Electrode Material Dependence of Dielectric Strength Improvement in High Frequency AC Conditioning in Vacuum

Spark conditioning by repeated breakdowns (BDs) with AC voltage application is an effective method for improving dielectric strength in vacuum. During AC conditioning, the multiple BDs occur successively in a half cycle of AC voltage application. It is considered that the multiple BDs are harmful for conditioning and triggered due to the previous BD in the same half cycle. In our previous research, we have confirmed that high frequency AC conditioning suppress the multiple BDs and improves dielectric strength for the Cu electrodes. In this paper, we discuss the electrode material dependence of the dielectric strength improvement in high frequency AC conditioning in vacuum. We compare high frequency AC conditioning effect for the stainless steel (SUS) electrodes with that for the Cu electrodes. Experimental results have revealed that the high frequency AC conditioning improved the dielectric strength by 16% for the Cu electrodes, but did not almost improve for the SUS electrodes. It is considered that the harmful effects of the multiple BDs are significant for electrode materials with high electrical and thermal conductivities such as Cu, and the dielectric strength improvement by the suppression of the multiple BDs due to high frequency AC conditioning is expected to be useful for such electrode materials.