Fast-Framing Optical Imaging of Plasma Formation in Resonant Microwave Pulse Compressor

Plasma evolution in the interference switch of an S-band pulse compressor operating in the frequency of 2.766 GHz, with input pulses of 200-450-kW power and duration of 2.4 μs, was studied experimentally and in numerical simulations. The system was filled with dry air at 2 × 105-3 × 105-Pa pressure. The plasma discharge that switches the phases of the compressor operation from energy storage to release was initiated by a Surelite laser. The evolution of the light emission from the plasma was studied using fast-framing optical imaging with a 4QuikE camera. From the obtained typical size of the plasma and its velocity of expansion along the electric field, the density of the plasma was estimated, and the influence of its evolution on the power and waveform of microwave output pulses observed in the experiments was determined in simulations.