New Type of sub-THz Oscillator and Amplifier Systems Based on Helical-Type Gyro-TWTs / / Alexander Marek.

• Superior document: Karlsruher Forschungsberichte aus dem Institut für Hochleistungsimpuls- und Mikrowellentechnik
• VerfasserIn: Marek, Alexander,
• Place / Publishing House: Karlsruhe, Baden : : KIT Scientific Publishing,, 2023.; ©2023
• Year of Publication: 2023
• Language: English
• Series: Karlsruher Forschungsberichte aus dem Institut für Hochleistungsimpuls- und Mikrowellentechnik.
• Physical Description: 1 online resource (324 pages)

This work presents the development of a new sub-THz source for the generation of trains of coherent high-power ultra-short pulses at 263 GHz via passive mode-locking of two coupled helical gyro-TWTs. For the first time, it is shown that the operation of such passive mode-locked helical gyro-TWTs in...

Table of Contents

• Foreword of the Editor i
• Zusammenfassung iii
• Abstract v
• Abbreviations xiii
• List of Symbols xvii
• 1 Introduction 1
• 1.1 Aims and Objectives 1
• 1.2 State of the Art 4
• 1.3 Method of Mode-Locking in Laser Physics 7
• 1.4 From Optics to Microwaves 13
• 1.5 Outline 14
• 2 Fundamental Theory of Passive Mode-Locked Oscillators 17
• 2.1 Characteristics of Ultra-Short Pulses 17
• 2.1.1 Slowly Varying Amplitudes 17
• 2.1.2 Ultra-Short Pulses 18
• 2.2 Haus Master Equation of Passive Mode-Locked Oscillators 20
• 2.2.1 Amplification 21
• 2.2.2 Saturable Loss and Self Amplitude Modulation 23
• 2.2.3 Dispersion 24
• .2.4 Slow Components 25
• 2.2.5 Time-Shift 27
• 2.2.6 Typical Values 28
• 2.3 Passive Mode-Locked Oscillators for MW Frequencies 30
• 2.3.1 Fast and Slow Components 30
• 2.3.2 Fast Amplifier and Fast Absorber 31
• 2.3.3 Slow Amplifier and Fast Absorber 35
• 2.4 Conclusion 37
• 3 MW Components for Passive Mode-Locked Oscillators 39
• 3.1 Helical Gyro-TWTs 39
• 3.1.1 Helically Corrugated Waveguides 41
• 3.1.2 Electron Cyclotron Maser Interaction 46
• 3.1.3 Large Orbit Electron Beams 50
• 3.1.4 CUSP-Type Electron Guns 52
• 3.1.5 Waveguide Polarizers 60
• 3.1.6 Horn Antenna and Collector 62
• 3.1.7 Broadband Windows 64
• 3.1.8 In-and Out-coupling of High-Power Signals 68
• 3.2 Cyclotron Absorber 70
• 3.3 Helical Gyro-TWTs as Saturable Absorbers 77
• 3.4 Passive Components 78
• 3.4.1 Jones Calculus 78
• 3.4.2 Polarization Splitter 81
• 3.4.3 Polarizers 84
• 4 Simulation Model for Gyro-Devices 87
• 4.1 Field Equations 89
• 4.1.1 Helically Corrugated Waveguide 91
• 4.1.2 Range of Validity 94
• 4.1.3 Multi-Mode Simulations 100
• 4.2 Equations of Motion 101
• 4.2.1 Source Term 103
• 4.2.2 Space Charge 105
• 4.3 Numerical Solution 107
• 4.3.1 Field Equations 108
• 4.3.2 Coupled Equations of Helical Waveguides 110
• 4.3.3 Source Term and Equations of Motion 111
• 4.3.4 Implementation and GPU Acceleration 112
• 4.4 Comparison with Existing Approaches 116
• 5 Design of Amplifier and Absorber 119
• 5.1 Amplifier 120
• 5.1.1 Helical Interaction Region 121
• 5.1.2 Power Capability 122
• 5.1.3 Synchronized Operation Regime 125
• 5.1.4 Slippage Operation Regime 126
• 5.1.5 Length of the Interaction Region 127
• 5.1.6 Amplification of Ultra-Short Pulses 129
• 5.2 Saturable Absorber 134
• 5.2.1 Helical Gyro-TWT Absorber 135
• 5.2.2 Cyclotron Absorber 137
• 5.2.3 Ultra-Short Pulses in a Saturable Absorber 142
• 5.3 Effects of Manufacturing Tolerances 147
• 6 System Design 151
• 6.1 Simulation of a Passive Mode-Locked Oscillator 151
• 6.2 Different Passive Mode-Locked Oscillators 153
• 6.3 Generated Output Signal 157
• 6.3.1 Pulse Power and Length 158
• 6.3.2 Pulse Shape 160
• 6.3.3 Spectrum 161
• 6.4 Transient Behavior of the Oscillator 167
• 6.4.1 Start-up in the Hard Excitation Region 167
• 6.4.2 Start-up in the Soft Excitation Region 169
• 6.4.3 Achievable Repetition Rate 171
• 6.4.4 Achievable Coherence 174
• 6.5 Realistic Start-Up Scenarios 178
• 6.5.1 High-Gain HelicalGyro-TWT 179
• 6.5.2 Hard Excitation with a High-Gain HelicalGyro-TWT 181
• 6.6 Conclusion 182
• 7 Simulation Model for Passive Components 185
• 7.1 Surface Integral Equations 186
• 7.2 Numerical Solution 188
• 7.2.1 Adaptive Cross Approximation 189
• 7.2.2 Sparsified Adaptive Cross Approximation 190
• 7.3 New Zero-Cost Preconditioner 192
• 7.3.1 GMRE Swith Preconditioner 192
• 7.3.2 FGMRE Swith Zero-Cost Preconditioner 193
• 7.3.3 Performance of the Zero-Cost Preconditioner 195
• 7.4 Implementation and Verification 200
• 7.5 Dispersion of Helically Corrugated Waveguides 203
• 8 Design of the Feedback System 205
• 8.1 Requirements 206
• 8.2 Feedback System via Overmoded Waveguides 208
• 8.2.1 Waveguide 210
• 8.2.2 Broadband Polarization Splitter 212
• 8.2.3 Broadband Polarizer 215
• 8.2.4 Performance of the Complete Feedback System 219
• 8.3 Additional Operation Modes 220
• 8.3.1 Operation in the Hard Excitation Region 222
• 8.3.2 New Type of Two-Stage Amplifier 224
• 8.3.3 Operation as a CW Source 226
• 8.4 Conclusion 229
• 9 Conclusion and Outlook 231
• A Appendix 239
• A.1 Split-Step Fourier Method 239
• A.2 Verification of Electron-Wave Interaction Simulations 240
• A.2.1 Short-Pulse ITERGyrotron 241
• A.2.2 W-Band HelicalGyro-TWT 245
• A.3 Verification of EFIE Solver 249
• A.3.1 Verification of Simulated Field Distribution 249
• A.3.2 Verification of Simulated Ohmic-Loss 252
• A.4 Passive Mode-locked Oscillator with Cyclotron Absorber 254
• Bibliography 257
• Contents Acknowledgment 281.