Pressure dependence of high power microwave solid dielectric/gas interface breakdown

Summary form only given. The knowledge of the behavior of solid dielectric/gas interface breakdown caused by microwaves is crucial for developing new design methods for high power microwave windows. We investigate the physical mechanisms leading to breakdown for power levels on the order of 10 MW/cm/sup 2/ at 2.85 GHz and gas pressures varying from 10/sup -4/ to 10/sup 3/ Torr. As an interface that is in widespread use, the focus was put on an alumina/air interface. Other gases are considered mainly for reference purposes. The high power microwaves are generated with a 4 MW magnetron having a 3.5 μs pulse width in conjunction with an S-band traveling wave resonator. This approach provides a power gain of maximum 25, sufficient to cause breakdown across the interface located in the pressure adjustable test region. The interface geometry comprises a thin ceramic alumina slab placed in the waveguide center. We ensure an almost purely tangential field and a localized breakdown by orienting the alumina slab normal to the direction of the wave propagation and making contact with two field enhancement tips placed in the middle of each waveguide broad wall.