Has any fusion reactor produced usable electricity, if only as a proof of concept?
Which is understandable, since this is the easy part (not very different than the setup in a fission or coal plant), and there's absolutely no reason to do so until we have seen ignition.
With the millions of degrees being involved, seems a little more than "not very different" than a fission reactor. But would like to hear how this is supposed to work.
But one end product of the fusion process is neutrons. Neutrons are unaffected by the magnetic confinement, they pass right through and hit the jacket of the reactor, where they are absorbed. This heats up the material, which is why you can run cooling water through the jacket which turns into steam. This steam spins a turbine.
There's some engineering challenges (neutron bombardment turns steel and concrete brittle, and later radioactive), but in the end its very similar to a normal fission reactor.