Fusor parts

A fusor really does not have a lot of parts.
Here is a shell  (top of spherical anode is removed for the photo) and the cathode is visible within.  These shown here are not working parts, but they do serve as a way to visualize the two electrodes in relation to each other.

Cathode #1

Most successful of the cathode designs.

Cathode #2

Like #1

Cathode

The formation of the poissor could be manipulated with the design of the cathode, and it was redesigned and tested countless times. Resistant to engineering, it required intuition, vision and imperical testing to build insights and new designs

 

Here is a fusor with ion guns mounted around the spherical anode.  The cathode has windows which correlate to the placement of the guns on the anode.  
 
   
A fusor can be pretty much described as an anode, cathode and ion guns, all the rest of the working parts form inside the cathode and are referred to as "virtual" elements, or electrodes.  That space within is called the "poissor" as Phil named it.