Is There a Better Route to Fusion?

Following presentation adapted from T. H. Rider Ph.D. thesis, MIT
Published with permission June 2015
All rights reserved by original author & institution

“Thirty-five years ago I was an expert precious-metal quartz-miner. There was an outcrop in my neighborhood that assayed $600 a ton—gold. But every fleck of gold in it was shut up tight and fast in an intractable and impersuadable base-metal shell. Acting as a Consensus, I delivered the finality verdict that no human ingenuity would ever be able to set free two dollars’ worth of gold out of a ton of that rock. The fact is, I did not foresee the cyanide process… These sorrows have made me suspicious of Consensuses… I sheer warily off and get behind something, saying to myself, ‘It looks innocent and all right, but no matter, ten to one there’s a cyanide process under that thing somewhere.’”
-Mark Twain, “Dr. Loeb’s Incredible Discovery” (1910)

Wish List of Characteristics For the Perfect Nuclear Energy Source

• Little or no radiation and radioactive waste
• Minimal shielding
• Scalable to power everything from computer chips to GW reactors
• High-efficiency direct conversion to electricity
• Utilizes readily available fuel
• Cannot explode, melt down, or frighten Jane Fonda
• Not directly or indirectly useful to terrorists or unfriendly countries

Can we come closer to meeting these goals?

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Fundamental Constraints on Fusion Approaches

Best foreseeable 1 GWe (3 GWt) magnetic fusion reactors:
• D+T: 2.4 GW of 14-MeV neutrons, 1.6 giga-Curies (GCi) of T stockpile/year
• D+D w/o product burnup: 1 GW 2.5-MeV neutrons, 1 GW X-rays, 70 GCi T
• D+D with product burnup: 1.1 GW mainly 14-MeV neutrons, 180 MW X-rays
• D+3He w/o product burnup: 30 MW 2.5-MeV neutrons, 500 MW X-rays, 1.8 GCi T
• D+3He with product burnup: 150 MW mainly 14-MeV neutrons, 500 MW X-rays
• Mainly thermal (Carnot-limited) conversion of fusion energy to electricity

Potential Thesis (or Nobel Prize) Topics

Fusion reactions
• In the table of possible fusion reactions, should additional reactions be green?
(Consider competing side reactions and idealized breakeven against bremsstrahlung.)
• Are there any promising reactions not in the table (due to higher Z or shorter nuclide half-life)?
Can one provide better evidence (especially experimental) for or against spin polarized fusion?
• Benefits of spin-polarized fusion (especially for D+D reaction enhancement or suppression).
• Methods of producing polarized nuclei.
• Mechanisms and rates of depolarization relative to the fusion rate.

Fusion catalyzed by massive negative particles
• Are there more efficient muon production methods?
• Are there practical methods for unsticking muons from alpha particles?
• Are there methods to reduce the muon catalysis cycle time?
• Are there any massive negative particles that are more suitable than muons for catalysis?
• Can the effective electron mass or charge be increased in useful ways?

Other ways to improve the tunneling factor
• Is there a way to keep scattering from hindering shape-polarized fusion?
• Is the resonant tunneling model valid, and does it have useful consequences?
• Is fusion of light elements in liquid metallic states scientifically valid and practical to achieve?
• Are there other ways to improve the tunneling factor?
• Can one prove we have covered the complete phase space of ideas for improving the
tunneling factor?

Other improvements to σ_fus
• Are there ways to improve the wavefunction cross-sectional area factor in σ_fus?
• Are there ways to improve the Breit-Wigner compound nucleus energy resonance factor in σ_fus?
• Are there any other categories of ways to influence σ_fus?

More Potential Thesis (or Nobel Prize) Topics

Fusion products
• Are there practical ways to influence the reaction channels and products?

Plasma properties
• Are there realistic ways to recirculate power and maintain ions in a monoenergetic or anisotropic state, or two ion species at different temperatures (e.g. hot ³He and cold D or hot p⁺ and cold ¹¹B?
• Are there practical ways to reduce ion-electron energy transfer or recirculate power from the electrons back to the ions?
• Are there ways to reduce/convert radiation power losses, especially bremsstrahlung?

Confinement of particles and energy
• Are there practical lessons we can learn from stellar fusion and use to improve fusion reactors?
• Are there ways to overcome the main practical difficulties with inertial confinement fusion?
• Which existing magnetic confinement approach is best, or can a better one be created?
• Can the conduction losses be reduced to make acoustic confinement practical?
• Can fusion-fission hybrids be made more attractive?
• How is ball lightning confined, and can fusion reactors employ a similar approach?
• Is there any feasible way to create a small black hole?
• Are there any other confinement approaches worthy of investigation?

Direct conversion
• What are the most efficient/compact thermal-to-electric converters?
• What are the best converters for light nuclei—traveling wave converters, etc.?
• Are there practical ways to directly convert the energies of recoil nuclei or other heavy nuclei emitted by solid materials?
• What are the best converters for electrons?
• How feasible and efficient are the neutron energy conversion methods of Perkins et al.?
• How feasible and efficient are the X-ray and g-ray energy conversion methods of Wood et al.?

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