The theory

A demo fusor requires a few basic parts:

1. Vacuum system
2. High voltage
3. Chamber

The Vacuum system

A vacuum must be used to remove most of the air inside the chamber. The remaining air particles are ionized by the demo fusor system. Vacuum systems tend to become expensive so its important to keep your eye out on eBay. There are two main different types of vacuum pumping methods:

1. Mechanical pump
2. Diffusion pump

Mechanical pump

A mechanical pump is also called a roughing pump because it removes most of the air inside of the chamber before the diffusion pump kicks on. A really good mechanical pump can take the pressure down to < 5 microns.

Diffusion pump

A diffusion pump is normally not used in a demo fusor because it can take the pressures down a lot lower and there must be remaining air molecules to ionize. The animation below demonstrates the process of a diffusion pump.
http://www.edwardsvacuum.com/uploadedFiles/Resource/Corporate/About_Us/diffusion_pump.swf

The High voltage system

A very high voltage is needed to attract the air molecules to the grid, usually about -1,000 to -10,000 volts aka. -1kv to -10kv (kilo volt). The grid is at the center of the fusor and is wired to a negatively biased power source. We will get into more details later. 
 

The Chamber 

The vacuum chamber is a vary expensive part of the fusor unless you build your own ( go to http://rtftechnologies.org/physics/fusor-mark3-hemisphere.htm for more info), in which case it is still very expensive but not the same as a manufactured one. They are usually made of stainless steel 304 although some demo fusors can be made out of bell jars. They must be vacuum tight.
 


















-Not my fusor-