A Test Facility for PCSS Triggered Pulsed Power Switches

Abstract

Cost and complexity of pulsed power systems continue to increase as researchers strive for more precise control and flexibility. Systems with large numbers of switches or large numbers of switch trigger times result in the need for more cost effective high performance triggering systems. These needs can be addressed by photoconductive semiconductor switches (PCSS) that have demonstrated 300 ps jitter triggering of 300kV switches. This previous work has motivated continued research into the trigger system parameters that allow for reliable cost effect operation'.To support this research a test-bed has been developed to allow PCSS trigger testing with a variety of high voltage switches (HVS) and switch configurations. The multiple subsystems used in this test bed include: (1) the laser diode array (LDA) driver circuit, (2) the PCSS trigger circuit, and (3) the circuit that is switched by the HVS. Items of particular interest are: (1) the benefits and issues with pulse charging vs. DC charging the PCSS trigger system, (2) fiber coupled versus multi-filament laser diode PCSS triggering, (3) high bandwidth diagnostics to measure and determine the impact of sub-nanosecond rise time and jitter triggers for the HVS, and (4) the PCSS trigger circuits required to determine minimum voltage, current, and pulse width for optimal HVS triggering. Our testbed consists of a single module ("brick"), from a linear transformer driver (LTD)2 experiment, housing two 40 nF capacitors, the HVS being tested, and a load. A low inductance HVS that can handle +/-100 kVDC and 5OkA are being tested with this system. The laser diode array (LDA) that triggers the PCSS can be located with the PCSS and the HVS or in the screen room. The LDA is driven by a low energy avalanche trigger circuit that can be optically triggered and floated to HVS. This paper describes the requirements, methods, and the apparatus developed to determine the PCSS minimum electrooptical requirements for optimal HVS triggering. Specific current and voltage waveforms obtained from the sub-systems will be discussed along with the parameters adjusted to deliver a range of pulse widths, rise times, and energies to the HVS.