Electrode conditioning characteristics in vacuum under impulse voltage application in non-uniform electric field

In this paper, we quantitatively investigated the impulse conditioning mechanism under non-uniform electric field electrodes in a vacuum. A negative standard lightning impulse voltage was applied between rod and plane electrodes whose materials were Cu-Cr, stainless steel and Cu and the gap lengths were d = 5 and 10 mm, respectively. Experimental results revealed the transition of the breakdown (BD) spot region on the rod electrode and the corresponding BD field strength in the conditioning process. As a result, we found that the BD spot region started at the tip of the rod electrode and moved to the wider region of the rod electrode with lower electric field as the shots of the voltage application increased before the saturation of the BD voltage. Finally, by analyzing the results with an electric field strength, we propose that "the conditioning degree" along the electrode surface distributed directly proportional to the electric field distribution under a non-uniform electric field in a vacuum, irrespective of the electrode materials.