- Aug 2018
- Neural Network of the Universe
Ok, but the crucial information is given right at the beginning:A quote from your link
Plasma is the fourth state of matter.
It can be created by sufficiently energetic particles colliding with the residual gas in an evacuated chamber or in the case you mention gas being generated in the chamber by atoms and ions being (thermally)stripped off the solid parts. Specially fabricated electrodes facilitate this. Thorium is a common doping element for this purpose.
But then there is not a perfect vacuum in the chamber.
Of course electrons will come off first as they are much lighter and so require less thermal energy to achieve the necessary kinetic energy to leave the solid.
"A vacuum arc can arise when the surfaces of metal electrodes in contact with a good vacuum begin to emit electrons either through heating (thermionic emission) or in an electric field that is sufficient to cause field electron emission."
Well, either this or I don't know - magic?