Matt M wrote: I understand that the current plasma is being ‘poisoned’ by small amounts of copper and silver. But – won’t the tungsten cathode contribute tungsten impurities to the plasma?
Tungsten is much harder than copper or silver and has a much higher heat of vaporization than either of those metals.
heat of vaporization:
silver: 250.58 kJ·mol−1
copper: 300.4 kJ·mol−1
tungsten: 806.7 kJ·mol−1
Interesting to note that there’s no reading for tungsten in that chart… and there’s a ring of tungsten with “teeth” at the base of the anode.
