Abstract Number #10319 ADVANCED MULTI-GAP PSEUDOSPARK SWITCH ∗ Andras Kuthi, Brian Eccles, Qingfang Yao, Chunqi Jiang, and Martin Gundersen ξ , Department of Electrical Engineering – Electrophysics University of Southern California Los Angeles, CA 90089-0271 Klaus Frank, Physics Dept. I, Univ. Of Erlangen, Erwin Rommel Str. 1 D-91058 Erlangen, Germany ∗ This work was primarily funded by the Compact-Pulsed Power MURI program funded by the Director of Defense Research and Engineering (DDR&E) and managed by the Air Force Office of Scientific Research (AFOSR) and was also funded by the Army Research Office (ARO). ξ email: mgu@usc.edu Abstract The design and initial operation of an advanced multi-gap Pseudospark device is presented. Forced grading of the intermediate electrodes in the switch will be achieved by taps on the charging transformer. Gap synchronization is aided by UV illumination of all gaps from the primary gap trigger. Initial switch operation in triggered and self breakdown modes and the resulting rise times is evaluated. The switch is intended to be the critical part of a 500 kV, 10 kA, 200 ns Transmission Line Transformer based pulse generator. I. INTRODUCTION High power, high repetition rate modulators and pulsed power systems require fast switches capable of operating at high current and high voltage. Transmission Line Transformer based pulse generators relax the voltage hold-off requirements of the main pulsed power switch by about a factor 2 or 3, but for a 500 kV, 10 kA, 200 ns output TLT generator the switch still has to hold off 200 kV [1]. The Pseudospark discharge can be used as a fast, long life, High Voltage (HV) switch [2, 3, 4, 5]. Commercial versions of Pseudospark switches are now available [4]. They compete well with traditional hot cathode type Thyratrons, and just as the Thyratron, they suffer from some limitations. One of the limitations is that the hold- off voltage for a single gap device cannot comfortably exceed 32 kV without impairing the switch lifetime. For applications requiring low current (usually < 2 kA), short (< 200 ns), pulses the switch can be operated in the glow discharge mode as compared with the high current (> 4 kA) superemissive mode, and then the lifetime limit due to electrode erosion is not a serious problem. For a limited number of pulses the breakdown voltage can be increased to ~50 kV, basically limited only by electrode surface induced vacuum breakdown effects. In this mode, the switch lifetime is limited not by significant electrode erosion changing the effective geometry of the main discharge gap, but by impurities and electrode and insulator surface changes leading to loss of voltage hold- off even in vacuum. Attempts to overcome the single gap voltage hold-off limit led to the development of multiple gap structures. An optically triggered version, the so called Back-Lighted Thyratron (BLT), was investigated early and a two gap BLT was found to hold off 70 kV DC, and triggered at ~65 kV, and a three gap BLT has achieved 100 kV hold- off voltage at slightly lower pressure [6]. These experiments used stacked single gap switches, so the switch size was not optimized for the voltage hold-off achieved. The problem of overvolting the upper gaps and thus causing rapid degradation of the electrodes was solved by simultaneously triggering all gaps with the help of optical fibers. These fibers, however, caused impurity release and subsequent rapid deterioration of hold-off voltage. The impurity problem could be reduced by restricting the optical trigger to the cathode and opening up 5 mm diameter holes along the axis through the partitions between the gaps, so the upper gaps could be illuminated by the cathode gap. This Ultraviolet (UV) trigger of the upper gaps eliminated the problem of upper gap overvoltage and erosion. More recent experiments aimed at optimizing a two gap electrically triggered Pseudospark configuration [7, 8]. Frank et.al., reported a doubling of the hold-off voltage at constant pressure using a flat disk middle electrode with a circle of holes displaced from the center, so no reduction