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Comment by sam | Hacker News Reader

The typical design for a fusion power plant that runs on deuterium tritium fuel is to place a lithium "blanket" around the plasma. 80% of the energy released in the deutrium - tritium fusion reaction comes out in the energy of a neutron which would be absorbed in the blanket, heating it up and also generating tritium fuel which could then be fed back in as half of the fuel (the other half being deuterium which is abundant in seawater).

You would then run a heat exchanger from the hot lithium to create steam to then turn a turbine and make electricity.

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Thanks, that makes a lot of sense.

There is also direct-capture in some fusion designs where the charged by-products are electrically decelerated, producing current. I don't believe this is possible in the standard Tokamak design, but the efficiency gain is a selling point for those designs which do allow it.

That’s right, there are other fusion fuels that have only charged fusion products which could be directly converted to electricity. This is in contrast to deuterium - tritium which releases 80% of its energy in a neutron which has zero charge.

Examples of fusion fuels whose main reaction produces only charged products are deuterium helium-3 and proton boron-11. These reactions however require higher temperatures and better confinement characteristics.

The reason why deuterium tritium is the major focus of most (though certainly not all) research is that it has the highest reactivity at the lowest temperature compared to other fuels. Unfortunately it produces a high energy neutron which makes the conversion to electricity more complex.

Direct capture cannot capture a neutron, as it is not a charged particle. Charged particles are relatively trivial to block with the lithium blanket. Not sure how direct capture could possible be more efficient. Do you have a reference that explains what you are talking about?

You run a fusion reaction that mainly produces charged particles, and then convert the KE of the charged particles directly into electricity. See https://en.wikipedia.org/wiki/Aneutronic_fusion#Energy_captu... .

There's just the matter of getting the temperature up to 10x of an ordinary D-T fusion plasma. Non-equilibrium reactors like the polywell try to bypass the problem entirely, but (to my knowledge) it's very hard to maintain a non-thermal state.

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