發展在電漿波導式雷射電漿波電子加速器中誘發電子注入與X 光產生之技術; Induction of electron injection and X-ray generation in a plasma -waveguide -based laser wakefield electron accelerator

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题名:	發展在電漿波導式雷射電漿波電子加速器中誘發電子注入與X 光產生之技術;Induction of electron injection and X-ray generation in a plasma -waveguide -based laser wakefield electron accelerator
作者:	何彥政;Ho,Yen-cheng
贡献者:	物理學系
关键词:	雷射電漿波電子加速器;電漿波;電漿波導;Laser wake field accelerator;Plasma wave;Betatron oscillation;Bubble regime;Plasma waveguide
日期:	2013-07-22
上传时间:	2013-08-22 11:47:12 (UTC+8)
出版者:	國立中央大學
摘要:	雷射激發的尾跡場 (wakefield) 可支撐強度達1GV/cm 的電場，非常有機會成為下一代的主流加速器。線性啾頻脈衝放大技術 (chirp pulse amplification) 的引入讓雷射脈衝的尖峰功率達到兆瓦 (TW) 或甚至拍瓦 (PW)，而聚焦後高強度雷射脈衝的縱向光壓可以激發一個大振幅的電漿尾跡場來加速電子。此技術已經達成在公分尺度的距離將電子加速到GeV 的能量，並開始研發如何以此電子束激發產生頻譜落在兆赫茲到X 光的高亮度的光子源。此領域最重要的議題就是電漿尾跡場中的電子注入和加速過程，他們會影響產生電子的品質和發與發之間電子參數的穩定度以及此加速器可達到的最高電子能量。此論文報告了本人發展在電漿波導中實現雷射尾跡場電子加速以及利用電子迴旋器振盪 (betatron oscillation) 輻射出X 光的研發成果。第一部分的工作，主要是用系統性的實驗方法研究利用氣態靶摻入特殊氣體的游離引發電子在雷射尾跡場加速器的注入。以摻入少量氬氣的氫氣當作氣態靶，可將產生單能電子束所需的主雷射脈衝能量閥值降低許多，並有效抑制低能量電子背景的產生。我們也成功的在以圓錐透鏡結合點火加熱機制 (axicon-ignitor-heater scheme) 產生的電漿波導中以雷射激發的電漿尾跡場加速電子，若一樣以摻入少量氬氣的氫氣作氣態靶，同樣可降低在電漿波導中注入電子的主雷射脈衝能量閥值。在第二部分的工作，我們先發展產生可調式三維結構電漿波導的技術，主要是利用從側向疊加一道橫向加熱脈衝到圓錐透鏡結合點火加熱機制產生的電漿來達成。利用此技術，我們可以在此電漿波導中以雷射激發的電漿尾跡場加速產生能散極小的單能電子束，此注入電子的機制和一段橫截面膨脹電漿波導有關。除此之外，我們也可以在電漿波導中製造一段橫向位移的橫截面結構，成功的增加電子迴旋器振盪振福，大幅提高輻射出的X 光強度。此技術開啟了實現超小型X 光脈衝光源的新方向。 Laser driven wakefield is capable of sustaining field in excess of 1 GV/cm, making it a promising candidate for the next-generation electron accelerator. The development of chirp pulse amplification boosts the power of laser pulse to terawatt (TW) or even petawatt (PW) level, making it possible to drive a large-amplitude plasma wave to accelerate electrons by the poderomotive force of the intense focused laser pulse. This technique has achieved GeV electron energy in centimeter scale and is being investigated as a driver for generating bright photons with spectrum ranging from THz to X-rays. The most important issues in this field are injection and acceleration process in the driven plasma wave, which determines the quality and shot-to-shot stability of the electron beam and the highest energy gain one can obtain from the accelerator. This thesis reports the efforts and accomplishments on the development of a plasma-waveguide-based Laser wakefield accelerator with two kinds of new electron injection scheme and channel betatron radiated X-ray source. In the first part of my work, a systematic experimental study on injection of electrons in a gas-jet-based laser wakefield accelerator via ionization of dopant was conducted. The pump-pulse threshold energy for producing a quasimonoenergetic electron beam was significantly reduced by doping the hydrogen gas jet with argon atoms, resulting in a much better spatial contrast of the electron beam. Furthermore, laser wakefield electron acceleration in an optically preformed plasma waveguide based on the axicon-ignitor-heater scheme was achieved. It was found that doping with argon atoms can also lower the pump-pulse threshold energy in the case with a plasma waveguide. In the second part of my work, a variable three-dimensionally structured plasma waveguide was fabricated by adding a transverse heater pulse into the axicon-ignitor-heater-scheme. With this technique, induction of electron injection in a plasma-waveguide-based laser wakefield accelerator was achieved and resulted in production of a monoenergetic electron beam. The injection is correlated with a section of expanding cross-section in the plasma waveguide. Moreover, the intensity of the X-ray beam produced by the electron bunch in betatron oscillation was greatly enhanced with a transversely shifted section in the plasma waveguide. The technique opens the route to a compact hard x-ray pulse source.
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