Microwave Breakdown of Water Vapor

Continuous wave breakdown electric field strengths of water vapor have been measured by a resonant cavity technique at 2.45 GHz, in the pressure range from 20 mtorr to 22 torr. Two cavities were used, one having a characteristic diffusion length of 0.39 cm and the other of 1.0 cm. The results, including a minimum breakdown threshold of 165 V/cm, occurring at a pressure of 1.4 torr, are typical of a combined diffusion and attachment-controlled gas breakdown. These data are required for an investigation of a microwave-aided freeze-drying process.