Klystrons, Traveling Wave Tubes, Magnetrons, Crossed-Field Amplifiers, and Gyrotrons

12 Pages·2011·3.2 MB·English

Klystrons,
Traveling Wave Tubes,
Magnetrons,
Crossed-Field Amplifiers,
and Gyrotrons
A. S. Gilmour, Jr.
ARTECH
H O U SE
BOSTON|LONDON
artechhouse.com
Contents
PREFACE xvii
CHAPTER 1 INTRODUCTION 1
1.1 The Microwave Spectrum 1
1.2 The Domain of Microwave Tubes 2
1.3 Classical Microwave Tube Types 3
1.4 Overview of This Book 8
References 9
CHAPTER 2 STATIC FIELDS PRODUCED BY ELECTRONS 11
2.1 Electric Field 11
2.2 Magnetic Field 17
CHAPTER 3 ELECTRON MOTION IN STATIC ELECTRIC FIELDS 19
3.1 Motion Parallel to Field 19
3.2 Relativistic Velocity Corrections 20
3.3 Electric Lenses 22
3.4 Universal Beam Spread Curve 26
CHAPTER 4 INFLUENCE OF MAGNETIC FIELD ON ELECTRON
MOTION 31
4.1 Electron Motion in a Static Magnetic Field 31
4.2 Electron Motion in Combined Electric and Magnetic Fields 33
4.2.1 Perpendicular Fields in Rectangular Coordinates 33
4.2.2 Axially Symmetric Fields 35
CHAPTER 5 THERMIONIC CATHODES 39
5.1 Emission Mechanisms 41
5.1.1 Thermionic Emission 41
5.1.2 Schottky Effect 45
5.1.3 Field Emission 47
5.1.4 Space Charge Limitation 49
5.2 Evolution of Thermionic Cathodes 54
V
vi Klystrons, TWTs, Magnetrons, Crossed-Field Amplifiers, and Gyrotrons
5.3 Impregnated Dispenser Cathodes 60
5.3.1 Fabrication 60
5.3.2 Operation 63
5.3.3 Miram Curves 63
5.3.4 Work Function Distribution 65
5.4 Life Considerations 70
5.4.1 Grant and Falce Life Prediction Model 74
5.4.2 Longo Life Prediction Model 76
5.5 Dispenser Cathode Surface Physics 79
5.6 Heaters 85
5.6.1 Conventional Heater Assemblies 85
5.6.2 Fast Warm-Up Heaters 88
5.6.3 Heater Testing 89
5.6.4 Effect of Filament Magnetic Field 90
References 92
CHAPTER 6 ELECTRON GUNS 95
6.1 Pierce Guns 95
6.1.1 Focus Electrodes for Parallel Flow 96
6.1.2 Focus Electrodes for Convergent Flow 98
6.1.3 Defocusing Effect of Anode Aperture 103
6.1.4 Formation of Minimum Beam Diameter 107
6.1.5 Thermal Velocity Effects 109
6.1.6 Effects of Patchy Emission and Cathode Roughness 113
6.2 Beam Control Techniques 114
6.2.1 Cathode Pulsing 114
6.2.2 Control Focus Electrodes 114
6.2.3 Modulating Anode 116
6.2.4 Grids " 116
6.2.5 Summary of Beam Control Electrode Characteristics 128
References 130
CHAPTER 7 ELECTRON BEAMS 133
7.1 Overview of Uniform-Field Focusing 134
7.1.1 Brillouin Flow 135
7.1.2 Scalloping 136
7.1.3 Confined (Immersed) Flow 140
7.2 Uniform-Field Focusing and Laminar Flow 142
7.2.1 The Beam Equation 142
7.2.2 Brillouin Flow 145
7.2.3 Confined (Immersed) Flow 149
7.3 Uniform-Field Focusing and Nonlaminar Flow 153
Contents VII
7.4 Focusing with Permanent Magnets 155
7.4.1 Overview 155
7.4.2 Laminar Flow, No Cathode Flux 157
7.4.3 Laminar Flow with Cathode Flux 163
7.4.4 Nonlaminar Flow 167
7.5 Ion Effects in Electron Beams 173
7.5.1 Examples of Ion Effects 174
7.5.2 Gas Sources 178
7.5.3 Ionization 180
7.5.4 Potential Depression in an Electron Beam 182
7.5.5 Steady State Effects of Ionization 185
7.5.6 Low-Frequency Instabilities 189
7.5.7 High-Frequency Instabilities 192
References 197
CHAPTER 8 BEAM-GAP INTERACTIONS 201
8.1 Beam Modulation 201
8.1.1 Gridded (Planar) Gaps 202
8.1.2 Gridless (Nonplanar) Gaps 204
8.2 Current Induction 206
8.2.1 Gridded (Planar) Gaps 206
8.2.2 Gridless (Nonplanar) Gaps 214
8.3 Beam Loading 214
References 216
CHAPTER 9 ELECTRON BUNCHING PRODUCED BY A GAP 217
9.1 Ballistic Bunching 217
9.2 Bunching with Space Charge Forces 220
9.3 Large Signal Levels 228
