Discharge modes in a hollow cathode geometry

The authors discuss a linear discharge system used to study the pressure dependance of discharges between a plane anode and a hollow cathode. The gas discharges, utilizing a cathode with a cylindrical hole of .48cm in diameter, 1.9cm depth and 2cm spacing between two electrodes, exhibit three distinct modes of operation in He with pressure ranging from 20 mTorr to several Torr. At the mode transitions the current changes over four orders of magnitude in a pressure range of a few mTorr. Electron emission current density from the hollow cathode was found to be homogeneous. In this high impedance mode a filamentary plasma of about 1mm diameter, immersed in a glow, was observed on the axis of the electrodes. This luminous phenomenon is probably caused by a electron beam emanating from the hollow cathode. In this mode of operation the discharge current increased linearly with pressure