Window and cavity breakdown caused by high power microwaves

Summary form only given, as follows. Physical mechanisms leading to microwave breakdown on windows and in cavities are investigated for power levels on the order of 100 MW at 2.85 GHz. A 3 MW magnetron coupled to a traveling wave resonator is used. Various configurations of dielectric windows are investigated. In a standard pillbox geometry with a pressure of less than 10/sup -8/ Torr, surface discharges on an alumina window and multipactor-like discharges starting at the waveguide edges occur simultaneously. Window breakdown with purely tangential electrical microwave fields is investigated for special geometries. To access geometries relevant for vacuum-air interfaces, an air-filled two-window setup is integrated into the resonator as well. Diagnostics include the measurement of reflected/transmitted power, discharge luminosity, X-ray emission, and the measurement of local microwave electric fields. All quantities are recorded with 0.2 to 1 ns resolution. Based on the experimental results, methods to increase the power density which can be transmitted through windows will be investigated as well. In addition, parametric studies are conducted, in which window materials, profiles, and surface coatings are varied.