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研究生： 范肇達
Chao-Ta Fan
論文名稱： 磁旋返波振盪之穩定性與調變性研究
Stability and Tunability of a Gyrotron Backward-Wave Oscillator
指導教授： 張存續
Tsun Hsu Chang
朱國瑞
Kwo Ray Chu
口試委員:
學位類別： 博士
Doctor
系所名稱： 理學院 - 物理學系
Department of Physics
論文出版年： 2005
畢業學年度： 93
語文別： 中文
論文頁數： 102
中文關鍵詞： 磁旋管 、穩定性 、調變性 、非線性行為 、磁旋返波振盪器
外文關鍵詞： gyrotron, stability, tunability, nonlinear, gyro-BWO
相關次數： 點閱：2  下載：0 
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    • 磁旋返波振盪器是利用電子迴旋脈射機制（Electron cyclotron maser）而產生電磁波，因此具有高功率與寬頻的特性，在整個毫米及次毫米波源佔有相當重要的地位，然而它的發展卻受限於不穩定性的振盪。在這篇論文中，我們將就其基本物理特性，研究其線性與非線性的行為，探討其不穩定振盪的原因，並藉由其基本物理特性研究其調變性。

    在線性操作區間，電子與電磁波能量間互相的吸吐形成了軸向模式；而在非線性操作時，軸向場會逐漸向上游集中，而形成場形收縮（field contraction），並利用時變計算程式瞭解其在作用長度較短時，可高效率穩定地操作於高電流，表現出磁旋返波振盪器的特性-寬頻寬的調變特性，並藉由此瞭解在作用長度較長時不穩定振盪的原因-自我調制（self-modulation）。而我們也成功地進行Ka頻帶的磁旋返波實驗，證明其在作用長度較短時（Lo=3.0 cm），輸出訊號可以穩定地的操作，最高效率也可達28％，然而當作用段長度為9公分時，其調變卻受到不穩定振盪的限制，無法有寬頻的操作，效率也僅僅約20％。而不穩定振盪的成因方面，我們在實驗上利用訊號時閘的技術，觀測到磁旋返波振盪器在作用長度較長時，由於電子與電磁波的能量供需不均而自我調制的情形，因此輸出的頻譜上形成在主要頻譜上有兩邊等距的旁帶訊號（sidebands），最後造成不穩定振盪。

    The gyrotron backward-wave oscillator (gyro-BWO) base on electron cyclotron maser is a promising millimeter/submillimeter source for high power capability and broad band tunability. However, the development of the gyro-BWO is hampered by the nonstationary oscillation. We will discuss the stability and tunability form the fundamental physics characters and verify by the Ka band gyro-BWO experiment.

    The beam-wave interaction forms the axial mode in the gyro-BWO. The number of regions of positive energy deposition rate determines the order of axial mode in the linear operating region. The field contracts to the beam entrance at the nonlinear operating region. The time-dependent particle-in-cell code is used to analyse the nonlinear behavior in the gyro-BWO. The results show the gyro-BWO exhibits the broad and stationary tunability at the shorter interaction length. And the self-modulation could be the reason forming the nonstationary oscillation in the gyro-BWO. We conducted the Ka band gyro-BWO experiment to verify the tunability at the shorter interaction length (3 cm) and analyse the stability at the longer interaction length (9 cm). The experimental results show that the gyro-BWO could broad and stationary operation at the 3 cm interaction length with maximum efficiency 28%, whereas the nonstationary oscillation hampered the tunability at the 9 cm length with 20% efficiency. The signal gating technique was used to analyse the spectra of the nonstationary oscillation. The uneven spatial distribution of the beam deposited energy causes the field energy to bounce back and forth within the feedback loop and modulates the oscillation amplitude and generates the equally spaced sidebands about a main peak in the output spectra.

    目錄 1. 序論 1 1.1慢波結構與快波結構 3 1.2毫米與次毫米波段的窗口 7 1.3磁旋管 9 1.4磁旋返波振盪器的潛力及研發概況 14 1.5論文概觀 16 2. 非線性理論計算公式 18 2.1電磁波場方程式 18 2.2電子動力學 23 2.3初始電子分佈 26 2.4邊界條件 28 2.5轉換至慢速座標 30 3. 磁旋返波振盪器特性分析 34 3.1磁旋返波振盪器線性行為特性分析 37 3.2磁旋返波振盪器的飽和行為研究 42 3.3磁旋返波振盪器之非線性特性 46 3.4實際操作條件之穩定性分析 50 4. 實驗裝置與量測系統 56 4.1電子槍 57 4.2輸入與輸出耦合器 60 4.3輸出訊號的診斷 66 5. 實驗結果與討論 69 6.1緩變磁場之效果與分析 72 6.2作用長度對返波振盪器之調變影響與分析 77 6.3磁旋返波震盪器非線性行為(一) 84 6.4磁旋返波震盪器非線性行為(二) 91 6. 總論 98 參考文獻 100

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