Foreword by Dr. Delores Etter ................................ xiii
Preface .......................................................... xv
Acknowledgments ................................................ xvii
List of Contributors ............................................ xix
List of Acronyms and Abbreviations .............................. xxv
Chapter 1. INTRODUCTION ........................................... 1
1.1. Setting and Motivation ...................................... 1
1.2. High-Power Microwaves ....................................... 1
1.3. Organization and Scope of the Book .......................... 4
References ........................................................ 6
Chapter 2. HPM SOURCES: THE DOD PERSPECTIVE ....................... 7
2.1. Introduction ................................................ 7
2.2. Role of the DoD in Basic Research ........................... 8
2.3. DoD Needs .................................................. 10
2.4. History .................................................... 11
2.4.1. Air Force .......................................... 13
2.4.2. Army ............................................... 15
2.4.3. Navy ............................................... 19
2.4.4. DoD Agencies ....................................... 20
2.5. Advances in HPM Development ................................ 21
2.5.1. High-Power Narrowband Source Development ........... 23
2.5.2. High-Power Ultra-Wideband Source Development ....... 26
2.6. Enabling Technologies ...................................... 27
2.6.1. Pulsed Power ....................................... 29
2.6.2. Novel Cathodes ..................................... 29
2.6.3. Improved Materials and Breakdown Strength .......... 30
2.6.4. Antennas ........................................... 30
2.6.5. Computational Capabilities ......................... 31
2.7. Summary .................................................... 31
2.8. Acknowledgments ............................................ 32
References ....................................................... 32
Chapter 3. GIGAWATT-CLASS SOURCES ............................... 38
3.1. Introduction ............................................... 38
3.1.1. Definition of High-Power Sources ................... 39
3.1.2. Evolution and History .............................. 40
3.1.3. Issues for Increasing Power and Pulselength ........ 40
3.2. Major Gigawatt-Level HPM Sources ........................... 44
3.2.1. Magnetically Insulated Line Oscillator (MILO) ...... 44
3.2.2. Tapered MILO ....................................... 50
3.2.3. Relativistic Magnetron ............................. 56
3.2.4. Relativistic Klystron Amplifier (RKA) and
Triaxial RKA ....................................... 60
3.2.5. Relativistic Klystron Oscillator (RKO) ............. 66
3.2.6. Reltron ............................................ 69
3.3. Future Improvements and Summary ............................ 72
References ....................................................... 73
Chapter 4. PULSE SHORTENING ..................................... 77
4.1. Introduction ............................................... 77
4.2. Overview of Earlier Results ................................ 79
4.2.1. Pulse-Shortening Mechanisms ........................ 79
4.2.2. "Hard Tube" and "Soft Tube" Techniques ............. 82
4.3. Thrusts of Recent Research ................................. 88
4.3.1. Surface and Vacuum Techniques ...................... 88
4.3.2. Source Pulse-Lengthening Progress .................. 91
4.4. Summary ................................................... 111
References ...................................................... 112
Chapter 5. RELATIVISTIC CERENKOV DEVICES ....................... 116
5.1. Introduction .............................................. 116
5.2. Traveling Wave Tube Amplifiers ............................ 117
5.2.1. Introduction ...................................... 117
5.2.2. Single-Stage TWT .................................. 119
5.2.3. Two-Stage TWT ..................................... 119
5.2.4. Macro-Particle Analysis ........................... 120
5.2.5. Tapered Amplifier Design .......................... 121
5.2.6. Transit Time Isolation ............................ 122
5.3. Recent High-Power TWT Amplifier Research .................. 123
5.3.1. Introduction ...................................... 123
5.3.2. Quasi-Periodic Structures ......................... 123
5.3.3. High Efficiency Output Structures ................. 123
5.3.4. Axial Extraction .................................. 124
5.3.5. High-Efficiency Amplifier Operation ............... 126
5.3.6. Bunch Compression ................................. 128
5.3.7. Ka-Band Studies ................................... 129
5.3.8. Hybrid Modes ...................................... 130
5.3.9. Interaction of Symmetric and Asymmetric Modes ..... 131
5.3.10. Discussion ........................................ 135
5.4. Backward Wave Oscillators ................................. 136
5.4.1 Introduction ........................................ 136
5.4.2. Repetitively Pulsed Operation ..................... 136
5.4.3. Efficiency Enhancement ............................ 137
5.4.4. Millimeter-Wave BWOs .............................. 138
5.4.5. Ultra-High-Power Operation ........................ 138
5.4.6. Long-Pulse Operation .............................. 139
5.5. Recent High-Power BWO Research ............................ 139
