磁旋返波振盪器係利用電子迴旋脈射機制產生同調電磁波，利用電子與波的內部反饋迴路產生振盪，而非採用傳統共振腔結構，因而有連續可調的寬頻調頻之特性，在研究與實用上都有很大的發展潛力。然而，因為其場型會往作用結構的前端集中，不利於電子與波的交互作用，所以其效率通常相當低，因此探討磁旋返波振盪器的基本特性與效率之提升是本篇論文的主要脈絡。
做為與以往Ka頻段的磁旋返波振盪器模擬結果之比較及驗證，本文根據已設計好的W頻段MIG電子槍之工作參數為依據，以W頻段的磁旋返波振盪器為研究對象，做理論上的計算探討。
在小訊號的線性操作之下，根據電子與電磁波的交互作用形式，能量吸放的次數之不同，造成不同的軸向模式；而在飽和電流的非線性操作下，因為內部反饋迴路的縮短，造成場型逐漸往上游端收縮，因而形成效率對電流或長度的飽和現象。
接著，我們根據以往經驗提出的方法，適當地傾斜磁旋返波振盪器之作用結構的半徑，以提升效率。模擬結果顯示，我們的雙傾斜結構設計在振盪頻率94GHz至99GHz可給出約23%至30%的效率，達到穩定而寬頻的高功率輸出。

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.

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