I. Introduction
The insulator materials are usually used in the pulsed power systems and high-voltage devices to withstand high-pulsed voltage. The configuration of the insulator stack was utilized in -pinch pulsed power facilities, such as [1], [2], and Julong-1(PTS) [3], [4]. The insulator stack would transmit very high current (MA) to the load and withstand megavoltage. Since the vacuum surface flashover is a typical fault in pulsed power system [5], the insulator performance is required to be enough high to avoid flashover and increase the reliability of the whole system.