2.13 Behaviour of ceramic insulator materials during initiation of trigger discharge in TVG

Abstract

An effort has been made by the author to design a simple triggered vacuum gap (TVG) in which a plasma discharge over the surface of a ceramic insulator initiates an arc in high vacuum ( p ≤ 10 −5 torr). This design is reported elsewhere. A comprehensive study on the performance of different insulator materials is not reported so far. Thermally stable insulator materials like barium titanate (LCC HTD), silicon carbide, lead titanate, rutile, supramica, alumina, sillimanite and fused quartz in the order of decreasing permittivities, were investigated. The plasma discharge is triggered with a positive voltage pulse to the trigger electrode under low voltage conditions ≤220 V, 100 A for the main electrodes. Samples like barium titanate, rutile, sillimanite showed very consistent performance even up to 1000 trials indicating that a low voltage switching device operating in high vacuum is feasible. During these experimental investigations, both external triggering and self triggering modes have been tried, the latter successfully solving the arc-initiation problem in a much simpler way. This paper presents the results obtained with the above samples at 1–5 × 10 −6 torr.