Progress In The Long-pulse BWO Experiment At The University Of New Mexico

Abstract

High power microwave experiments using a long pulse accelerator with a backward wave oscillator (BWO) are continuing at the Pulsed Power and Plasma Science Laboratory of the University of New Mexico. The accelerator used in this study is a Physics International Pulserad 110A, which has a 2.75 kJ Marx bank as its primary energy store. In order to convert this accelerator to long pulse operation, the original pulse forming line was placed with a parallel L-C network, thus giving rise to a new cathode voltage, impedance, and pulse duration for the Pulserad 110A of 500 kV, 40 {Omega}, and 450--550 ns, respectively. The accelerator drives an electron gun, which has an annular, knife-edge, carbon cathode that is approximately 2 cm in diameter. The relativistic beam that is emitted from the gun is injected into a slow wave structure (SWS) to generate X-band microwaves. Currently, the SWS is configured such that there is a non-uniform variation in the amplitude of the ripples in the wall, similar to companion short-pulse experiments that are being conducted here. Microwave power levels in recent experiments have been as high as 140 MW with pulse durations ranging from 16 to 32 ns. Damage observed inside themore » SWS after experiments indicates that a significant amount of breakdown is occurring. High rf fields may be a major cause of the early cessation of microwave radiation. The system design will be presented along with data from further vacuum SWS experiments. Detailed plans for plasma-filled SWS experiments and preliminary data from these experiments will also be presented.« less