Global model for high power microwave pulse breakdown in air and SF6

The breakdown in air and SF6 caused by a high power microwave pulse is investigated using a global model, respectively, in which the rate coefficients such as an ionization rate derived from the Boltzmann equation solver BOLSIG+ are adopted. The breakdown prediction from the global model agrees very well with experimental data. The relation curves among the effective breakdown threshold, pressure, and total duration of pulse with either different frequencies or different duration of pulse are nearly the same, but change with the background gas species. At atmospheric pressure, the breakdown threshold of SF6 for a long microwave pulse is about three times larger than that of air. However, the ratio decreases, when the gas pressure or the total duration of pulse is decreased.