Fritzler, Sven (2003) Particules sources with high-intensity lasers: A tool for plasma diagnostics and an inovative source for applications. PhD thesis LOA, ENSTA / EP / LOA - Laboratoire d'Optique Appliquée UMR 7639, EP/X p.179.

Alternative Locations: http://www.imprimerie.polytechnique.fr/Theses/Files/doktor_arbeit.pdf

Abstract

This PhD dissertation is an experimental and theoretical study of particle generation by relativistic laser plasma interactions. In the first part of this manuscript, different mechanisms for neutron, electron as well as proton generation are presented and discussed for underdense and overdense plasmas. The second part is devoted to neutron generation by D(d,n)3He reactions as a diagnostic for the plasma ion temperature. The generation of an electron beam generated in the newly described "forced laser wakefield" regime is the issue for the third part. It is shown experimentally as well as theoretically that the utilization of a compact laser can result in an energetic and high quality electron beam. The last part shows that the same laser system can be implemented to generate a proton beam and that different acceleration mechanisms can yield in a proton beam. For any of the described particles several applications for accelerator physics, medical physics and the generation of secondary X rays will be discussed.

Table of content

Contents

1 Introduction 1

1.1 Scientific Context of Particle Production with High Intensity Lasers - 1

1.2 Objectives of Thesis - 3

1.3 Thesis Outline - 3

Part I: Theoretical Basics 5

2 Particle Acceleration Mechanisms 7

2.1 Elementary Definitions - 7

2.1.1 Laser Parameters - 7

2.1.2 Plasma Parameters - 10

2.2 Underdense Plasma - 14

2.2.1 Nonlinear Optics Phenomena - 15

2.2.2 Plasma Wave Growth Rates - 20

2.2.3 Wavebreaking – Electron Beam Generation - 22

2.2.4 Coulomb Explosion – Ion Beam Generation - 26

2.3 Overdense Plasma - 28

2.3.1 ~v £ ~B Heating – Electron Beam Generation - 28

2.3.2 Electrostatic Field – Proton Beam Generation - 30

Part II: Neutrons as a Diagnostic for Plasma Ion Temperature 35

3 Methodological Basics 37

3.1 Implications of Fusion Neutron Generation - 37

3.2 Previous Work and Motivation - 38

3.3 D(dn)3He Reaction - 39

i

3.3.1 Kinematics - 40

3.3.2 Cross Sections and Neutron Yield - 43

3.4 Summary and Discussion - 44

4 Experimental Set-up 47

4.1 VULCAN Laser System - 47

4.2 Diagnostics - 49

4.2.1 Gas Jet and Optical Diagnostics - 50

4.2.2 Deuteron Detectors - 51

4.2.3 Neutron Detectors - 53

5 Experimental Results 59

5.1 Gas Jet Interaction - 59

5.1.1 Neutron Energies - 59

5.1.2 Plasma Ion Temperature - 61

5.1.3 Neutron Yield - 62

5.2 Beam Target Interaction - 63

5.2.1 Deuteron Measurements - 63

5.2.2 Secondary CD2 Target - 65

6 Discussion 69

Part III: Electron Beam Generation in the FLWF Regime 71

7 Experimental Layout 73

7.1 Previous Experiments and Motivation - 73

7.2 Experimental Parameters - 75

7.2.1 “Salle Jaune” Laser and Optical Diagnostic - 75

7.2.2 Initial Plasma Electron Density - 76

7.3 Electron Beam Diagnostics - 77

7.3.1 Electron Spectrometer - 77

7.3.2 Integrating Current Transformer - 79

ii

7.3.3 Radiochromic Film and Copper Stack - 79

7.3.4 Nuclear Activation Diagnostic - 81

7.3.5 Emittance Diagnostics - 83

8 Experimental Results and Simulations 89

8.1 Electron Spectra and Yield - 89

8.1.1 Experimental Result - 89

8.1.2 Comparison with 3D PIC Simulation - 90

8.2 Transmitted Laser Beam - 93

8.3 Electron Angular Divergence - 94

8.3.1 Measurement with RCF and Copper Stack - 94

8.3.2 Activation Measurement - 95

8.4 Emittance - 95

8.4.1 Measurement with Pepper-Pot Diagnostic - 96

8.4.2 Comparison with Numerical Modelling - 96

8.5 Bunch Length Calculations - 97

9 Forced Laser Wakefield Regime 99

10 Applications and Conclusions 101

10.1 Electron Source - 101

10.1.1 Injector for Conventional Accelerators - 101

10.1.2 Ultra Fast Radiation Chemistry - 103

10.2 Feasibility as X-Ray Source - 107

10.2.1 Channelling Radiation - 107

10.2.2 Thomson Scattering - 110

Part IV: Proton Beam Generation with Foil Targets 112

11 Motivation and Experimental Layout 115

11.1 Previous Work and Motivation - 115

11.2 Experimental Layout - 116

11.2.1 Laser Parameters and Targets - 117

11.2.2 Proton Detector - 117

iii

12 Experimental and Numerical Results 121

12.1 Irradiation at Normal Incidence - 121

12.1.1 Experimental Results and Discussion - 121

12.1.2 Numerical Modelling - 123

12.2 Irradiation under 45± - 125

12.2.1 6 1m Plastic Foil - 125

12.2.2 13 1m Plastic Foil - 127

13 Applications 131

13.1 Positron Emission Tomography - 131

13.1.1 Principle and Requirements - 131

13.1.2 Benefits using High Repetition Rate Laser Systems - 132

13.1.3 Expected Activities - 132

13.2 Proton Beams as Radiographic Source - 134

13.2.1 Interest in Probing Laser Plasma Interactions - 134

13.2.2 Experiment and Results - 134

14 Conclusions and Perspectives 139

14.1 Conclusions - 139

14.1.1 Neutrons as a Diagnostic for Plasma Ion Temperature - 139

14.1.2 Electron Beam Generation in the FLWF Regime - 140

14.1.3 Proton Beam Generation with Foil Targets - 141

14.2 Perspectives - 142

Annex 144

A List of Publications 145

A.1 Articles in Refereed Journals - 145

A.2 Articles in Non-Refereed Journals - 147

Bibliography 149

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