Partial vacuum breakdown of helium at 20 khz for point to-plane geometry

The next generation of space vehicles is likely to utilize higher voltages than the traditional 28 Vdc for onboard power distribution. Such is already the case for the International Space Station (ISS), which utilizes 120 Vdc. The availability of switching power supplies operating at high switching frequencies makes it important to consider the effects of these higher operating frequencies in the context of corona and gas breakdown in space applications. In general, power devices and systems operating in the space environment are more susceptible to partial discharges, corona, or volume discharge due to the partial vacuum environment. Such phenomena within power system components are considered unacceptable in systems where long lifetime and reliability is necessary. The literature suggests that the dielectric strength of certain gases falls off drastically at frequencies over 100 kHz, which is not theoretically predictable W. Pfeiffer (1991). Although there have been studies on the influence of frequency on gas breakdown over specific frequency ranges, this behavior over the range below 1 MHz is not completely understood. In addition, existing data cannot be extrapolated for miniature systems with smaller electrode gaps operating at very low pressures. Our recent studies confirm that high frequency operation in space could be a major concern when designing space power systems Kalyan Kopisetty et al. (2003), and that the breakdown voltage levels at high frequencies (< 1 MHz) can indeed be lower than the DC breakdown voltage levels, at certain pressures. In this paper we present our studies on the breakdown of helium operating at 20 kHz in partial vacuum, for a point-to-plane electrode configuration. An AC voltage source with adjustable DC off-set was used in the experiments. Preliminary results including voltage and current waveforms, along with the light emission data from the discharges are presented. The data suggests that the breakdown is a relatively short - - event occurring within approximately 5 to 10 microseconds, with a relatively large transient current peak. We observe that once the discharge is initiated, it becomes self-sustaining as long as the applied voltage across the electrodes is not removed. Thus, the light emission from the electrode gap is observed for several cycles, although the voltage and current waveforms indicate this process to be in the microsecond range. It was also observed that the breakdown voltage characteristic exhibits a pattern similar to the typical Paschen curve for DC breakdown in gases