破壞雷射電漿尾場加速之衝擊波前沿注入電子束之對稱性以產生線偏振 X 光源

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黃崧瑋(Sung-Wei Huang) 查詢紙本館藏

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破壞雷射電漿尾場加速之衝擊波前沿注入電子束之對稱性以產生線偏振 X 光源
(Generation of Linearly Polarized X-rays via Asymmetric Electron Beam Injection at the Shock Front in Laser Wakefield Acceleration)

相關論文

★ 優化雷射電漿加速器衝擊波注入電子品質之研究	★ 在雷射尾流場加速器中利用震波產生單能電子束
★ 雷射驅動相干性硬 X 光源的亮度增強

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摘要(中)

短脈衝的 X-ray 在科學和生物醫學中應用廣泛，而雷射電漿尾場加速（LWFA）產生的 Betatron 輻射是一種產生超短脈衝 X-ray 的方法。LWFA 利用短脈衝雷射與電漿交互作用加速電子，具有比傳統射頻加速器高約 1000 倍的加速梯度，因此無需大型實驗設施。在 LWFA 中，強橫向聚焦力使電子束在加速過程中震盪，類似波盪器的運動產生超短脈衝 X-ray。我們通過破壞衝擊波前沿的對稱性來增加電子束震盪強度，並用粒子模擬（PIC）驗證其可行性。利用 OSIRIS 模擬程式，我們成功再現了先前研究中的二維模擬 [1]，通過 15◦ 傾角破壞衝擊波前沿的對稱性，實現了單邊注入的電子束。進一步研究發現，只需降低雷射參數中的 ?0 並升高雷射束腰，即可在 15◦ 傾角傾角下達成完全單邊注 √入。然而，二維模擬與三維模擬的雷射演化條件不同，需要將二維模擬中的 ?0 除以 2 才能達到相似的雷射強度演化，但這會導致雷射束腰的演化差異，表明二維模擬無法討論更複雜的雷射演化現象。因此，我們使用三維 PIC 模擬探討傾角衝擊波前沿的條件。發現橫向注入電子束在 15◦ 傾角下無法完全單邊注入，且注入總電量與 0◦ 傾角相差不大。為達成單邊注入，我們將傾角增加到 65◦，成功產生單邊注入電子束。縱向注入電子束也是如此，只有在 65◦ 傾角下才達到 85 % 的單邊注入率，說明無論是橫向還是縱向注入電子束，三維模擬需更大角度才能實現高單邊注入率。為驗證單邊注入電子束的群體運動效應，我們追蹤電子束並分析其行為。結果顯示，橫向和縱向注入電子束在較大角度下平均震盪強度較強，且縱向注入角度越大，群體運動行為越強，但在另一方向的標準差差異也越大，意味輻射強度更強，導致降低了偏震度。光通量分析表明，縱向注入電子束的偏震度不隨角度增加而變化，與橫向注入的行為相反，後者隨傾角增加而偏震度增加，在 65 度傾角下達到 62% 的偏震度，因此橫向注入產生 X-ray 之偏震效果也越好。我們分析了橫向注入電子束的亮度，發現其在 65◦ 傾角下可產生阿秒等級、光通量高達 1020 之 X-ray。

摘要(英)

Short-pulse X-rays find universal applications in science and biomedicine. Betatron radiation generated from laser wakefield acceleration (LWFA) offers a method for pro- ducing ultrashort-pulse X-rays. LWFA utilizes the interaction between short-pulse lasers and plasmas to accelerate electrons, achieving acceleration gradients approximately 1000 times higher than conventional radio frequency accelerators, thus decreasing the need for large-scale experimental facilities. In LWFA, strong transverse focusing forces cause the electron beam to oscillate during acceleration, similar to the motion of an Wiggler, producing ultrashort-pulse X-rays. We enhanced the electron beam oscillation by breaking the symmetry of the shock front and verified its feasibility using particle-in-cell (PIC) simulations. By tilting the shock front by 15◦, we successfully reproduced the 2D simulation results in [1] and achieved single-sided electron injection. Further studies show that by reducing ?0 and increasing the laser waist at a 15◦, complete one-side injection can be achieved. However, the laser evolution conditions in 2D and 3D simulations differ. To achieve similar laser intensity evolution in 2D simulations, ?0 needs to be divided by √2, leading to differences in laser waist evolution. This indicates that 2D simulations cannot fully capture more complex laser evolution phenomena. Therefore, we employed 3D PIC simulations to investigate the conditions of the tilted shock front. It was found that transverse injected electrons could not be completely one- side injected at a 15◦, and the total injected charge was not significantly different from that at a 0◦. To achieve one-side injection, we increased the tilt angle to 65◦, successfully generating a one-side electron beam. Similarly, for longitudinal injected electrons, only at a 65◦ did we achieve an 85 % one-side injection rate, indicating that both transverse and longitudinal injected electrons require a larger angle in 3D simulations to achieve a high one-side injection rate. To verify the collective motion of single-sided injected electron beams, we tracked and analyzed their behavior. Results show that both transverse and longitudinal injections exhibit stronger average oscillations at larger angles, but longitudinal injections lead to larger deviations in the other direction, reducing polarization. Flux analysis indicates that transverse injections yield higher polarization, reaching 62 % at 65◦, while longitudinal injections show no angular dependence. We found that transverse injections at 65◦ can produce attosecond-level X-rays with a brilliance of 1020.

