Measurement of ion flux as a function of background gas pressure in a Hot Refractory Anode Vacuum Arc

The fraction of the ion flux in the radially expanding plasma flux was obtained in hot refractory anode vacuum arc by measuring the ion current and the film deposition characteristics. Experiments were conducted with an arc current of 200 A, a molybdenum anode and an electrode separation of about 10 mm. It was found that the collected ion current in vacuum increased about twice from the beginning of the arc (t < 30 s) to the developed HRAVA stage (t > 50-60 s). The measured ion current in argon, nitrogen, and helium environments remained approximately constant with background gas pressure up to some critical pressure (15, 30, and 75 mTorr for argon, nitrogen and helium respectively), and then decreased with pressure eventually reaching zero. The ion fraction in total deposition flux was 0.6 in vacuum and decreased with nitrogen pressure except for the pressure range 10-100 mTorr where the local maximum about 0.8 was observed