Abstract
The gyro-BWO(gyrotron backward wave oscillator) is a promising source of coherent millimeter-wave based on the ECM(Electron Cyclotron Maser) interaction. The facts that oscillation is formed by an internal feedback loop enables a gyro-BWO to use a non-resonant structure, hence the frequency of a gyro-BWO can be tuned broadly and continuously. However, the facts that the field profile tends to concentrate in front of the interaction structure when a gyro-BWO is working, strongly affects the interaction between electrons and wave, and this usually ruins the efficiency of a gyro-BWO. Hence the main idea of this study is to realize the basic characteristic and enhance the efficiency of a gyro-BWO. W-band gyro-BWO is the main target of this study, and all the working parameters of this study is based on our W-band MIG gun, which has been designed and fabricated by Dr. C.P. Yuan, and the result is compared with our previous study on Ka-band gyro-BWO. In small-signal operation, the behavior of the gyro-BWO is linear. The number of axial modes is strongly related to the times of energy deposition between electrons and wave. On the other hand, in nonlinear operation, the efficiency saturates with growing current or interaction length, which is result from the contraction of the internal feedback loop and hence contracts the field profiles. Last of all, according to previous paper, we do some optimize to enhance the efficiency of W-band gyro-BWO by tapering our interaction structure quiet smoothly. The result shows that our by-tapering structure gives about 23%~30% in efficiency from 94GHz to 99GHz in oscillation frequency.