Measurement of Discharge Events Due to Voltage Breakdown in High-Voltage Ceramic Feedthroughs

Ceramic insulated hermetic feedthroughs are used as signal and high-voltage conduits for sealed gamma radiation detectors with applications in oil and gas exploration. In configurations where signal and high-voltage are supplied via the same feedthrough, voltage breakdown of the gas filling the gap between the conducting wire and coaxial ceramic insulator may produce a charge pulse that is indistinguishable from a gamma detection pulse. This work describes a method to measure the discrete pulses generated by discharges across an air gap between a conducting wire and a coaxial ceramic insulator at 1600V and 150C ambient temperature. The data presented show results of measurements from discrete discharge events containing between ~0.5 pico-Coulombs and 200 pico-Coulombs of charge per event. Samples were tested that had undergone various operations including welding and soldering. Different cleaning operations were applied to some samples to determine whether discharges could be attributed to surface contamination. Measurements of samples where the ceramic insulator was manufactured using two different forming processes was also performed. This method is shown to provide a sensitive tool to screen hermetic components in radiation detectors used for oil and gas exploration.