Nanosecond-frame imaging of plasma discharge in a microwave pulse compressor interference switch

Abstract

The evolution of the light emission from the plasma, which is formed to release the microwave energy from the S-band pulse compressor, was studied using fast-frame (2 ns) optical imaging with a 4QuikE intensified camera. The compressor comprised a cavity filled with pressurized air at up to 3·105 Pa pressure and an H-plane waveguide tee as an interference switch; it generated output pulses of ∼8 ns duration and up to 7.4 MW peak power in 2.766 GHz frequency. The plasma discharge in the switch was triggered by a Surelite laser. From the imaging data, the typical size of the plasma and the velocity of its expansion along the RF electric field were determined and the plasma density was estimated. The influence of the plasma time- and space evolution on the power and waveform of microwave output pulses observed in the experiments was determined in numerical simulations. Simulations showed a good agreement with measurement results in terms of output pulse rise time and efficiency of the microwave power extraction.