D-D fusion is not as bad as you claim, and the feasibility of p-B11 net power reactors is far from a 'given' at this point. There are many factors which might limit the maximum size of the polywell reactor, such as cooling limits, that might allow polywell to work successfully with D-T, D-D, and D-He3, but still leave it impractical with p-B11.JoeStrout wrote:I doubt that. D-D fusion is easier energetically, but if the Polywell approach works at all, then that won't matter much — power scales as the 7th power of the reactor size, so if your reactor can't burn p-B11, you just need to make it a little bigger.jlumartinez wrote:I try to be realistic. Enthusiasm is fine and is a powerful engine for this enterprise. The equilibrium between being enthusiastic and rational is the key point. In my opinion too many people try to see a far future ahead. Although p-b11 may be reachable the first generation of Polywell (if successful- we hope that-) will be with D-D fusion reaction.
And the trouble with D-D is that the fusion products are neutral — in fact they're mostly neutron radiation, which is nasty stuff, and extremely hard to actually extract energy from. This quickly takes you down that rat-hole of lithium blankets, your reactor quickly becoming radioactive as you use it, a thermal cycle with moving parts, and so on. By comparison, p-B11 fusion with a deceleration grid for extracting the energy is much simpler. For this reason, I doubt D-D fusion will ever be used as a power source (though it makes a dandy neutron source).
D-D fusion releases only 1/3rd of its output energy as neutrons - the rest as charged particles. If you can avoid fusing the tritium in the reaction product, and feed the He3 from the reaction back into the polywell, then a full 90% of the fusion energy is released as charged particles. If you can store the tritium you produce until it decays and feed the resulting He3 back into the reactor, then you end up with only 5.5% of the total energy output released as neutrons.
I have actually been contemplating the possibility that the first net-power polywell reactor should burn D-T, and dismiss the neutrons produced from the reaction as waste heat. Even though this means throwing away 80% of the energy from the reaction, it could still be a net win, because the D-T reaction is so easy, and the alphas that will be produced will all be 3.5Mev exactly. Because the reactor would use a very simple grid array to tap the energy from the alpha particles, it could be cheaper per watt of electricity than any steam turbine based powerplant.