Investigations on rf breakdown phenomenon in high gradient accelerating structures (eBook)

Jiahang Shao received his Bachelor’s degree in Engineering from the Department of Electronic Engineering at Tsinghua University, China in 2011. He obtained his Ph.D. in Engineering from the Department of Engineering Physics at the same university in July 2016, where his major research project in Prof. Huaibi Chen’s group was the experimental study of rf breakdown and field emission in high gradient accelerating structures. Currently, he is a postdoctoral appointee working with Prof. Wei Gai at Argonne National Laboratory, USA, continuing his study on field emission and conducting research on wakefield generation by intense electron beam.

Supervisor’s Foreword 7
Preface 8
Acknowledgements 10
Contents 12
1 Introduction 1
1.1 Application of High Gradient Accelerating Structures 14
1.1.1 Compact Electron-Positron Collider 15
1.1.2 Compact Light Source 16
1.1.3 Photocathode rf Gun 17
1.1.4 Industry/Medical Accelerator 18
1.2 rf Breakdown 19
1.2.1 Phenomenon 20
1.2.2 Impact 21
1.2.3 Research Status 23
1.3 Field Emission 30
1.3.1 Phenomenon 30
1.3.2 Research Status 32
1.4 Main Content and Innovation 35
References 37
2 Experimental Research of Laser-Triggered rf Breakdown 1
2.1 Physical Background 42
2.2 Experimental Setup 43
2.2.1 S-Band Photocathode rf Gun 43
2.2.2 Diagnostics 44
2.3 Experiment Observation 45
2.3.1 Surface Damage Test 45
2.3.2 High Power Test 47
2.4 Basic Analysis 51
2.4.1 Modes Evolution 51
2.4.2 Frequency Detuning 56
2.4.3 Time Structure of rf Breakdown Current 56
2.5 Advanced Analysis with an Equivalent Circuit Model 58
2.5.1 Equivalent Circuit Model 58
2.5.2 Basic Equations 59
2.5.3 Parameters 63
2.5.4 Analysis 65
2.5.5 Discussion 67
2.6 Summary 70
References 70
3 Experimental Research of Pin Cathode 72
3.1 L-Band Photocathode rf Gun Test Stand 72
3.1.1 L-Band Photocathode rf Gun 72
3.1.2 Test Stand 77
3.2 Evolution of Field Emission During rf Conditioning 79
3.2.1 rf Conditioning of Pin Cathodes 80
3.2.2 Field Emission Measurement 82
3.2.3 Surface Examination 85
3.2.4 Discussion 86
3.3 Field Emission Dependence on Stored Energy 88
3.3.1 Field Emission Current Measurement 88
3.3.2 Dynamics of Field Emission Current 92
3.3.3 Possible Mechanisms 97
3.3.4 Discussion 102
3.4 Summary 103
References 103
4 In-situ High Resolution Field Emission Imaging 106
4.1 Imaging Method 106
4.1.1 Difficulties 106
4.1.2 Solution 108
4.2 Dynamics Simulation 110
4.2.1 Imaging Properties 110
4.2.2 Electron Distribution 112
4.2.3 Emission Phase Selection 112
4.2.4 Beam Line Optimization 114
4.3 Experiment Preparation 122
4.3.1 New Cathode 122
4.3.2 Beam Line Upgrading 123
4.4 High Resolution Field Emission Imaging Experiment 126
4.4.1 In-situ High Resolution Field Emitter Observation 127
4.4.2 Field Enhancement Factor Measurement 129
4.4.3 Surface Analysis 133
4.5 Summary 135
References 135
5 Summary and Future Study 137
Appendix A Calculating the Electric Field on the Pin Cathode 140