[ShinyRice]

A bigger problem in getting power from fusion is dealing with the resulting neutrons. You can't redirect them out the exhaust, so it's energy you've lost (unless you harness the thermal power of the reactor rather than straight up using it for thrust); they bombard the reactor and can cause regular matter to become radioactive...

[pmayrgundter]

I think that's true for the easier to ignite reactions like D-T, but there are others that are aneutronic, eg Proton+Boron. It's much harder to initiate, but the fuel is cheap and the energy output higher.

"Aneutronic fusion loses much of its energy as light... Since X-rays can go through far greater material thickness than electrons, many hundreds or thousands of layers are needed to absorb the X-rays." https://en.m.wikipedia.org/wiki/Aneutronic_fusion

Now the Army research in the OP doesn't go up to XRay frequencies, but I haven't found a hard upper limit to the coupling effect yet.

[infogulch]

What if the fusion container was an x-ray laser? Could it induce fusion, where emitted xrays are in phase with the laser? I can imagine that an extreme high energy, directable, phase aligned, giant laser power source could be pretty useful.

[pmayrgundter]

Yeah, the NIF experiment is laser driven fusion, but I don't think that even being in phase would help capture the light. Not sure. It's the Ryberg coupling with light (without the usual requirement of just lots of mass/shielding) that's kind of unique here