Characterization of the UNM long-pulse BWO experiment

Long-pulse high power microwave experiments are being conducted at the University of New Mexico (UNM) using a modified Physics International Pulserad 110A. The Pulserad 110A, which previously consisted of an 11-stage Marx bank followed by a Blumlein, has been modified by replacing the Blumlein with a parallel L-C network, as described by Cummings. Both the Marx bank and the L-C network together form a type-A pulse-forming network with an output impedance of 40 /spl Omega/, a pulse duration of 500-700 ns, and a peak voltage and current for a matched load of 570 kV and 14.3 kA, respectively. The UNM Pulserad 110A drives an electron beam diode having a graphite annular knife-edge cathode. The electron beam that is generated is injected into a slow wave structure (SWS) having 12 periods with variable ripple amplitudes. Microwave radiation in the TM/sub 01/ mode is observed with peak powers on the order of 170 MW and pulse widths at full-width, half-maximum of 20-25 ns. Longer pulse widths are observed for lower powers. Studies are being conducted to determine the effects of changes in the anode-cathode gap spacing and cathode diameter on pulse duration for a given SWS configuration. Both vacuum and plasma-filled experiments are being performed to investigate possible increase in pulse width using plasma filling. The system design will be presented along with experimental results.