The temperature dependence of homogeneous field breakdown in synthetic air

The time-resolved Townsend method is used to measure, among other parameters, the effective coefficient of ionization of α¯/N as a function of E/N in synthetic air (80% N₂ , 20% O₂ by volume) within a temperature range of ~27 to 124°C, where N is the gas number density, and E the electric field strength. Results show that effective ionization coefficients are lower for higher temperatures, thus leading one to infer that breakdown voltages should increase with temperature for constant values of the product Nd, where d is the gap distance. However, systematic breakdown voltage measurements in nearly homogeneous field conditions, did not support this temperature dependence. For room temperature, however, both measurements supported the well-known streamer breakdown theory