臺灣博碩士論文加值系統

雷射電漿加速器是利用雷射致發電漿波來加速電子。雷射電漿加速器可以提供遠超傳統射頻線性加速器的加速電場，在電子密度為1018 cm-3時，加速電場梯度最大可達100 GeV/m，是目前所有線性加速器的1000倍，此外也因為高加速電場梯度，使我們可以建造高能電子加速器在一般實驗室尺度般的小體積，而不用昂貴的建造經費，因此雷射電漿加速器具有成為下一代加速器的潛力。本論文將在第一章介紹雷射電漿電子加速器的發展簡史，第二章則介紹用短脈衝高強度雷射如何激發電漿波，及電漿波又如何捕捉電子加速的物理原理。
要產生能量集中的單能電子束，電子束必須要在特定的相位注入電子，其電漿密度和雷射脈衝也必須配合才能夠產生。第三章將討論實驗上如何產生單能電子束，我們產生的單能電子束的中心能量達49 MeV、極小發散角5 mrad、能量散佈22.4％，並且討論電子束與電漿密度、雷射能量、雷射脈衝寬度的影響。
論文第四章是設計利用橫向machining pulse搭配刀口(knife edge)移動的技術，在作用超音速噴嘴所產生的氣體上橫向產生線聚焦，來調變氣體的長度，稱為斷層掃瞄技術。利用這項技術，把以前只能用Particle-in-cell simulation預測電子束在電漿波的加速行為，直接在實驗上第一次觀測。我們發現電漿波產生後傳播950 mm時，單能電子束即注入，之後再傳播200 mm的加速距離電子能量便提升了50 MeV，加速梯度達250 GeV/m，低能的連續電子則比單能電子束早，在300 mm就已經注入，並且在300～800 mm這段距離一直有持續注入。單能加上連續電子的全部電子數達2.3 x1010， 單能電子束則佔了其中10％。第四章最後面則用物理模型說明電子束的注入機制。最後，我們在在第五章以本論文結果為基礎，提出未來電子加速器的設計方向。

In laser-plasma accelerators, the electrons are accelerated by the plasma wave generated by the laser pulses. For its large accelerating gradient, laser-plasma accelerators have greatly potential to be the next generation accelerators. For example, an accelerating gradient of 100 GeV/m can be sustained for 1018 cm-3 plasma density. Such an accelerating gradient is three order of magnitude larger than radio frequency linear accelerator. We can develop laser plasma accelerator in the small and compact size because of ultra high acceleration gradient. We briefly introduce history of laser-plasma accelerator in chapter 1.and we explain how to excite plasma wave by ultra-short laser pulse and discuss physic of trapping and accelerating electrons.
When laser pulse width match plasma density in a particular condition, the mono-energetic electron beam can be produced and accelerated in accelerating phase region of plasma wave. In chapter 3, we will discuss how to generate mono-energetic electron beam that peak energy 49 MeV, divergence 5 mrad, energy spread 22.4%.And also study the parameter dependence at plasma density, main pulse energy, main pulse width for mono-energetic electron beam.
We successful demonstrate in experiment of electron beam accelerating behaviors in the plasma wave moving frame by use of tomography technique. By making a transversely line focus (called machining pulse) into the laser-plasma interaction region produced by supersonic hydrogen gas jet valve and onset the knife edge tunable in horizontal position for covering the line focus beam. Thus, we can exactly measure the electron beam acceleration behaviors and there is only Particle-In-Cell simulation result in the past. The mono-energetic electron beam injected when plasma wave propagate about 950 mm, and accelerated 50 MeV in following 200 mm distance that acceleration gradient reach 250 GeV/m. Low and continuous (non mono-energetic ) electron beam is much earlier injected when plasma wave propagate about 300 mm, and acceleration lasted in 300~800 mm. All electrons reach 2.3 x1010 and mono-energetic fraction is 10%.Finally, we establish a physical model to explain the injection mechanism of electron beam. In chapter 5,we proposed future work of laser-plasma acceleration based on our results.

1 序論 1
1.1 發展雷射電漿波電子加速器的優勢.............................1
1.2 雷射電漿波電子加速器的發展歷史.............................2
1.3 十兆瓦雷射驅動光源.........................................5
2 雷射電漿波電子加速器的概述
2.1 電漿波的產生...............................................8
2.2 雷射電漿波加速器（laser wakefield accelerator，LWFA）.....10
2.3 電漿拍頻加速器（plasma beat wave accelerator，PBWA）......12
2.4 自調變雷射電漿加速器（self-modulated LWFA，SM-LWFA）......13
2.5 電子如何被電漿波捕捉加速..................................15
2.6 加速電子的能量限制........................................18

3 產生並量測單能電子束性質
3.1 實驗架設 氣體靶材.........................................19
3.2 實驗架設 空間上二維干涉儀（Mach-Zehnder interferogram）...22
3.3 實驗架設 電子束空間上x-y二維空間分佈量測系統（LANEX）.....26
3.4 實驗架設 電子能譜儀（EES)................................ 28
3.5 實驗結果 單能電子束指向性和單能電子束能譜處理及分析.......30
3.6 實驗結果 氣體密度與單能電子束關係.........................33
3.7 實驗結果 主脈衝雷射能量與單能電子束關係...................34
3.8 實驗結果 主脈衝雷射脈衝寬度以及啾頻與單能電子束關係.......35

4 用斷層掃瞄的方法（tomography）探究電子束加速機制 36
4.1 線聚焦搭配刀口控制電漿通道長短的物理機制及實驗架設........36
4.2 實驗架設 校正出作用氣體起始點和刀口成像位置...............39
4.3 實驗架設 使用高能電子能譜儀來量測電子束...................43
4.4 實驗結果 用單一主脈衝產生先產生單能電子束.................47
4.5 實驗結果 電漿波中電子束的注入點與加速梯度大小.............49
4.6 實驗結果 單能電子束能量成長飽和...........................54
4.7 物理說明 單能電子束被捕捉之加速物理機制...................55

5.結論與展望 57
參考文獻 59

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