People build these Farnsworth fusion devices in their basement all the time as a hobby- probably part of the reason he got second place. The fusion isn't the interesting part- it's his improvisation of various techniques in the construction.
Here's a website about Farnsworth's fusion reactors, including some directions on constructing your own:
http://fusor.netWas the one at the GE pavilion at the NY World's Fair a bigger version of these things? I think it had some kind of plasma compression feature, and gave a pretty good "BANG", as I recall (scared the crap out of me):
