Mr. Sanns, 51 years old, is part of a small subculture of gearheads, amateur physicists and science-fiction fans who are trying to build fusion reactors in their basements, backyards and home laboratories.

Called fusors and based on a 1960s design first developed by Philo T. Farnsworth, an inventor of television, the reactors are typically small steel spheres with wires and tubes sticking out and a glass window for looking inside. But they won't be powering homes anytime soon -- for now, fusors use far more energy than they produce.