Plasma has been called "the fourth state of matter." It is what happens to a gas when it is energized enough for it's atoms to shed electrons. In this condition a gas is said to be electro-luminescent because it gives off light. Plasma is familiar in every-day life as sunlight, stars, lightning and the auroras. Plasma also forms nebulae and the corona of the sun.

Working with plasma is to recreate what happens in nature on a small scale by controlling a set of conditions very carefully. 
First, one has to isolate a gas that won't break down when it is energized. This is done with the noble gases neon, argon, krypton, and xenon. Helium is difficult to work with and radon has the unfortunate characteristic of being radioactive. Second you need a power supply which can be relatively small if the gas is in a near vacuum. 

Ed Kirshner and Christian Schiess taught a number of plasma classes at the Crucible where I had the privilege to be assistant. It was in these classes that made the jars and developed my ideas for tube & knob bending.