Microwave window breakdown

Dielectric windows separating vacuum from atmospheric pressure are essential in the operation of high power microwave devices and linear accelerators. Due to the large electric fields associated with high power microwave and linear accelerator devices, breakdown and flashover across the dielectric window is a commonly occurring phenomenon. Since the physical mechanisms leading to dielectric window failure are not fully understood, the advancement of high power devices utilizing dielectric windows is currently limited.

A microwave system capable of monitoring and acquiring data geared toward the pre-window breakdown mechanisms has been created through the union of a traveling wave resonator and coaxial magnetron. The system consists of a high voltage DC power supply to charge a pulse forming capacitor network. The capacitor network is discharged to a pulse transformer, which is directly attached to the cathode of the magnetron. The microwaves are axially extracted from the magnetron to the traveling wave resonator, or ring resonator, and are applied to a dielectric window contained in the ring. As the traveling wave circumnavigates the ring, the power level will increase eventually causing a dielectric window breakdown. High speed diagnostics present on this system include forward and reverse power couplers and field probes to monitor the microwave power and field at the dielectric window. Luminosity and soft x-ray emission were recorded through high speed optical sensors. High purity alumina is the focus for this experiment, but rexolite is investigated and compared to the alumina results.