There is an active community of amateur open source hobbyists researchers, several of whom have gotten fusors up & running & pumping out neutrons. I don't know how big or powerful the largest ones are, but I don't think anyone's found any hard theoretical limits so far.
Getting one to break even on fusion is at this point a materials problem if I remember correctly. The electrodes start eroding rather quickly when you get to a very high energy level. Looks like one would be quite stunning to see in operation.