Experimental Study of a High-Power Backward-Wave Oscillator Operating Far from the Upper Cutoff

Abstract

The characteristics of a high-power backward-wave oscillator (BWO) operating far from the upper cutoff, i.e., “π” mode of a corrugated waveguide, are investigated experimentally. The high spectral purity of output power of the TM 01 mode is maintained for large beam currents, because the starting currents of device have large values in this regime. It is observed that, when the beam currents are less than the starting current of the TM 01 mode, hybrid TE 11 mode is excited in the BWO. Peak output powers of 5.3 MW at 7.2 GHz in TE 11 mode and 6.8 MW at 8.5 GHz in TM 01 mode are generated. The conversion efficiencies are about 13% and 11%, respectively. These experimental results indicate a possibility of improved performance in high-power and high efficiency relativistic BWO by controlling the operation regime.