OPERATION OF A RELATIVISTIC BACKWARD-WAVE OSCILLATOR FILLED WITH A PREIONIZED HIGH-DENSITY RADIALLY INHOMOGENEOUS-PLASMA

A modified relativistic (500 kV, 500 A) backward-wave oscillator (BWO) filled with a radially nonuniform preionized plasma of high-peak dens ity (peak plasma frequency > operating frequency) is studied experimen tally. The effects of high plasma density in the interaction region as well as the relativistic diode and the output horn regions were studi ed. By protecting both the diode and output regions against plasma pen etration, the plasma effects on the BWO was studied up to a peak plasm a density of 8 . 10(12) cm(-3). It was demonstrated that filling the B WO structure with high density radially nonuniform plasma leads to the following. 1) Suppression of high-order modes. This is a promising ap proach for implementing single mode operation of high-power large-diam eter overmoded devices, 2) Frequency upshift of up to 30% (from 8.5 to 11 GHz), This demonstrates the possibility of electronic frequency tu nability by controlling the plasma density. 3) Substantial increase in the measured microwave output power for n(p) > 10(12) cm(-3) over the corresponding vacuum value.