Investigation of Arc Motion in Railgun Gas Switch in Oscillatory Regime of Discharge

Abstract

Discharge of a capacitive storage on a load with unipolar pulse is employed for pumping of powerful lasers and also for feeding of electromagnetic launchers, and pulsed high magnetic field facilities. Spark gaps are often used to commute energy on a load. Triggered spark gaps with electrodynamical acceleration of spark channel were developed and investigated by Kovalchuk and colleagues for the unipolar pulse mode. In some applications oscillatory regime (underdamped sinusoidal) has to be realized for the capacitor bank discharge. In particular, it is valid for a pulsed electromagnetic forming (EMF) technology, which is used for assembling welding, cutting, and forming the details of products in various branches of industry. Spark gaps, developed for unipolar discharge, cannot directly be employed in under-damped (oscillatory) regime, because at current transition through zero the arc channel could stop motion and ignite at initial place on the following half period. Process of the arc ignition and motion became more complicated in the oscillatory regime of capacitor bank discharge. Compact gas switch, intended for operation in oscillatory (low damping) regime of discharge, was introduced later. It is two-electrode switch with electrodynamic acceleration of a spark channel and a matched series injection trigger generator. Two operations regimes have been investigated, namely “fast” regime with current amplitude ~ 160 KA, total charge~ 12 C, period of oscillations 60 µS, full pulse length ~ 400 µs and “slow” regime with current amplitude ~ 30 KA, total charge 18 C, period of oscillations 360 µS, full pulse length ~ 3 ms. The spark gap is designed for 50 kV charging voltage, at a current up to 200 kA, and up to 20 C charge transfer. Two main objectives were pursued in this work: 1. develop test bed for investigation of the spark channel motion for the oscillatory regime of capacitor bank discharge; 2. Investigate arc motion depending on the current and charge transfer in wide operation range and compare it with simulations. In this report we present the test bed schematics and results of the tests.