為了追尋高亮度的加速器輻射光子源，如何穩定有效的產生相對論性之超短電子脈衝是近年在電子加速器發展中的重要議題。飛秒級超短脈衝的電子束可以應用在多種先進前端的輻射光源上，例如自由電子雷射光源、逆康卜頓散射X光源、以及同調性的太赫茲光源。利用熱陰極電子腔可以產生穩定的電子源，但是熱陰極電子腔加速器的研究在過去並未深度開發。我的論文研究，便利用熱陰極電子腔加速器系統為主題，挖掘探討產生穩定超短電子脈衝的潛力及可能性。
典型的熱陰極電子腔加速器系統中，在熱陰極電子腔的下游包含了α-磁鐵以及直線加速器。我的研究指出，熱陰極電子腔所產生的電子束其空間電荷力是不可忽視的。在熱陰極電子腔系統的低能量階段，電子束的空間電荷力會伴隨著電子脈衝的壓縮過程而增長，因此造成電子脈衝在縱向相位空間上分布的變形。因此相對於過去熱陰極電子加速腔系統利用α-磁鐵的脈衝壓縮機制，我提出了利用電子束在下游傳遞波直線加速器中同時加速及壓縮的方式，以緩和伴隨電子脈衝壓縮所增益之空間電荷力。此種方式稱為所謂的在傳遞波線型加速器內的速度群聚壓縮效應，飛秒級的超快電子脈衝因為此項機制的引入將可以更有效率的穩定產生。論文裡將會探討如何在熱陰極電子腔加速器系統內產生此超短電子脈衝的策略，以及整體系統中電子束的空間電荷動力之深度分析。
為了在傳遞波直線加速器裡產生最佳化的速度群聚壓縮，我們提出了一個先進的熱陰極電子腔。此特殊的熱陰極電子腔具有兩個互相獨立的微波共振單元腔，因次兩個單元腔體的微波場強和腔體間的相對微波相位差可以被獨立調控。此項機制帶來調製電子在縱向相位空間中分布的可能性。論文中我更提出實驗結果，藉由實驗結果的分析與比較，揭示電子在縱向相位空間中分布的調控確實可以利用此先進的電子加速腔來完成。最佳化的速度群聚壓縮將可以在此特殊熱陰極電子腔加速器系統中實現。

Intense relativistic electron beam having very short bunch length of a hundred femtoseconds or less is the key for many advanced applications such as free electron laser, Compton scattered x-ray, and coherent terahertz radiation. A radio frequency (rf) gun that adopts the thermionic cathode as the electron source is with the capability to produce multi-bunched electron beam stably. Nevertheless, the study of thermionic rf gun linac system has not been well invstigated so far. In this study, we intend to explore the potential ability of a thermionic cathode rf gun linac system for the production of sub-hundred femtosecond electron bunches.
The electron beam dynamics in a thermionic rf gun linac system which consists of an α-magnet and a traveling wave accelerating structure are thoroughly examined and analyzed. It is found that the space charge effects overrule the beam dynamics seriously in the low energy side of such injector system. We thererfore consider a scheme called velocity bunching in the traveling wave accelerating structure for generation of sub-hundred femtosecond beam. We have demonstrated that thermionic rf gun possesses a promising advantage for velocity bunching. The compressed beam with bunch length of ~ 50 fs can be attained efficiently.
In order to optimize the beam longitudinal phase space for velocity bunching, a novel thermionic rf gun equipped two independent cavity cells has been developed. Since the coupling between the two cells is small, the electric field and the phase difference between two cells can be adjusted independently. This allows the flexible manipulation of electron distribution in the longitudinal phase space. The proof-of-principle experiment which shows this feasible manipulation has been demonstrated successfully in this study. The aggressive bunch compression in the thermionic rf gun linac system is made possible with this advanced electron rf gun.

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