Nanosecond Snapshots of High-Power Microwave Discharge in Waveguides

Using the same bend waveguide with two different E-field polarization directions, the breakdown phenomena in a curved waveguide with different power capacities were studied. For the case of lower power capacity, breakdown happens at the curved arm; with increasing incident power, the reflected peak amplitude increases, the breakdown delay time becomes shorter, and the reflected pulse gradually overlaps with the incident one, forming a slower falling edge at the end of incident pulse. For the case of higher power capacity, discharge may occur at the connected flanges without the choke shot. Using the four-frame intensified-charged-coupled device diagnosing the nanosecond light emission in each of the vertical and horizontal polarization cases, the intensities in both of the surface layer and the space beyond were found to first become bright during the microwave pulse, and then get dark after the pulse. The multiple bright spots on the wall illustrate the nonuniform plasma development and local high-density plasma at the microprotrusions with field enhancement, triggering the intense high-field emission or explosive emission.