I don't know how this one in particular is planning to do it, but the Polywell wiffle-ball design uses magnet coolant as a heat transfer medium. I'm sure I've

I don't know how this one in particular is planning to do it, but the Polywell wiffle-ball design uses magnet coolant as a heat transfer medium. I'm sure I've heard of a design that uses charged particles spat out of the fusion reaction directly as charge carriers, too.