Philo T. Farnsworth famously invented a fusor in 1964: https://en.wikipedia.org/wiki/Fusor https://en.wikipedia.org/wiki/Fusor He was an inventor of a variety

Philo T. Farnsworth famously invented a fusor in 1964: https://en.wikipedia.org/wiki/Fusor https://en.wikipedia.org/wiki/Fusor He was an inventor of a variety of television technology, and I believe the designs were very similar to his fusor. Unfortunately, the design cannot be made "exothermic" IIRC, and the research ruined him financially.