關鍵字(中)

★ 雷射電漿尾場加速
★ 衝擊波前沿注入
★ Betatron 輻射
★ 線偏振 X-ray

關鍵字(英)

★ LWFA
★ Shock Front injection
★ Betatron radiation
★ Linear polarize X-ray

論文目次

誌謝 xiii
目錄 xv
使用符號與定義 xxv

一、緒論 1
1.1 雷射電漿加速器之必要性..................................................... 1
1.2 利用電子加速產生之光源..................................................... 1

二、雷射電漿尾場加速之原理 3
2.1 電磁波與粒子的交互作用..................................................... 3
2.1.1 電磁波與單電子的交互作用........................................... 3
2.1.2 有質動力............................................................... 4
2.2 雷射與電漿的交互作用 ....................................................... 4
2.2.1 電漿中雷射的色散關係................................................ 5
2.2.2 電漿中雷射傳播的群速度 ............................................. 6
2.2.3 電漿中雷射的自聚焦與自調製 ........................................ 6
2.3 雷射電漿尾場加速中電漿波的產生........................................... 7
2.3.1 電漿波中的 (非) 線性範圍 ............................................ 7
2.3.2 電漿波中的氣泡結構 .................................................. 9
2.4 雷射電漿尾場加速的電子注入方法及其軌跡................................. 9
2.4.1 電離注入............................................................... 10
2.4.2 自注入 ................................................................. 10
2.4.3 衝擊波前沿注入 ....................................................... 10
2.4.4 光學注入............................................................... 11
2.5 雷射電漿尾場加速的 Betatron 輻射.......................................... 11
2.5.1 Heaviside-Feynman Formula .......................................... 11
2.5.2 方位角的光譜強度..................................................... 12
2.5.3 傳統加速器之波盪器輻射特性 ........................................ 13
2.5.4 雷射電漿尾場中的電子軌跡以及輻射特性............................ 13
2.5.5 偏振度計算 ............................................................ 14
三、二維雷射電漿尾場之模擬設置與結論 15
3.1 Particle in Cell 模擬 .......................................................... 15
3.1.1 OSIRIS................................................................. 17
3.1.2 二維 PIC 之模擬設置 ................................................. 17
3.1.3 二維及三維 PIC 柱座標模擬中雷射演化之差異 ...................... 18
3.2 VORPAL 與 OSIRIS 二維 PIC 模擬結果之比較 ............................ 20
3.2.1 VORPAL 和 OSIRIS 雷射參數設定之差異 ........................... 20
3.2.2 VORPAL 和 OSIRIS 在衝擊波注入下之電子能譜差異 .............. 23
3.2.3 優化在二維模擬下 OSIRIS 注入電子為單能電子 .................... 23
3.3 二維模擬下電子的注入模式 .................................................. 24
3.3.1 電子的橫向注入 ....................................................... 25
3.3.2 電子的縱向注入 ....................................................... 26
3.4 傾斜衝擊波前沿之注入電子 .................................................. 27
3.4.1 橫向注入電子之單邊注入電子 ........................................ 27
3.4.2 縱向注入電子之單邊注入電子 ........................................ 28
3.5 結論 ........................................................................... 30

四、三維雷射電漿尾場之模擬設置與結論 31
4.1 三維模擬之衝擊波前沿注入電子 ............................................. 31
4.1.1 調降電漿密度降低自注入電子束...................................... 31
4.2 三維模擬之衝擊波前沿橫向注入電子 ........................................ 33
4.2.1 不同傾角注入電子之空間分佈與能譜................................. 33
4.2.2 衝擊波前沿注入之電子束能譜 ........................................ 36
4.3 三維模擬之衝擊波前沿縱向注入電子 ........................................ 37
4.3.1 調整雷射與電漿分佈參數達成縱向注入條件 ......................... 37
4.3.2 縱向注入電子束之能譜................................................ 40
4.3.3 不同傾角注入電子之單邊注入率與能譜 .............................. 41
4.4 結論 ........................................................................... 42

五、雷射電漿尾場加速之輻射效應 43
5.1 注入電子束橫向震盪強度分析................................................ 43
5.1.1 橫向注入電子束群體運動行為 ........................................ 44
5.1.2 縱向注入電子束群體運動行為 ........................................ 45
5.2 X-ray 光通量及極化率分析 ................................................... 47
5.2.1 橫向及縱向注入在 65◦ 偏振度隨時間之演化 ......................... 50
5.3 X-ray 亮度及頻譜分析 ........................................................ 57
5.3.1 角光譜強度之計算方法................................................ 57
5.3.2 橫向注入電子束之角光譜強度 ........................................ 60
5.4 X-ray 之計算方法 ............................................................. 62
5.4.1 Betatron 脈衝時間計算................................................ 63
5.4.2 Betatron 源面積計算 .................................................. 66
5.4.3 縱向注入電子束產生 X-ray 之亮度 ................................... 67
5.5 結論 ........................................................................... 67

六、總結 69
6.1 結論 ........................................................................... 69
6.2 未來展望 ...................................................................... 69

參考文獻 71

附錄 A 圖片及程式連結 75
A.1 圖片儲存連結 ................................................................. 75
A.2 程式儲存連結 ................................................................. 82

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指導教授

周紹暐(Shao-Wei Chou)

審核日期

2024-9-30

推文