There’s a nice tutorial on Makezine.com on how to create your very own Nuclear Fusor. Of course there are some harmful elements to this project and I don’t think you’ll get as much power out of it than you would initially think, but it’s a very cool to show off to your friends. Below is a brief description of it’s operation.
The typical Farnsworth-Hirsch fusor has two concentric electrical grids inside a vacuum chamber: an inner grid charged to a high negative potential, and an outer grid held at ground potential. Our benchtop version has a stainless steel wire inner grid, and uses the aluminum chamber walls as the outer grid.
A variac controls the AC mains voltage input to a neon sign transformer, which steps up standard 110V AC to the 10kV range. A homemade rectifier converts AC to DC power to charge the grid.
A vacuum pump evacuates the chamber to a pressure of about 0.025mm of mercury, clearing the playing field so the few remaining gas molecules can accelerate without premature low-energy collisions. A vacuum gauge indicates the pressure inside.
High voltage across the grids causes gas molecules to ionize; that is, they lose an electron and become positively charged. Electrostatic forces then accelerate the ions — mainly O2+, N2+, Ar+, and H2O+ — toward the high negative charge at the center. Some ions collide; those that miss the first time are arrested by the electric field and re-accelerated toward the center for another go.