磁旋返波震盪器是利用電子迴旋脈射機制(electron cyclotron maser)產生同調電磁波，並且利用電子與波的內部反饋迴路產生振盪，與傳統共振腔結構有所不同，因而具有連續可調的寬頻調頻特性，所以在研究以及實用上都有很大的發展潛力，但是由於非線性場型收縮的特性，能量轉換效率相對較低；操作在四次諧波可以讓軸向靜磁場只需原來的四分之一，大大降低實驗成本困難度，但高次諧波的效率不高，也造成起振電流較高，且又有其他諧波競爭，因此頻寬相對狹小；綜合以上，探討磁旋返波振盪器的效率的提升並且讓頻寬更加寬廣便是本篇論文的主題，並了解其結果背後的物理特性。
本文是以在400GHz頻段下，以後可以應用於MRI、ESR和蛋白質分析等等；選擇 ，並且使用幾乎設計好的CUSP電子槍，由其guiding-center position近乎於零的特性讓 的模式不會被起振，大大降低模式競爭；在線性程式模擬操作下，電子與電磁波不同的優化傳輸角造成不同的優化起振電流，也對應到特徵頻率和電子能量吸吐次數之不同的軸向模式；而在非線性程式模擬操作區間，因為電流的提高，造成場型逐漸往電子入口處集中，而形成效率或起振電流對長度的飽和現象。為了提升振盪器的效率以及頻寬，我們針對波導管的幾何結構進行改變，並且也加入靜磁場的變化，以程式模擬優化效率及頻寬為最終目的。

Harmonic operation could alleviate the requirement of strong magnetic field which is the major difficulty for terahertz gyrotrons. This work presents a theoretical investigation of a 4th harmonic 400 GHz gyrotron backward-wave oscillator (gyro-BWO) with relatively high efficiency and broadening bandwidth. An axis-encircling electron beam is employed to suppress the mode competition. The operating mode is the TE41 mode. The efficiency and bandwidth are optimized for the magnetic field tuning. Simulations suggest that the 4th harmonic circuit is capable of achieving highest interaction efficiency and most broadening bandwidth.

內文目錄
摘要 I
內文目錄 II
附圖目錄 IV
第一章 緒論 1
1.1 Terahertz微波簡介 1
1.2 磁旋管簡介 3
1.3 電子槍簡介 8
1.4 電子迴旋脈射原理 10
1.5 諧波交互作用(Harmonic interation) 13
第二章 非線性理論計算公式 16
2.1 電磁波的場方程式 17
2.2 電子動力學 21
2.3 電子初始分佈 24
2.4 邊界條件 26
2.5 轉換至慢速座標 28
第三章 磁旋返波振盪器介紹與特性 32
3.1 磁旋返波振盪器的基本原理及特性 32
3.2 磁旋返波振盪器的線性行為 33
3.3 磁旋返波振盪器的飽和行為 39
第四章 400GHz TE41 第四諧波磁旋返波振盪器頻寬和效率之優化 42
4.1 波導管長度的決定 45
4.2 向下緩變傾斜結構(down-tapered waveguide) 49
4.3 向上緩變的軸向靜磁場 58
第五章 結論 65
參考文獻 67

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