Transmission line switch design for the investigation of sub-nanosecond electrical breakdown

摘要

Ultrafast plasma closing switches rely on sub-nanosecond electrical breakdown of the insulating gas. Until recently, little information was available on gas breakdown occurring within this timescale, because of the difficulties in designing an experimental system for such a study. Recently published papers have reported on the results of studies carried out using two devices designed specifically for the investigation of fast (sub-nanosecond) electrical breakdown processes. The devices are essentially modified transmission line plasma closing switches, and in this paper we describe their structure and operation. Because electromagnetic wave behaviour plays a significant role in sub-nanosecond switching, especially reflections from impedance mismatches, the design of the devices is based on transmission line concepts, rather than those of lumped parameters. One of the switches has a conical transmission line topology and is designed for the study of fast switch closure at insulating gas pressures less than 0.6 MPa. The second has a hybrid radial transmission line/conical transmission line topology and is designed for the study of fast switch closure at pressures up to 10 MPa. The paper also includes details of the D-dot monitors used to investigate sub-nanosecond processes in the two transmission line plasma devices.