We use this effect (halogen cycle with fluorine) to extend cathode life in high power ion sources. With a high AMU process gas the net movement of cathode metal ions is to the chamber liner walls (made of the same material as the cathode. If we switch to a fluorine containing process gas at the correct operating conditions the direction reverses from the walls to the cathode rebuilding the ionization surface without downtime.IME: cathode poisoning is most often caused by undervolted heaters or standing around for long periods with too little anode current - apparently the normal electron flow sweeps up positive ions that bombard and contaminate the cathode coating.
http://en.wikipedia.org/wiki/Halogen_lamp
http://www.google.com/patents/US5943594
This is for an obsolete directly heated source cathode but the same effect can used on IHC.
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