Advanced characterization and control of laser wakefield acceleration [Elektronische Ressource] / Alexander Buck. Betreuer: Ferenc Krausz

Alexander Buck

Sujets

• Physik

Informations

• Publié par: ludwig-maximilians-universitat_munchen
• Publié le: 01 janvier 2011
• Nombre de lectures: 37
• Langue: English
• Poids de l'ouvrage: 6 Mo

Extrait

Advanced characterization and
control of laser wakefield acceleration
Alexander Buck
München2011Advanced characterization and
control of laser wakefield acceleration
Alexander Buck
Dissertation
an der Fakultät für Physik
der Ludwig–Maximilians–Universität
München
vorgelegt von
Alexander Buck
aus Stuttgart
München, den 22. Juli 2011Erstgutachter: Prof. Dr. Ferenc Krausz
Zweitgutachter: Prof. Dr. Toshiki Tajima
Tag der mündlichen Prüfung: 12. September 2011Contents
Contents v
List of Figures ix
List of Tables xi
Abstract xiii
Introduction 1
List of publications by the author incorporated in this thesis . . . . . . . . . . . 5
1 Theoretical foundations of high-intensity laser-plasma interaction 7
1.1 Attributes of light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.2 Laser pulse interaction with single electrons . . . . . . . . . . . . . . . . 9
1.3 Laser pulse with single atoms and ionization mechanisms . . . 11
1.4 Non-relativistic, cold, collisionless plasmas . . . . . . . . . . . . . . . . 13
1.5 Laser propagation in underdense . . . . . . . . . . . . . . . . . 14
1.6 Excitation of large-amplitude Langmuir waves . . . . . . . . . . . . . . . 20
1.7 Maximum attainable field and longitudinal wave breaking . . . . . . . . . 24
1.8 Limiting factors for the acceleration of electrons . . . . . . . . . . . . . . 28
1.9 Optimum acceleration conditions and scaling laws . . . . . . . . . . . . . 31
1.10 Injection of electrons into wakefields . . . . . . . . . . . . . . . . . . . . 33
1.10.1 Self-injection via transverse wave breaking . . . . . . . . . . . . 34
1.10.2 Injection at plasma density transitions . . . . . . . . . . . . . . . 36
1.10.3 Colliding pulse injection . . . . . . . . . . . . . . . . . . . . . . 37
1.10.4 Ionization injection . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.11 Particle-in-cell simulations (PIC) . . . . . . . . . . . . . . . . . . . . . . 39vi CONTENTS
2 Basic experimental setup 43
2.1 Laser systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.1.1 Light Wave Synthesizer 20 (LWS-20) . . . . . . . . . . . . . . . 43
2.1.2 Advanced Titanium-Sapphire Laser (ATLAS) . . . . . . . . . . . 48
2.2 Gas targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
2.2.1 Subsonic and supersonic nozzles . . . . . . . . . . . . . . . . . . 48
2.2.2 Gas flow characterization . . . . . . . . . . . . . . . . . . . . . . 49
2.2.3 Shocks in supersonic flows . . . . . . . . . . . . . . . . . . . . . 51
2.3 Electron detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.3.1 Energy-independent charge measurements . . . . . . . . . . . . . 53
2.3.2 Electron energy spectrometer . . . . . . . . . . . . . . . . . . . 55
2.3.3 Absolute charge calibration of scintillating screens . . . . . . . . 57
2.3.4 Pointing monitor . . . . . . . . . . . . . . . . . . . . . . . . . . 63
2.3.5 Advanced diagnostics . . . . . . . . . . . . . . . . . . . . . . . 63
3 Controlled injection of electrons into wakefields 65
3.1 LWFA with LWS-20 in the self-injection regime . . . . . . . . . . . . . . 65
3.2 Controlled injection at sharp density transitions with LWS-20 . . . . . . . 69
3.2.1 Stable electron runs with tunable energy . . . . . . . . . . . . . . 69
3.2.2 Measuring the longitudinal field and dephasing eects . . . . . . 73
3.2.3 Observation of beamloading . . . . . . . . . . . . . . . . . . . . 74
3.2.4 Scaling with the background electron density . . . . . . . . . . . 76
3.3 Controlled injection with ATLAS . . . . . . . . . . . . . . . . . . . . . . 77
3.3.1 Stable injection . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.3.2 Tunability over a wide range . . . . . . . . . . . . . . . . . . . . 80
4 Real-time observation of laser-driven electron acceleration 83
4.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4.2 Experimental setup and simulation results . . . . . . . . . . . . . . . . . 85
4.2.1 Basic setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.2.2 Simulation of the signal via ray-tracing . . . . . . . . . . . . . . 85
4.3 Electron bunch measurements via Faraday rotation . . . . . . . . . . . . 89
