TE01模磁旋返波震盪器之研究

TE01 Gyrotron Backward-Wave Oscillator

余青芳(Ching-Fang Yu)

指導教授 ： 張存續

國立清華大學/理學院/物理學系/博士(2006年)

摘要

磁旋振盪器是利用電子迴旋脈射原理而產生與電子同調的電磁波，磁旋返波振盪器有頻率連續可調與寬頻寬的特性，操作的電磁波模式廣範地選用最低基本模式以簡化實驗及避免高次模競爭，但在高頻段的發展趨勢下，高次模操作可有效解決高頻率結構過小的問題。本論文設計並實做一ka頻段緩斜結構的圓形波導TE01模磁旋返波震盪器， TE31模式一次諧波振盪是影響操作穩定的主要競爭模式。利用穩定解計算程式模擬主模與各競爭模的起振電流以判斷穩定操作條件，因單模耦合器輸出對非主模式所造成的之短路邊界亦在模擬中考慮，在利用加入分佈式吸波作用段可有效壓抑非主模振盪。
實驗系統中包含一新式高效能圓形波導TE01模耦合器，其高純度轉換率能避免因耦合輸出造成的模式轉變，在對接特性測量中得出穿透率達97%而1-dB頻寬於34GHz中心頻率達5.8GHz並與模擬高度吻合。
初階段實驗結果指出分佈式吸波作用段確實可有效壓抑非主模振盪而達穩定操作，最高輸出能量為46kW，效率與頻寬各為8%及3.7%。

關鍵字

磁旋返波 ； 震盪器

並列摘要

The gyrotron backward-wave oscillator (gyro-BWO) is a continuously tunable source of coherent millimeter-wave radiation based on electron cyclotron maser. The fundamental mode operation is generally adopted to simplify the experiment which can avoid the mode transition problem and the mode competition behavior. As the high frequency requirement increase, high order mode operation is an effective method to solve the structure size limit. A taper structure Ka-band gyro-BWO which operated at TE01 mode in cylindrical waveguide is designed in this thesis. The mode competition behavior is discussed which major unwanted competing mode is TE31 first harmonic oscillation. A single mode stationary code is employed to simulate the start oscillation current and nonlinear behavior of each interaction mode. The relative value of start oscillation current between operating mode and the other waveguide modes are applied to judge the operating stability. The question which we must consider is the short end boundaries to the TE31 mode. As a result, the close cavity structure brings about the gyromonotron dynamic which have lower oscillation threshold. A distributed loss is applied to suppress the unwanted oscillation but operating mode.
A novel design and of high spectral purity Ka-band TE01 mode converter are presented to avoid the mode transition when wave coupled out. Back-to-back transmission measurements show excellent agreement with computer simulations. The measured optimum transmissions are 97% with 1-dB bandwidth of 5.8 GHz at center frequency 34 GHz. In addition to high conversion efficiency, high mode purity, and broad bandwidth, this converter also features easy construction and compact size.
The preliminary experimental results show the spurious modes can be suppressed by distributed loss. The maximum output power is 46kW with efficiency 8% and the bandwidth is 3.7%.

並列關鍵字

TE01 ； Gyrotron ； BWO

參考文獻

1. K.R. Chu, Rev. Mod. Phys. 76(2), 489, 2004.

2. P. Forman, Rev. Mod. Phys. 67, 397, 1995.

4. V. L. Granatstein, B. Levush, B. G. Danly, and R. K. Parker, IEEE Trans. Plasma Sci. 25, 1322, 1997.

7. S.H. Gold and G. S. Nusinovich, Rev. Sci. Instrum. 68, 3945, 1997.

9. A. W. Fliflet, Int. J. Electron. 61, 1049 1986.