Detached Glow Above a Titanium Hollow Cathode Sputter Source

A simple argon hollow cathode (HC) was investigated as a plasma source and a sputtering source for titanium. The HC consists of a Ti cylinder. There are two different modes of operation: a low-current discharge with the typical pink bluish argon glow and the high-current HC discharge mode. In the latter case, an intensive glow was observed at the upper end of the Ti cathode. Under certain conditions, this glow was observed to float freely between cathode and anode ring.