Fission is where the driving energy is coming from but yes, the detail is unimportant. Like Daedalus, it envisioned D-He3.

"pretend we have a pulsed fusion reaction". Well, I guess that's what I'm asking about. I know that in a lab sense making fusion is easy; getting useful energy out sustainably has been the hard part. But what if you don't care about the fusion plasma being self-sustaining and happily let it escape? I envision it buying you exhaust at fusion fuel energy density and particle velocities, which is as good as we can hope for in an interstellar ship, short of antimatter or giant beams.