Breakdown at window interfaces caused by high power microwave fields

Breakdown phenomena at window interfaces are investigated for microwave power levels of up to 100 MW. The test stand utilizes a 3 MW magnetron operating at 2.85 GHz, coupled to an S-band traveling wave resonant ring. Various configurations of dielectric windows (i.e. vacuum-air, or vacuum-vacuum), in various geometries (standard pillbox geometry, or windows filling the S-band waveguide cross section) can be investigated. Diagnostics include the measurement of transmitted and reflected microwave power, luminosity from the discharge plasma, x-ray emission from initially free electrons, and electric field probes. All these quantities are measured with high amplitude and high temporal (0.2... 1 ns) resolution. Goals are to determine the physical mechanisms -such as the dominant electron multiplication process - leading to flashover. The knowledge gained from these experiments will be used to investigate and design methods to increase the power density which can be transmitted through windows. In addition, parametric studies are planned, in which window material, profile, and surface coatings are varied. The basic system and the diagnostics methods will be expanded for the investigation of microwave cavity breakdown as well.