光陰極超導射頻電子槍中之空間電荷動力學探討

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研究生：	陳鐶洋 Huan Yang Chen
論文名稱：	光陰極超導射頻電子槍中之空間電荷動力學探討 Investigation of Space Charge Beam Dynamics in a Photocathode Superconducting RF Gun
指導教授：	蕭憲彥 Sen Yen Shaw
口試委員:
學位類別：	碩士 Master
系所名稱：	電機資訊學院 - 電機工程學系 Department of Electrical Engineering
論文出版年：	2005
畢業學年度：	93
語文別：	英文
論文頁數：	51
中文關鍵詞：	空間電荷、射頻電子槍、光陰極
外文關鍵詞：	Space charge, RF gun, photocathode
相關次數：	點閱：2 下載：0
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近年來，不管是在工程發展、物理研究與商業應用上，對於可以提供高品質電子束的電子槍的需求日益增加。相較於傳統的熱陰極電子槍，新一代所發展的光陰極射頻電子槍可提供短脈衝、高密度、低空間發散度的電子束，可應用在電子顯微鏡、離子佈植與高功率微波儀器......等工業應用上，也是對撞機、同步輻射光，自由電子雷射的重要電子束源，在高能物理以及核子物理的研究上扮演重要的角色。本篇論文主要是以國家同步輻射中心在2003年所提出的窄線寬高平均功率遠紅外光自由電子雷射計劃當中的電子注射系統為研究主題，目的是希望設計出一個電子注射系統可以提供高平均電流、低空間發散度的電子束。我們以電腦模擬程式---PARMELA與SUPERFISH，來探討在一個光陰極超導射頻電子槍中的電子動力學，除了考慮超導射頻電子槍中的加速電場影響外，電子束團中的空間電荷效應也一並考慮。首先以電腦模擬的結果與理論分析作數據比較，發現在某些情況下結果相當吻合，以此結果作為電子注射系統設計的理論基礎。接下來研究在Forschungszentrum Rossendorf 3.5共振腔的光陰極超導射頻電子槍中，電子的運動情形以及各項變因的交互影響。在先前研究結果的基礎下，我們設計一個1.5共振腔的光陰極超導射頻電子，並以射頻場聚焦改善電子束團的空間發散度。藉此我們可以得到一個電荷數1nC、能量3MeV、能散度0.9%以及空間發散度8mm-mrad的電子束團，以符合國家同步輻射中心自由電子雷射計劃對於進入線型加速器前電子束團品質的要求。

Dynamics of space charge beam has been investigated in a photo-cathode superconducting radio frequency electron gun by a marco-particle tracking code, PARMELA. Results have been verified by analytical theory of laser driven rf gun, it agrees well at certain injection phases. The exemplary case of Forschungszentrum Rossendorf 3.5cell superconducting radio frequency photoinjector has been analyzed. A 1.5 cell high duty superconducting radio frequency photoinjector has been designed to meet the requirement of the proposed NSRRC narrow-bandwidth and high power IR FEL; satisfactory beam quality has been obtained. A 1nC, 3 MeV beam with rms normalized emittance at 8 mm-mrad can be achieved by optimizing the RF focusing field near the cathode.

1  Introduction    1
    1.1 Overview of injectors    1
    1.2 Photoinjectors    2
        1.2.1 DC photoinjector    2
        1.2.2 Normal-conducting RF photoinjector    3
        1.2.3 Superconducting RF photoinjector    5
    1.3 FEL beam requirement    5
    1.4 IR-FEL proposal    7
    1.5 Key points of this research    8
    1.6 Introduction of each chapter    8
2  Theory for RF and Space-Charge Effects in
    Laser-driven RF Electron Gun    9
    2.1 Introduction    9
    2.2 RF acceleration    11
    2.3 RF effects on longitudinal phase space distribution    13
    2.4 RF effects in transverse phase space    14
    2.5 Space charge effects on beam emittance    15
3  Chapter 3 Method    16
    3.1 Simulation tool    16
        3.1.1 PARMELA    16
        3.1.2 Superfish    17
    3.2 Strategy of data run    18
4  Simulation results    20
    4.1 Verification of Kim’s model    20
    4.2 Exemplary case of FZR 3.5 cell SRF photoinjector    24
        4.2.1 Geometry of srf gun and field distribution    25
        4.2.2 Variation of the beam distribution on phase space    27
        4.2.3 Analysis of beam cutoff radius    31
    4.3 Analysis and Design of 1.5 cell SRF photoinjector    33
        4.3.1 Geometry of 1.5 cell SRF photoinjector    33
        4.3.2 Input beam setting    34
        4.3.3 Simulation results    36
        4.3.4 Emittance compensation---RF focusing    38
5  Conclusion: Summary and future direction    41
Appendix    43
    A  PARMELA test    43
        A.1 Particle distribution of beam    43
        A.2 Verification of the SCHEFF calculation    44
        A.3 Convergence test --- time & spatial    46
    B  Superfish test    47
        B.1 Convergence test --- field & frequency    47
Reference    49

                                

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John Wiley & Sons, Inc., 1994

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