Historical research guide · 0351 · 2010

DIRD Aneutronic Fusion Propulsion

DIA / AAWSAP contractor

In one minute

This is the Defense Intelligence Agency’s primer on fusion that makes no neutrons, and on what it would take to fly on it. The organising idea is simple and physical: a neutron carries most of the energy out of the easy fusion reactions, and a neutron is useless to an engineer — it will not turn in a magnetic field, cannot be aimed down a nozzle, and mostly escapes into space with its energy after passing through the crew. Charged particles do the opposite. They stop within a very short distance, give up everything as heat, and can be caught in coils and converted straight into electricity. So the report ranks the reactions that yield only charged particles, finds that proton–lithium-6 and proton–boron-11 score best on John Lawson’s own measure of how hard a reaction is to ignite, and notes that boron-11 is 80 per cent of the boron lying about on Earth. Then it names who is building them, and the three things that still have to be invented.

Connection

This is chapter 12’s fuel choice argued from first principles inside a government document: proton–boron-11 returns three charged alpha particles you can steer and convert directly, not neutrons you must shield against. And it gives chapter 13 the honest ceiling of a reaction drive — the report’s own worked flight to Proxima Centauri spends 85 per cent of the launch mass as fuel to reach 6.5 per cent of light speed — which is exactly why this site treats the vacuum, and not the propellant tank, as the thing to engineer.

From the source

The case for aneutronic fuels is made on where the energy goes. Reactions using isotopes of helium and lithium generate only charged particles, which travel very short distances before giving up all of their energy as heat, so they decrease the need to carry large amounts of shielding; and the energy from those charged particles can be captured in conductive coils and converted directly into electricity by a magnetohydrodynamic generator. Neutrons do none of this — they are difficult to shield, their energy cannot easily be converted to electricity, they cannot be focused into a propulsion beam, and there is a high probability that they escape into space without giving much of their energy to the propellant at all.Introduction, pp. v-vi; Chapter 2, Classic Nuclear Fusion Schemes, p. 13; Chapter 3, p. 18
The reactions are ranked by John Lawson’s 1955 criterion — the triple product of plasma density, energy confinement time and plasma temperature, where lower is better. Deuterium-tritium scores 34; the first aneutronic scheme, deuterium with helium-3, scores 0.43; and the two best performers are proton-lithium-6 at 0.005 and proton-boron-11 at 0.014. The price is ion temperature: 800 and 300 keV respectively, against about 50 keV for deuterium-tritium. Availability favours them too — boron-11 is 80.1 per cent of naturally occurring boron, lithium-6 is 7.5 per cent of all lithium and is mined at Silverpeak, Nevada, while tritium must be manufactured because of its 12.6-year half-life.Chapter 3: Aneutronic Nuclear Fusion Schemes, pp. 18-19
Proton-boron-11 fusion produces three alpha particles and no neutrons, and it has been done. The report states that reliable fusion of a proton with boron-11 was demonstrated in a laboratory setting using a picosecond laser in 2005 by V. S. Belyaev in Russia, at the 300 keV particle energies the reaction requires.Figure 10, p. 19; Appendix B, Fusion Initiation, p. 35
The best developed proposal, in the report’s own judgement, is Robert Bussard’s. His EMC2 Fusion Development Corporation in Santa Fe, funded by DARPA, NASA and the U.S. Navy, builds on the Farnsworth-Hirsch fusor patented in 1968: spherical electrodes drive ions toward the centre of a spherical chamber by Lorentz forces, preheated deuterium with helium-3 or boron-11 is injected into the fusor core, and the resulting heat and particles are collected by an electron beam generator that heats hydrogen propellant for a nozzle. The reported specific impulse of this design is 1,500 to 6,000 seconds, drawing 4.5 to 8 gigawatts from the fusion reactor.Chapter 5, Commercial Development, pp. 22-23; Chapter 7: Conclusions, p. 29; Appendix B, p. 32
Three inventions stand between the idea and the engine, and the report names all three. First, fusion initiation: a reliable, efficient igniter for a reaction needing about 3.3 billion degrees. Second, materials for the ignition chamber and nozzle that survive the temperature and stop both the gamma rays from the fusion products and the bremsstrahlung x-rays thrown off when plasma electrons strike the chamber walls — a parasitic process that cools the plasma and cuts the chance of fusion, and which the report says can be attacked with electromagnets that steer electrons and ions to minimise x-ray production. Third, superconducting magnets capable of 10 tesla, sited close enough to the reactor that gamma heating and embrittlement are design problems in themselves.Chapter 3, bremsstrahlung, p. 19; Appendix B, research challenges, p. 35
The report also states the ceiling of a reaction drive, in its own numbers. An ideal proton-to-helium fusion drive would reach a specific impulse of 0.119 times the speed of light, about 3.6 million seconds; the Bussard aneutronic drive as designed reaches 0.000196, about 6,000 seconds, and considerable work will be needed to approach the theoretical value. Worked out for Proxima Centauri with a 14-tonne drive on a craft the mass of the International Space Station, accelerating at a thousandth of a gravity, the flight takes about 127 years at a peak of 6.5 per cent of light speed — and 85 per cent of the launch mass has to be fuel.Appendix B, pp. 32-35, Table 3 and Figure 15

The way in

https://documents2.theblackvault.com/documents/dia/AAWSAP-DIRDs/DIRD_30-DIRD_Aneutronic_Fusion_Propulsion.pdf

Historical source-access record. This guide links to the original; it does not reproduce the paper text.

Defense Intelligence Reference Document, Defense Futures. DIA-08-1011-003, 01 November 2010 (IcOD: 20 July 2010), produced under the Defense Intelligence Agency Advanced Aerospace Weapon System Applications (AAWSA) Program. Released under FOIA and published by The Black Vault. This is the first of the two aneutronic fusion propulsion reports in the series of 38; the second, filed as DIRD 37 and reaching different conclusions from a systems-engineering rather than a physics direction, is carried on this site as its own document. AUTHOR. Withheld under FOIA exemption (b)(6). The text is written by someone at home in health physics and radiation shielding — sieverts, buildup factors, attenuation coefficients, the Nevada Test Site reactor history — which is recorded here as an inference about the author’s field and not as an attribution. TEXT. The body of the report is reproduced in full below: the introduction, all seven chapters, and Appendix B, the worked aneutronic fusion rocket. Appendix A on relativistic rockets, Appendix C on the antimatter annihilation rocket, Appendix D’s relativistic rocket worksheet, and Appendix E’s endnotes are omitted for length; the complete text is at the source. The document carries a copyright warning against further dissemination of its photographs, so the sixteen figures are not reproduced. The numbered equations were destroyed in the released scan and are stated in words where the surrounding text depends on them; nuclear reactions, isotope notation and exponents are restored from the page images.

How to cite it

DIA / AAWSAP contractor (2010) DIRD Aneutronic Fusion Propulsion https://documents2.theblackvault.com/documents/dia/AAWSAP-DIRDs/DIRD_30-DIRD_Aneutronic_Fusion_Propulsion.pdf

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