XPS/SEM Investigation of Electrode Erosion Phenomena in a High Voltage Gas Switch

Abstract : Nowadays triggered spark gap switches are commonly used in many pulsed power systems in order to obtain low jitter in high voltage and high current applications. However, performances and lifetime of this kind of switches may be reduced due to electrodes erosion phenomenon. It may be a barrier when the spark gap switch is used to synchronize several transient pulses. The paper deals with a study of this phenomenon on the main spark gap switch used in a 40 kV/6.25 Ω Blumlein generator. The spark gap switch is composed of 25 mm spherical electrodes triggered by a profiled ring. In these experimental conditions, electrodes are submitted to a pulse of 14 kA during 1 μs. The energy delivered is too high to ensure a sufficient lifetime for our application (100,000 shots expected). The erosion characteristics of four different electrode materials (graphite, copper, stainless steel, tungsten and cuten) are determined. These materials are generally used in air gas switch due to their electrical and mechanical properties (molten rate, rougher and conductivity for example). To evaluate this phenomenon, experimental techniques based on XPS (X-ray Photoelectron Spectroscopy) and SEM (Scanning Electron Microscope) analyses were used. Theses techniques allow characterizing microscopically the surface of electrodes and making a physico-chemical analysis. Investigations consisting in high current tests combined with these physicochemical techniques are presented in the paper. A discussion is proposed to identify the most suitable electrode material for use in high current applications.