma with a trace of heavy ions — they use neon-22 and neon-21 — tuned so the wave resonates with the alphas and with the neon, but not with the fuel. The neon takes the energy and passes it on by ordinary collisions. Their simulations find the window of wave strength in which this works.

Why it matters hereChapter 9 is about what a confined plasma can be made to do to itself, and this is the cleanest example on the site: a wave that reaches into the population of fusion-born particles, takes their energy before the plasma wastes it, and routes it back into the burn. Chapter 12 gets the payoff, because keeping the fuel ions hotter than the electrons is exactly the condition the harder fuels need.

What it claims

01Alpha particles born in deuterium-tritium fusion reactions carry almost 20 per cent of the released fusion energy, and their default fate is to lose it collisionally to the electrons. Transferring that energy rapidly to the fuel ions instead, with the electrons kept cold, increases the effective fusion reactivity — and the means to do it is the alpha-channeling technique, in which a wave extracts the alpha-particle energy and heats fuel ions simultaneously through resonant interactions.Introduction, first paragraph
Settled physics
02The obstacle to conventional alpha channeling is stated plainly: finding modes able to interact vigorously enough with both alpha particles and fuel ions in a practical device can be challenging, and in mirror machines no such weakly damped modes have yet been identified that would allow transferring most of the energy. Expanding the parameter range within which alpha channeling can be practised is therefore the point of the paper.Introduction, second paragraph, and its note on mirror machines
Published and peer-reviewed
03The proposed mechanism inserts a catalyst. An extracting wave takes energy from the hot alpha particles and gives it to colder injected minority ions, which then forward it to still colder fuel ions through ordinary collisions, so the wave no longer has to interact with alpha particles and fuel ions simultaneously. The minority species must satisfy a double cyclotron resonance, an integer multiple of its gyrofrequency matching an integer multiple of the alpha gyrofrequency, while avoiding resonance with the fuel — and for a 10 kilo-electronvolt plasma the wave frequency must sit within about 5 per cent of the alpha gyrofrequency, which rules out any minority ion lighter than oxygen.Wave interaction with minority species; Equation 1 and Equation 3
Designed, not yet built
04The wave intensity is bounded on both sides. Above the upper bound the minority ions are overheated past roughly a million electronvolts and start heating electrons instead of fuel, which can be avoided by injecting them where the wave is evanescent or by detuning the wave from exact resonance; below the lower bound, if the minority injection energy is under the majority ion thermal energy, the background plasma rather than the wave dominates the heating. The technique is practical only when the intensity needed to extract the alphas falls inside that window.Regimes for the catalytic effect
Designed, not yet built
05For a worked mirror case — mirror ratio 5, electron density 3 times ten to the thirteenth per cubic centimetre, 90 per cent deuterium and 10 per cent tritium, all species at 10 kilo-electronvolts, fully ionised neon-22 and neon-21 injected at 1.1 kilo-electronvolts with a loss boundary at 300 electronvolts and an optimised field near 0.9 tesla — the window is open. With the neon-22 polarisation the intensity needed to extract the alphas within half a collisional slowing-down time is 0.43 of the overheating limit and nearly three times the lower bound, so the alpha-channeling wave is not expected to cause minority-ion overheating.Minority-ion heating and heating of fuel ions; Figure 1a and 1b
Published and peer-reviewed
06Energy carried away by minority ions escaping through the ends of the mirror can be made several times smaller than the energy they mediate, by raising the wave amplitude: the ratio reaches about 5.5 at twice the extraction intensity for one polarisation and about 3.5 for the other. The authors close by naming where the same catalysis should carry: it may also catalyse alpha channeling in rotating plasma, and similar catalytic techniques should facilitate alpha channeling in tokamaks, with different operating modes in toroidal geometry — noting that a successful implementation may require external wave control to hold the mode near its optimum.Energy loss with escaping particles; Conclusions
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Read it · abstract

Abstract

Maintaining fuel ions hotter than electrons would greatly facilitate controlled nuclear fusion. The parameter range for achieving this temperature disparity is shown here to be enhanced by catalyzing the α-channeling effect (wave-induced simultaneous expulsion and cooling of α particles) through minority-ion heating. Specifically, a wave can extract energy from hot α particles and transfer it to colder minority ions, which act as a catalyst, eventually forwarding the energy to still colder fuel ions through collisions. In comparison with the traditional α-channeling mechanism, the requirements are thereby relaxed on the waves that accomplish the α channeling, which no longer have to interact simultaneously with α particles and fuel ions. Numerical simulations illustrate how the new scheme may increase, for example, the effective fusion reactivity of mirror-confined plasmas.

The way in

https://doi.org/10.1103/physrevlett.107.175001TEXT. The full five-page Letter was read for this sheet and every claim below is located against it by section, equation and figure number. It was fetched from the American Physical Society’s own harvest service, harvest.aps.org/v2/journals/articles/10.1103/physrevlett.107.175001/fulltext, which returns the article PDF; the bare record endpoint without the fulltext suffix answers 401. RIGHTS. The Letter carries the line ‘© 2011 American Physical Society’ on its first page and no Creative Commons statement, so only the published abstract is reproduced here. The work was supported by Department of Energy contracts DE-FG02-06ER54851 and DE-AC02-09CH11466, and the Office of Scientific and Technical Information holds it as record 1100975, but a society-published Letter written under a Department of Energy grant is not itself a government document, and no author manuscript was found in an open repository. NAMES. The publisher record gives the authors as A. I. Zhmoginov and N. J. Fisch, both of the Department of Astrophysical Sciences, Princeton University; the given names are Andrey and Nathaniel, and Nathaniel Fisch is the author of the original alpha-channeling proposal this Letter extends. On this site, the same Fisch group’s argument for aneutronic fuel in a dense plasma is at [/library/stm-9aa4e6f741](/library/stm-9aa4e6f741), the experiment that observed ion acceleration by a beam-driven wave in a magnetic fusion device is at [/library/stm-5bd599dfca](/library/stm-5bd599dfca), the first proton-boron-11 measurement in a magnetically confined plasma is at [/library/stm-9e2a22de0f](/library/stm-9e2a22de0f), and a related mirror-and-stellarator power cycle is at [/library/stm-6625a82f89](/library/stm-6625a82f89).

How to cite it

Andrey Zhmoginov, Nathaniel Fisch (2011) Channeling of Fusion Alpha-Particle Power Using Minority Ion Catalysis. doi:10.1103/physrevlett.107.175001

Where it sits in the curriculum

Plasmoids, charge clusters and the orbs Lattice confinement fusion