Study on Oscillation Starting Condition of K-Band Oversized Backward Wave Oscillator Driven by a Weakly Relativistic Electron Beam

Abstract

Oscillation starting condition of a K-band oversized backward wave oscillator (BWO) is investigated experimen-tally. Periodically corrugated slow-wave structure (SWS) is used, which is designed for K-band operation in a weakly relativistic region, i.e. 30-80 kV. The beam current is in the range of 50-200 A. It is shown experimentally that there exists a critical beam energy (starting energy) for the meaningful radiation. The starting energy is more critical than the starting current in the oversized BWO. It decreases by increasing the SWS length. Above the starting energy, the out-put powers up to about 100 kW are obtained. The typical frequency observed is about 23 GHz. Nonaxisymmetric hybrid HE11 mode as well as axisymmetric TM01 mode is observed. The operation mode is able to be controlled by the SWS length and the magnetic field strength. Keywords: oversized backward wave oscillator, K-band, weakly relativistic electron beam, axisymmetric mode, nonaxisymmetric mode, starting energy Slow-wave high-power microwave devices such as backward wave oscillator (BWO) and traveling wave tube can be driven by an axially injected electron beam without