Pulsed series discharges in crossed fields generated in vacuum switches for pressure-measurement application

Abstract

Formative processes of the series crossed-field discharges in vacuum switches were investigated, and pulsed discharges were found feasible for switch-pressure measurement, when solid surfaces within switches are clean. The fact that a vacuum switch is a small, sealed device, causes problems in switch-pressure measurement, to which serious conditions for performance are charged. To solve the problems, pulsed discharges were investigated. The discharge in a switch, identified previously as a series discharge consisting of an inverted magnetron and a magnetron, was generated by rectangular high voltage at amplitude Vd. Discharge currents in formative phases were measured and analyzed. Formative processes were revealed to be composed of triggering and growth. At a large Vd value, the discharges are triggered immediately after the stepped voltage application. Instantaneous discharge triggering assures high reliability in pressure measurement. At small Vd values, times required for triggering are delayed and scattered. In the growth phase, discharge currents proceed to increase in a reproducible pattern, and become saturated. Then they begin to decrease, resulting from pressure decreases due to the pumping effect of discharges. A current increase in the growth phase is always quick, and a decrease after saturation is slow. Magnitudes of the saturation currents are distributed concentratedly. This causes good precision in measurement, typically with errors less than 10% of the measured values. The time intervals necessary to establish the pulsed discharges and the pumping effect to change pressures were analyzed. The measurement range was found to cover a low pressure, down to 1×10−4 Pa, with a pressure decrease of less than 20%, when pumping speed is 4.2 l/s, which is the maximum experimental value. Thus, pulsed series crossed-field discharges were found to be feasible for switch-pressure measurements, when switch interior surfaces are clean.