Development of Centimeter-class Vacuum Breakdown Characteristics under Microsecond Pulses

This article presents the results of studies conducted at the Northwest Institute of Nuclear Technology, Xi’an, China, on centimeter-class vacuum breakdown characteristics under microsecond short pulses. First, a formula to calculate the vacuum breakdown field ( ${E}_{b}$ ) dependent on the electrode gap, electrode area, and pulsewidth is given. Then, basic breakdown characteristics in a gap range of about 2–4 cm are explored experimentally. As the applied voltage increases, an aging state exists between the micro-discharge and the first breakdown. The relationship between aging voltage ${U}_{a}$ and micro-discharge and first breakdown is ${U}$ (micro-discharge) $ < {U}_{a} < {U}$ (first breakdown). The effect of the electrode material on ${U}_{a}$ is as follows: ${U}_{a}$ (polyimide-covered TC4) $ < {U}_{a}$ (magnetic core) $ < {U}_{a}$ (stainless steel) $ < {U}_{a}$ (TC4) $ < {U}_{a}$ (LY4), where TC4 and LY4 are the titanium alloy and the aluminum alloy, respectively. It has also been experimentally verified that the smaller the roughness of the electrode, the higher the breakdown voltage and the longer the lifetime. In the end, certain experimental proofs that support the clump theory for the long-gap vacuum breakdown mechanism are summarized. All of the results in this article have practical value for long-gap vacuum insulation design.