4.4 Plasma wave via shadowgraphy . . . . . . . . . . . . . . . 92
4.5 Snapshots of LWFA via the combination of polarimetry and shadowgraphy 95
5 Conclusions 99
6 Outlook 103CONTENTS vii
A Cross-Polarized Wave Generation (XPW) 107
Bibliography 113
Publications by the Author 129
Data archiving 131
Curriculum Vitae 139
Acknowledgements 143viii CONTENTSList of Figures
1.1 Comparison of dierent ionization mechanisms . . . . . . . . . . . . . . 12
1.2 Refraction of a probe beam at the plasma . . . . . . . . . . . . . . . . . 17
1.3 Snell’s law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.4 Nonlinear, one-dimensional wakefield . . . . . . . . . . . . . . . . . . . 23
1.5 Optimum wakefield driving conditions . . . . . . . . . . . . . . . . . . . 25
1.6 Longitudinal phase-space in the one-dimensional model . . . . . . . . . . 27
1.7 Comparison of dephasing and depletion length . . . . . . . . . . . . . . . 29
1.8 Illustration of the beamloading eect . . . . . . . . . . . . . . . . . . . . 31
1.9 Transverse wave breaking in the "bubble" regime . . . . . . . . . . . . . 35
1.10 Injection of electrons at a sharp density transition. . . . . . . . . . . . . . 38
1.11 Particle-in-cell simulation . . . . . . . . . . . . . . . . . . . . . . . . . . 41
2.1 Basic experimental setup for LWFA experiments . . . . . . . . . . . . . 44
2.2 Layout of Light Wave Synthesizer 20 . . . . . . . . . . . . . . . . . . . 45
2.3 Output parameters of LWS-20 . . . . . . . . . . . . . . . . . . . . . . . 46
2.4 Layout of the ATLAS laser system . . . . . . . . . . . . . . . . . . . . . 47
2.5 Gas jet interferometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
2.6 Gaussian and trapezoidal fit functions . . . . . . . . . . . . . . . . . . . 50
2.7 Comparison of fitting routine and Abel inversion . . . . . . . . . . . . . 52
2.8 Generation of a shockfront in a supersonic flow . . . . . . . . . . . . . . 54
2.9 Electron energy spectrometer . . . . . . . . . . . . . . . . . . . . . . . . 56
2.10 Setup for the calibration of the scintillating screens . . . . . . . . . . . . 58
2.11 Emission spectrum, quantum eciency, and modulation transfer function 59
2.12 Absolute calibration of scintillating screens . . . . . . . . . . . . . . . . 61
2.13 Saturation of scintillating screens . . . . . . . . . . . . . . . . . . . . . . 62
3.1 High energy series of self-injected electrons with LWS-20 . . . . . . . . 66
3.2 Stable series of self-injected electrons with LWS-20 . . . . . . . . . . . . 67
3.3 Two stable electron series injected at the density transition with LWS-20 . 70x List of Figures
3.4 Comparison of self-injection and density transition injection with LWS-20 72
3.5 Accelerating field and dephasing of the electron bunch . . . . . . . . . . 75
3.6 Observation of beamloading . . . . . . . . . . . . . . . . . . . . . . . . 76
3.7 Scaling of the electron energy with the electron density . . . . . . . . . . 78
3.8 Comparison of self-injection and density transition injection with ATLAS 79
3.9 Tunability of LWFA with ATLAS and density transition injection . . . . . 80
3.10 Energy dependence of beam parameters and accelerating field . . . . . . 82
4.1 Illustration of laser wakefield acceleration . . . . . . . . . . . . . . . . . 84
4.2 Setup for Faraday rotation and shadowgraphy experiments. . . . . . . . . 86
4.3 Simulation of the polarimetry and shadowgraphy signal. . . . . . . . . . 88
4.4 Raw images and evaluated polarization rotation angle . . . . . . . . . . . 90
4.5 Scaled polarization rotation angle vs. charge . . . . . . . . . . . . . . . . 92
4.6 Plasma wave observation via shadowgraphy. . . . . . . . . . . . . . . . . 93
4.7 Shadowgram of the shockfront . . . . . . . . . . . . . . . . . . . . . . . 94
4.8 Snapshots of the trapped electrons and the plasma wave. . . . . . . . . . 96
4.9 Evolution of the electron bunch duration and the plasma wave during the
acceleration process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
6.1 Overview over the main beam parameters of all stable runs with ATLAS . 104
6.2 Evolution of the electron bunch during the acceleration process
with controlled injection. . . . . . . . . . . . . . . . . . . . . . . . . . . 106
A.1 Cross-polarized wave generation setup . . . . . . . . . . . . . . . . . . . 109
A.2 Contrast enhancement of LWS-20 with XPW . . . . . . . . . . . . . . . 110
A.3 Spectral broadening by cross-polarized wave generation . . . . . . . . . . 112