General scaling of pulse shortening in explosive-emission-driven microwave sources

Microwave generation in devices that depend on synchronization between an electron beam and a resonant cavity or slow wave structure can be disrupted by changes in either. Explosive-emission-driven microwave sources use plasma as the electron source in the diode. This plasma is conductive enough to act as the boundary for both the applied diode voltage and the microwave electric field. The motion of this plasma can effectively change the dimensions of either the electron beam diode or the cavity and will thereby cause resonance destruction. This shortens the microwave pulse length /spl tau//sub /spl mu//. A general model of the process predicts that, for a Child-Langmuir diode, microwave power falls as P/spl prop//spl tau//sub /spl mu///sup -5/3/ and that pulse energy falls as E/spl prop//spl tau//sub /spl mu///sup -2/3/. Therefore, energy efficiency declines as the pulse length is extended. We compare with data from magnetrons, MILO's and BWO's, and find that over some regions of operation the pulse length and energy from these explosive-emission-driven microwave sources agree with the plasma motion model scaling. At these applied drive voltages and output powers the microwave pulse length can be increased by finding cathode materials that generate slower plasmas.