The Pump

For a fusor to work you need a vacuum. Having too much air in the chamber where the reaction will happen will slow the ions down and cause no reaction. This is why a vacuum pump is needed. The pump will suck out most of the air in the chamber allowing the little remaining air to ionize and move freely. The pump you will need must be a vacuum pump. Rotary vane vacuum pumps are the best to go for, this is the one I went for -

 http://www.ebay.co.uk/itm/Industrial-Quality-Professional-Vacuum-Pump-50-l-min-/141067535164?pt=UK_BOI_Medical_Lab_Equipment_Lab_Equipment_ET&hash=item20d847c33c

Im sure there are many other vacuum pumps out there that would also work but generally 1/4 Hp, 3 CMF, single stage rotery vane vacuum pumps are the best to go for.

Next: The Rectifier Circuit