Studies on the breakdown and sustainment of hollow cathode discharges

Two types of hollow cathode discharges in helium have been observed in experiments with a cylindrical hollow cathode: A low current discharge (<1A) at low pressures and high voltages and a high current discharge (>100 A) at higher pressures and lower applied voltages. It is suggested, from these experimental results that the two types of discharges represent two temporal stages of the hollow cathode discharge at one given pressure. In modeling the breakdown of the hollow cathode discharge, it is assumed that a predischarge is initiated by the Paschen breakdown mechanism. Hollow cathode discharges operate to the lower pd branch (where p is the pressure and d the electrode spacing), of the Paschen curve. Thus the breakdown into the low current mode, the predischarge, occurs over the longest possible distance between the anode and the cathode. which is the path from the center of the plane anode to the bottom of the cathode hole