My vote for best fusion device in fiction goes to the thermocuclear device in “The Fourth Bear:  A Nursery Crime” by Jasper Fforde.  WARNING!  SPOILERS!  MAJOR PLOT POINT REVEALED!  From the book:

...there is a theory that might explain the sort of damage we saw at Obscurity and on the Nullarbor.  It was first postulated in the 1950s but was so far-fetched that even the hard-core pseudoscience elite dismissed it as nonsense.  It was called Cold Ignition Fusion and was a way of building a small thermonuclear device using a deuterium/tritium fuel that could be self-extracting from the heavy hydrogen found in groundwater, and then mass-induced organic trigger to set it off.

Yes.  A thermocuclear device.  Just read the book.  Critical mass at 50kg.

I liked the “fusion reactor overload” in Aliens II, which is probably the thing that got me seriously thinking about fusion back in the ‘80’s, when a physics-major friend of mine explained how hokey that concept was. When I learned that sustained, runaway reactions were impossible with a fusion reactor, it made me wonder why we weren’t putting more resources into its development.