Depression of insulator charging in vacuum by partial mechanical processing

Abstract

It has been clarified by researchers that insulators having contact angles, e.g. ± 45 ° with regard to the plane electrodes, is hard to acquire charge when they are exposed to high voltages in vacuum. For example, an insulator in the shape of a truncated frustum is free from charging. However, since such insulator has inevitably large volume, it obstructs the compactness. On the other hand, roughening insulator surface is also effective to prevent the surface from charging. In this case, the cost for roughening the entire surface may be high when the insulator is large. In this paper we review our previous investigation results and describe new experimental results aimed at developing feasible and compact insulators used in vacuum. Surface charging characteristics of partially and mechanically processed insulators have been studied for this purpose. That is, the charging phenomena when such insulators are exposed to a ramped dc or ac voltage have been observed by using a capacitive probe embedded in the cathode. Firstly, we describe of a partially roughened cylindrical insulator, where the height of the roughened surface measured from the cathode is varied keeping the total length constant. Secondly, we describe a cylindrical insulator having a truncated conical frustum or a chamfer at its cathode-side end. Based on these experimental and simulation results we prove that the partial mechanical processing is effective to control and suppress the insulator charging in vacuum.Index Terms = Surface charge, flashover, depression and control of charging, dc and ac high voltages, roughening, truncated conical frustum, partial processing, vacuum.

Experiences in Numerical Analyses of Surface Charge on Insulators Exposed to High Voltage in Vacuum

“…Such united calculation code, together with the reliable characteristics of a secondary electron yield and of a field emission of electrons, will solve the key problems, since the field emission will be stopped when the surface acquires a certain amount of negative charge. The field calculation and the trajectory calculation codes have been already developed [9,16,17], but on the way to the goal.…”