5.5.1. Characterization of SWSs .......................... 140
5.5.2. Theory of BWOs .................................... 142
5.5.3. Experiments ....................................... 145
5.6. Acknowledgments ........................................... 149
References ...................................................... 150
Chapter 6. GYROTRON OSCILLATORS AND AMPLIFIERS ................. 155
6.1. Introduction .............................................. 155
6.1.1. Chapter Outline ................................... 155
6.1.2. The Gyrotron Concept .............................. 157
6.2. The State-Of-The-Art in High-Power Gyrotrons .............. 160
6.2.1. Gyromonotron Oscillators for Plasma Heating and
Current Drive ..................................... 160
6.2.2. Gyrotrons Driven by Intense Relativistic
Electron Beams (IREBs) ............................ 162
6.2.3. Gyro-Amplifiers for Millimeter Wave Radar ......... 163
6.2.4. Gyro-BWOs for Millimeter Wave ECM ................. 166
6.2.5. Gyromonotron Oscillators for Industrial
Applications ...................................... 168
6.2.6. Gyroklystron Amplifiers for Driving
Accelerators ...................................... 169
6.3. Recent Progress in Gyrotrons Driven by IREBs .............. 170
6.3.1. IREBs, Gyro-Devices, and Space-Charge
Considerations .................................... 170
6.3.2. Rectangular and Coaxial Gyrotrons ................. 171
6.3.3. Evaluation of Gyro-BWOs as Broadly Tunable HPM
Sources ........................................... 174
6.4. Frequency Multiplying Gyro-Amplifiers for Advanced
Radars .................................................... 176
6.4.1. Theory ............................................ 178
6.4.2. Experiment ........................................ 182
6.5 High-Harmonic Operation of Gyrotrons with Axis-Encircling
Beams ....................................................... 185
6.5.1. High-Harmonic Gyrotron Oscillators ................ 186
6.5.2. Harmonic Gyrotron Amplifiers ...................... 188
6.6. Summary ................................................... 189
6.7. Acknowledgments ........................................... 190
References ...................................................... 191
Chapter 7. ACTIVE PLASMA LOADING OF HPM DEVICES ................ 199
7.1. Introduction .............................................. 199
7.2. Overview of Earlier Results ............................... 200
7.2.1. Historical Perspective ............................ 200
7.2.2. Theory ............................................ 202
7.2.3. Experiments ....................................... 205
7.3. Recent Advances in Plasma-Filled HPM Sources .............. 212
7.3.1. Experimental Results .............................. 212
7.3.2. Theoretical and Simulation Results ................ 220
7.3.3. Plasma Generation Techniques ...................... 230
7.3.4. Novel Diagnostic Techniques ....................... 233
7.3.5. Electromagnetic Properties of SWSs Loaded with
Radially Inhomogeneous Plasma ..................... 237
7.3.6. Most Important Experimental and Theoretical
Results ........................................... 241
7.4. Summary and Open Issues ................................... 244
7.5. Acknowledgments ........................................... 244
References ................................................ 245
Chapter 8. BEAM TRANSPORT AND RF CONTROL ....................... 250
8.1. Introduction .............................................. 250
8.2. Beam Transport ............................................ 252
8.2.1. Overview .......................................... 252
8.2.2. Magnetic Guide-Field Systems ...................... 252
8.2.3. PPM Focusing of Linear Beam HPM Devices ........... 254
8.2.4. Beam Transport in Plasma-Filled Systems ........... 260
8.2.5. Magnetic Self-Insulation in the MILO .............. 265
8.2.6. Beam Transport Details Peculiar to Gyro-Devices ... 265
8.3. Electron Beam Dumps ....................................... 266
8.3.1. Conventional, Single-Stage Beam Dumps ............. 266
8.3.2. Depressed Collectors .............................. 267
8.3.3. Computer Modeling of Depressed Collectors ......... 268
8.3.4. Summary ........................................... 271
8.4. Control of RF Output ...................................... 271
8.4.1. Overview .......................................... 271
8.4.2. Polarization Control of Microwave Output .......... 271
8.4.3. Mode Converters ................................... 272
8.5. Evolution of the Smart Tube Concept ....................... 273
8.5.1. Introduction ...................................... 273
8.5.2. Early Work by Litton .............................. 273
8.5.3. Automated Control Studies at SLAC ................. 274
8.5.4. GW-Level Smart Tube ............................... 274
8.6. Summary ................................................... 280
8.7. Acknowledgments ........................................... 280
References ...................................................... 280
Chapter 9. CATHODES AND ELECTRON GUNS .......................... 284
9.1. Introduction .............................................. 284
9.2. Technology Overview ....................................... 285
9.3. Cathode Technologies ...................................... 288
9.3.1. Explosive Emitters ................................ 288
9.3.2. Advances in Thermionic Emitters ................... 298
9.3.3. Ferroelectric Cathodes ............................ 305
