Design criteria for low-scattering and long-lifetime gas-insulated self-breakdown spark gaps

Abstract

Summary form only given: Industrial applications of pulsed power require long lifetime switching elements (>109 shots), which are cheap, reliable and simple in construction. Although solid state switching has made considerable progress during the last years, due to economic reasons it cannot replace gas insulated spark-gaps in the switching voltage range of 50 kV and higher. Our fundamental work on gas-insulated spark gaps is based on the volume time law which was stated by Boeck in 1975: dNe(t)/dt=n dot0(t)ldrg(E)ldrdV. The number of seed electrons Ne per time unit which initiate a streamer in the gap and finally lead to a current carrying channel depends on the seed electron generation rate n dot0 and a field dependent weighting function g(E). A low scattering of the breakdown voltage of a pulse charged gap can be obtained, when the probability g(E)dV for channel formation from a seed electron is high and uniform all over the gap volume. Spark gap lifetime mainly is determined by electrode erosion processes. Unequally distributed electrode erosion along the electrode surface changes the field distribution in the gap and consequently the switching performance of the spark gap. This finally limits its maintenance-free lifetime interval. A maximum lifetime can be achieved, when the probability for channel formation is uniform at each electrode surface element. All conditions can be fulfilled by an electrode shape which realizes a uniform field in a large gap volume. Breakdown voltage measurements show, that the RMS-jitter significantly decreases when uniform field electrodes (Borda-profile) are used instead of spherical shaped electrodes. The switching performance further can be improved by using an auxiliary corona discharge which enhances the seed electron generation in the gap.The influence of gap volume, field distribution and seed- electron generation rate on pulse-to-pulse stability of gas insulated self breakdown spark gaps will be demonstrated by measurement results.