Snapshots of nanosecond HPM plasma discharge in waveguides

High-gradient electric breakdown is the limiting factor of high power microwave transmission. By using the four-frame high speed camera, the temporal and spatial evolution of optical emission in different waveguide position is diagnosed in nanosecond time-range. The optical distribution is non-uniform in angular direction, and brighter close to the wall surface than the central space. The light may come from the low energy photons from the continuous bremsstrahlung radiation spectrum by high-energy electron bombarding the metal surface of collector. The multiple reflections of photons in the waveguide lead to the spatial non-uniform illumination.