THE BOTTLENECK IN PSEUDOSPARK DISCHARGES

Physical mechanisms during early phases of pseudospark discharges are still under discussion. Experiments at low rates of current rise (dI/d t < 10(9) A/s) were performed to investigate these phenomena, using fi ltered fast shutter photography of the discharge plasma in the visible wavelength region. Additionally temporally resolved measurements of l ine emission of the filling gas (hydrogen and helium) and cathode mate rial (copper) were performed. These experiments revealed a discharge p hase where the cathode surface involved in the discharge is restricted mainly to the inside of the cathode aperture. The voltage drop during that phase is about 200-400 V and the current density exceeds 1 kA/cm (2). A possible explanation of the discharge mechanisms during that di scharge phase is self-sputtering of cathode material from the cathode surface inside the cathode aperture. The described mechanisms might be fundamental for the transition from the transient hollow cathode phas e to the high current phase in pseudospark discharges. (C) 1996 Americ an Institute of Physics.