9.4. Novel Electron Guns ....................................... 309
9.4.1. Plasma Electron Gun ............................... 309
9.4.2. High-Power Cusp Gun ............................... 312
9.4.3 Ferroelectric Electron Gun .......................... 316
9.5 Summary and Future Directions ............................... 318
Chapter 10. WINDOWS AND RF BREAKDOWN ............................ 325
10.l. Introduction .............................................. 325
10.2. Overview of Earlier Work .................................. 326
10.3. Basic Considerations ...................................... 328
10.3.1. Physical Mechanisms ............................... 328
10.3.2. Unipolar Surface Breakdown ........................ 333
10.4. Multipactor Theory ........................................ 334
10.4.1. Two-Surface Multipactor on Metals ................. 335
10.4.2. Single-Surface Multipactor on Dielectrics ......... 338
10.4.3. Further Discussion ................................ 341
10.5. Breakdown in RF Structures ................................ 346
10.5.1. TM010 Cavity in an X-Band Ring .................... 347
10.5.2. TM020 Cavity ...................................... 348
10.5.3. Discussion ........................................ 355
10.6. Dielectric Window Breakdown ............................... 356
10.6.1. Experimental Approach ............................. 356
10.6.2. Experimental Results .............................. 358
10.6.3. Further Discussion ................................ 362
10.7. Methods of Breakdown Suppression .......................... 365
10.8. Summary ................................................... 368
10.9. Acknowledgments ........................................... 369
References ...................................................... 370
Chapter 11. COMPUTATIONAL TECHNIQUES ............................ 376
11.1. Introduction .............................................. 376
11.2. Overview of the PIC Method ................................ 377
11.2.1. Field Equations ................................... 379
11.2.2. Field Boundary Conditions ......................... 380
11.2.3. Particle Equations ................................ 383
11.2.4. Particle Boundary Conditions ...................... 384
11.2.5. Coupling Fields and Particles ..................... 385
11.3 Modeling HPM Sources Using PIC Simulation: A Tutorial
11.4. Recent Advances in PIC .................................... 391
11.4.1. Plasma Model ...................................... 391
11.4.2. Secondary Emission ................................ 397
11.4.3. Charge Conservation in Electromagnetic PIC Codes
11.4.4. Modal Expansion PIC ............................... 406
11.4.5. Poynting Splitter ................................. 407
11.4.6. Object-Oriented Techniques ........................ 409
11.4.7. Parallel PIC Codes ................................ 411
11.4.8. Conclusion ........................................ 419
11.5. Overview of Parametric Modeling ........................... 419
11.6. Recent Advances in Parametric Modeling .................... 424
11.6.1. MAGY .............................................. 424
11.6.2. Gap-Circuit Models ................................ 426
11.7. Summary and Future Issues ................................ 430
11.7.1. Body-Fitted Coordinates ........................... 431
11.7.2. Probabilistic Surface Physics ..................... 431
11.7.3. Hybrid Software ................................... 431
11.7.4. Parallel Checkpointing ............................ 432
11.7.5. Data Visualization ................................ 432
References ...................................................... 432
Chapter 12. ALTERNATIVE APPROACHES AND FUTURE CHALLENGES ........ 438
12.1. Introduction .............................................. 438
12.2. Remaining Research Challenges ............................. 439
12.2.1. Cleanliness and High Vacuum for HPM Devices........ 439
12.2.2. Novel Cathodes and Electron Guns .................. 441
12.2.3. Improved Breakdown Prevention for HPM Surfaces
and Windows ....................................... 444
12.2.4. Pulsed Power ...................................... 447
12.2.5. Modeling and Computational Techniques ............. 448
12.2.6. Advanced Diagnostics .............................. 450
12.2.7. Recirculation of Spent Beam Energy ................ 451
12.2.8. Smart, Adaptive HPM Devices ....................... 451
12.2.9. Detuning Incorrectly Phased Electrons ............. 452
12.2.10.Corona Onset Mitigation ........................... 455
12.2.11.Mode Converters ................................... 455
12.2.12.Use of Permanent Magnet Focusing .................. 456
12.3. Alternative HPM Source Concepts ........................... 457
12.3.1. Ganged Arrays of Moderate Power Devices ........... 457
12.3.2. The Gigawatt Multiple-Beam Klystron (GMBK) ........ 453
12.3.3. Sheet Beam HPM Sources ............................ 463
12.3.4. Future Relativistic Čerenkov Devices .............. 464
12.3.5. New Vircator Configurations ....................... 465
12.3.6. The Plasma Electron Microwave System (PEMS)
Concept ........................................... 467
12.3.7. Klystrinos: W-Band Modular Klystrons .............. 469
References ...................................................... 471
INDEX ........................................................... 477
ABOUT THE EDITORS ............................................... 485
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