EXPERIMENTAL-STUDY OF A HIGH-POWER BACKWARD-WAVE OSCILLATOR OPERATINGFAR FROM THE UPPER CUTOFF

The characteristics of a high-power backward-wave oscillator (BWO) ope rating far from the upper cutoff, i.e., ''pi'' mode of a corrugated wa veguide, are investigated experimentally. The high spectral purity of output power of the TM01 mode is maintained for large beam currents, b ecause the starting currents of device have large values in this regim e. It is observed that, when the beam currents are less than the start ing current of the TM01 mode, hybrid TE11 mode is excited in the BWO. Peak output powers of 5.3 MW at 7.2 GHz in TE11 mode and 6.8 MW at 8.5 GHz in TM01 mode are generated. The conversion efficiencies are about 13% and 11%, respectively. These experimental results indicate a poss ibility of improved performance in high-power and high efficiency rela tivistic BWO by controlling the operation regime.