Enhanced conduction time of the plasma opening switches using gas injection and plasma guns coupling

Abstract

The most commonly used plasma guns for the plasma opening switches (POS) in inductive storage devices are the carbon ion injectors, such as the 'flashboard', the operation of which is based on surface breakdown and supplies a high-velocity and moderate density carbon plasma. A simple and compact new plasma source for the POS is presented. According to theoretical studies based on magnetohydrodynamics (MHD), the microsecond-conduction-time plasma opening switch (POS) operation is associated with the thrust of the magnetic field, acting as a piston on the POS plasma. This snowplow effect is predominant in high current level generators, and it is shown that the electrical charge Q, conducted by the POS during the conduction time, must verify Q/spl sim//spl radic/(n/sub c/), where n/sub c/ is the electron density. Two main physical conclusions arise from a simple analysis of the MHD model. Firstly, the creation of a POS plasma with a high velocity is unnecessary, and secondly it is the initial density profile which is determinant to realize a sufficiently long conduction time. According to these considerations, a new method of plasmas creation has been studied and developed. That method consists to inject a gas puff in the POS gap before plasma guns firing. In such a way, the high density conductive fluid, created in the POS, is able to short-circuit the current issued from the generator during the required time. Recent inductive storage experiments at CESTA have shown the possibility of considerable enhancement of the switch conduction time. On the 500 kA and 1 MA generators at CESTA (SINAPS-500 and SINAPS-1000, respectively), conduction times reaching 1.6 /spl mu/s for the MA current level have been performed.