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研究生：	王志嘉 Jhih-Jia Wang
論文名稱：	Performance Enhancement of Laser Wakefield Electron Accelerators Based on Shock-Front Injection
指導教授：	朱旭新 Hsu-hsin Chu
口試委員:
學位類別：	碩士 Master
系所名稱：	理學院 - 物理學系 Department of Physics
論文出版年：	2025
畢業學年度：	113
語文別：	英文
論文頁數：	95
中文關鍵詞：	雷射尾波場加速器、震波前注入法
外文關鍵詞：	laser wakefield acceleration, shock-front injection
相關次數：	點閱：10 下載：0
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震波前注入法為一項於雷射尾波場加速器中產生高品質、單一能量電子束的前沿技術。該技術可精確控制電子注入的時機與位置，從而實現極高穩定性的單一能量輸出。
本研究於中央大學採用 100-TW 雷射進行電子加速實驗。藉由在氣體介質中置放刀片以攔截超音速氣流、形成震波前，再將強脈衝雷射聚焦於該區域，得以實現震波前注入法的電子加速。實驗中採用不同出口直徑的氣體射流噴嘴調控氣體分佈:在純氦氣實驗中，當噴嘴直徑由 3 mm 增加至 5 mm 時，電子束的單一能量峰值由 125 MeV 提升至 160 MeV，且電子電量亦由 5.2 pC 提升至 45 pC;加速梯度達 100 GeV/m，與雷射尾波場加速器的理論極限相符。此外，將氣體介質由純氦氣改為混合氣體(0.5% 氮氣與 99.5% 氦氣)後，注入機率由 20% 提升至 45%。以上結果充分驗證了震波前注入法在產生高品質、單一能量電子束方面的優勢與效能。

Shock-front injection is a promising technique for generating a high-quality, monoener- getic electron beam in laser wakefield acceleration (LWFA). It provides precise control over the injection timing and position, leading to a monoenergetic output with high stability.
In this thesis, we use the 100-TW laser at National Central University to drive the elec- tron acceleration. By blocking a supersonic gas flow with a blade, we create a shock front in the gas medium. Then, by focusing the intense laser pulse in such a medium, electron acceleration with shock front injection is achieved. We use gas jet nozzles with different outlet diameters to control the gas medium distribution. In pure helium experiments, when the nozzle diameter is increased from 3 mm to 5 mm, the electron monoenergetic peak is increased from 125 MeV to 160 MeV, and the beam charge is also increased from 5.2 pC to 45 pC. The acceleration gradient reaches 100 GeV/m, consistent with the the- oretical limit of LWFA. Furthermore, by using a mixture gas of 0.5% N2 and 99.5% He instead of pure helium, the injection probability is increased from 20% to 45%. These achievements demonstrate the advantages and effectiveness of the shock-front injection technique.

able of Contents
Introduction 1
1 Advancements in Laser-Driven Plasma Acceleration Techniques . . . . . . 1
2 Equationoflaserwakefield........................... 2 
2.1 Self-focusingandself-guiding ..................... 5
3 Injectionmechanisms.............................. 6 
3.1 Ionizationinjection........................... 7 
3.2 Self-injection .............................. 8 
3.3 Shock-frontinjection .......................... 9
Experiment setup and laser source 11
1 100-TWlaserinNationCentralUniversity.................. 11
2 Setupofexperiment .............................. 13 
2.1 Beampathoflaserandalignment................... 13 
2.2 Gastarget................................ 16 
2.3 Shock-frontgeneration ......................... 21
3 Diagnosticofelectron.............................. 22 
3.1 Electronbeamprofilemeasurement.................. 23 
3.2 Electronspectrometer ......................... 25 
3.3 Chargecalibrationoftheelectronbeam . . . . . . . . . . . . . . . 28
Experiment results 29
1 Laserstatus................................... 29
2 Optimizationforshock-frontinjection..................... 33
3 Shock-FrontInjectionwithPureHeliumGas . . . . . . . . . . . . . . . . . 36
3.1 Shock-front injection with nozzle of diameter of 3 mm . . . . . . . . 37
3.2 Shock-front injection with nozzle of diameter of 5 mm . . . . . . . . 39
3.3 Shock-front injection with nozzle of diameter of 8 mm . . . . . . . . 46
3.4 Comparison of results of shock-front with pure helium gas . . . . . 48 
4 Shock-frontinjectionwithmixturegas .................... 49 
5 Listtheresults ................................. 55
Discussion and Conclusion 57
1 Discussion.................................... 57 
1.1 AccelerationLengthandDephasingLength . . . . . . . . . . . . . 57 
1.2 TheChangeofChargeinPureHelium ................ 57 
1.3 EffectsofMixtureGas(0.5%N2) ................... 58
2 Conclusion.................................... 60
Bibliography 61 A Storing path of the figures 63 B Nozzle Design 65 C 3-D diagram of the experimental setup 70
                                

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