Effect of Initial Electrode Surface and Breakdown Charge on Spark Conditioning in Vacuum under Non-Uniform Electric Field

We discuss the effect of initial cathode surface and breakdown (BD) charge on spark conditioning in a rod-plane electrode system, especially with suppressed BD charge. In the case of Cu rod cathode vs. stainless steel plane anode with a large BD charge, the saturated 50% BD field strength at the cathode tip was independent of the initial cathode surface condition, because the large BD charge led to sufficiently large melting of the cathode surface. However, in the case with suppressed BD charge not enough to remove the large weak points, the saturated BD field strength depended on the initial cathode surface condition. On the other hand, in the case of stainless steel rod cathode vs. stainless steel plane anode, the saturated BD field strength was independent of the initial cathode surface condition. In this case, the anode heating would mainly initiate BD. Since the melting of anode was the starting point of BD, the saturated BD field strength would not depend on the initial cathode surface condition regardless of BD charge.