So if the neutrons are untouched by magnetic fields, don't they also heat the magnets? I can see them passing through walls to boil water, but any heat created in the magnets would be very difficult to harvest given the temperatures involved. How much energy would it take to keep the magnets cool in the presence of a sustained (ie days) fusion reaction nearby? Generating such a flux in a bottle surrounded by things that need to be kept so cool sounds a bit of a fool's errand... but I really want practical fusion to be a thing.