Spectral analysis of breakdown at or near RF windows

The University of New Mexico (UNM) klystron test stand can generate microwave pulses up to 2-ms long with a frequency of 850 MHz and a peak power of 1.26 MW. For these experiments, the klystron output was used to simulate field breakdown near or on the surface of RF vacuum windows. RF-driven discharges were initiated in vacuum waveguide sections between copper electrodes. Data were gathered for discharges in the gap between the electrodes and for discharges between the electrodes and across the surface of the ceramic alumina. The generated optical signals were captured through three different windows (sapphire, crystal quartz, and NaCl) using different photo-multiplier tubes (PMTs). Issues addressed include a partial analysis of the spectra from metal/metal and metal/ceramic arcs and an investigation of arc precursor emission. The results of these preliminary tests will be used to optimize selection of optical components in an arc detection systems.