Four-Framing Camera with Nanosecond Resolution for Flashover Process Diagnostics

Vacuum surface flashover along solid insulator remains a major cause of high voltage device failure, therefore attracts sustainted research interest during the past a few decades. Current investigations of flashover encounter a bottleneck period due to incomplete understanding of the underlying physical mechanism. Optical diagnostics for evolution of surface flashover process can provide a new insight to its mechanism. However, the surface flashover process is a nanosecond (ns) scale transient phenomenon, and most of the existing diagnostic cameras are unable to obtain two-dimensional images with such high temporal resolution. In this paper, a four-framing camera with subnanosecond temporal-resolution was developed and tested. By adopting avalanche transistor switches in the subnanosecond gating module for photocathode in the image intensifier, a minimum gate width of ~1ns of each frame was achieved. The spatial resolution of the camera can reach 35 lp/mm. A combination of analog and digital circuit was designed to realize a large delay range from picosecond (ps) to millisecond (ms), with a high accuracy of 150 ps within 10 ns range, therefore the time interval between consecutive frames can be adjusted flexibly according to different applications. The developed camera successfully captured the fast-evolving surface discharge processes, providing a powerful diagnostic tool for fundamental flashover mechanism research.