KaiserJeep - I have not found James Nicoll's opinion to be in the minority as you claim. Indeed, many of the points he brings up are also brought up by the Fusion Technology Institute, ITER association, etc. Perhaps when you say minority you are not referring to scientific voices, but instead the gathering of people posting on a "Lets mine the moon!" forum?
You say D-3He fusion is easier than D+T fusion. This does not appear to be true. Everything I read suggests this fusion cycle should be thought of, at best, a second generation fusion technology. IE, they are saying
after we finally get commercial D+T fusion power up and running, than we can start tackling the
more thorny problems of D-3He fusion. Or to put it more simply, let's learn to walk before we try to run.
This poster explains why D-3He fusion fuel is not more popular than D-T fuel(physics). D-3He needs a factor ~80 above D-T fusion power densities. D-3He burns less easily than D-T fuel, so if faces larger physics obstacles, making it a second generation fuel in many people's minds.
D-3He Fusion - Fusion Technology InstituteA careful study of the conditions required to burn D-3He and D-D fuels in a fusion reactor, with realistic models for bremsstrahling and synchrotron radiation losses, shows that the low reactivity of D-3He and D-D fusion reactions severely restricts the choice of fuel mixtures that can be brought to ignition and requires very low levels of impurities and alpha particle ash, with plasma temperature, density, beta and energy confinement time that are far beyond the capability of any known magnetic confinement system. The fuel mixtures of D-3He and D-D that can be brought to ignition produce large fluxes of neutrons and there are serious problems with fuel cycles and reserves.
FUEL REQUIREMENTS AND RESOURCES
A network of D-3He fusion power stations with the capacity to generate 108 TJ(e) per year (thus 10% of 2100 world energy) would consume about 500 tonnes of 3He per year. There is no significant terrestrial reserve of 3He –– the only prospects are lunar mining or manufacture via the D-D reaction. The Moon’s surface has accumulated 3He by exposure to the solar wind but the concentration of 3He in the lunar surface is so low that a tonne of lunar rock contains less energy than a tonne of coal. Fusion based on lunar 3He would require the mining of 6x1010 tonnes (60,000 million tonnes) of lunar rock each year to supply 108 TJ per year — roughly 20 times present-day worldwide coal production –– and an order of magnitude more would be required for fusion to supply all the world’s energy in 2100. Such an enterprise would be enormously expensive and, with the difficulty of burning the fuel, it is difficult to see that this route would be competitive ecomonically.
CONCLUSIONS
Burning mixtures of D and 3He fuels in a fusion reactor would be extremely difficult requiring much higher plasma temperature, density, beta and energy confinement time than a comparable D-T reactor. This fuel mixture is sensitive to impurities and helium ash, with an upper limit on impurities typically half of that assumed for ITER with D-T.
One of the main attractions held out for D-3He has been the prospect of no neutrons, but the so-called D-lean fuel mixtures that have been advocated to reduce the number of neutrons cannot reach ignition due to the effects of fuel dilution and bremmsstrahlung loss. The optimum fuel mixture (30% 3He: 70% D) would produce substantial numbers of 14 and 2.4 MeV neutrons. The 14 MeV neutrons can be avoided only by T extraction cycles but this brings the extra complexity and risks of storing large quantities of T storage until it decays into 3He. The fully catalised D-D reaction offers no appreciable reduction in neutrons compared to D-T.
Even if all the problems with D-3He can be overcome, the barrier would be the lack of a credible and sustainable source of 3He fuel. Perhaps one day far into the future these fuels will be brought to yield their potential, but the difficulties are so great and the benefits seem to be so marginal that, at the present time, these D-3He and D-D fuels cannot be thought of as alternatives to D-T.
ITER AND FUSION REACTOR ASPECTS THE FEASIBILITY OF USING D-3HE AND D-D FUSION FUELSWhen you have limited resources, both technological and financial, it makes sense to divert these resources into areas that have the most promising cost/benefit ratio. The costs associated with commercial D-3He fusion are literally astronomical. The benefits over D+T fusion are marginal, at best. Therefore it does not make sense to put eggs in this basket at this time. Perhaps many decades from now the picture for D-3He fusion would be more favorable. But at this time, our R&D efforts would be better spent getting D+T fusion working, improving fission, improving fossil fuel efficiency, reducing the cost of renewables, etc.
The oil barrel is half-full.