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 the hard excitation regime is of particular importance to reach the optimal coherency of the generated pulses. This could be of particular interest for some new time-domain DNP-NMR methods.

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.