References 235
CHAPTER 10 BASIC KLYSTRONS AND THEIR OPERATION 237
10.1 The Invention and Basic Operation of the Klystron 239
10.2 Klystron Cavities 244
10.2.1 Cavity Operation 244
10.2.2 Power Coupling 246
10.2.3 Tuners 248
10.2.4 Equivalent Circuits and Circuit Parameters 249
10.2.5 RF Cavity Losses 253
10.3 Small Signal Operation 254
10.3.1 Load Representation 256
10.3.2 Gain Calculation 256
viii Klystrons, TWTs, Magnetrons, Crossed-Field Amplifiers, and Gyrotrons
10.4 Power Output Characteristics 260
10.4.1 Tuning of Conventional Klystrons 261
10.4.2 Transfer Characteristics 265
References 267
CHAPTER 11 SPECIAL-PURPOSE KLYSTRONS 269
11.1 High-Efficiency Klystrons 269
11.2 High-Power Klystrons 273
11.2.1 Limits on Beam Voltage 275
11.2.2 Limits on Beam Current 277
11.2.3 Estimate of Obtainable Power 278
11.3 Broadband Klystrons 281
11.3.1 Driver Sections 283
11.3.2 Output Sections 289
11.4 Multiple Beam Klystrons 294
11.5 Extended Interaction Klystrons 304
11.6 Reflex Klystrons 311
References 313
CHAPTER 12 TRAVELING WAVE TUBES 317
12.1 Introduction 317
12.1.1 Early History of the TWT 317
12.1.2 Basic Operation of the TWT 321
12.2 Traveling Wave Interaction 325
12.2.1 RF Current in a Beam 326
12.2.2 Circuit Equation 327
12.2.3 The Determinantal Equation 328
12.2.4 Synchronous Operation 328
12.2.5 Nonsynchronous Operation 331
12.2.6 Effect of Circuit Loss 332
12.2.7 Effect of Space Charge 332
12.3 High-Level Interaction 335
12.3.1 Discussion of Interactions 335
12.3.2 Estimates of Maximum Efficiency 338
12.3.3 Comment on Computer Modeling 339
12.3.4 Velocity Tapering 340
References 344
CHAPTER 13 WAVE VELOCITIES AND DISPERSION 347
13.1 Group and Phase Velocity 347
13.2 Dispersion 349
13.2.1 Coaxial Transmission Line 350
Contents ix
13.2.2 Rectangular Waveguide 350
13.2.3 Periodically Loaded Waveguide 358
CHAPTER 14 HELIX TWTS 363
14.1 Bandwidth 363
14.1.1 Dispersion 366
14.1.2 Dispersion Control 367
14.2 Gain 371
14.2.1 Transitions 372
14.2.2 Attenuators and Severs 375
14.3 Power 377
14.3.1 Peak Power 378
14.3.2 Average Power 383
14.4 Efficiency 389
14.5 Dual-Mode Operation 394
14.6 Microwave Power Modules 396
14.7 Ring Bar and Ring Loop TWTs 398
References 402
CHAPTER 15 COUPLED-CAVITY TWTS 405
15.1 Basic Operating Principles 406
15.2 Coupled-Cavity Structures 408
15.2.1 Waveguide Approach 408
15.2.2 Curnow-Gittins Equivalent Circuit Approach 412
15.2.3 Example of an Application of the Curnow-Gittins Circuit 415
15.3 Fundamental Backward Wave Operation 421
15.4 Fundamental Forward Wave Operation 429
15.5 Terminations and Transitions 430
References 435
CHAPTER 16 COLLECTORS 437
16.1 Power Dissipation 437
16.2 Power Recovery 441
16.2.1 Power Flow 441
16.2.2 Power Recovery with a Depressed Collector 444
16.2.3 Electron Energy Distribution 447
16.2.4 Spent Beam Power 450
16.2.5 Effect of Body Current 451
16.2.6 Multistage Depressed Collectors 453
16.2.7 Secondary Electrons in Depressed Collectors 458
16.3 Collector Cooling 462
16.3.1 Conduction Cooling 462
x Klystrons, TWTs, Magnetrons, Crossed-Field Amplifiers, and Gyrotrons
16.3.2 Convection Cooling 462
16.3.3 Forced-Air Cooling 462
16.3.4 Forced-Flow Liquid Cooling 462
16.3.5 Vapor Phase Cooling 464
16.3.6 Radiation Cooling 465
References 467
CHAPTER 17 CROSSED-FIELD TUBES 469
17.1 Basic Configuration of Crossed-Field Tubes 470
17.2 Electron Flow with No RF Fields 471
Reference 475
CHAPTER 18 CATHODES FOR CROSSED-FIELD TUBES 477
18.1 Introduction 477
18.2 Characteristics of Secondary Emission 478
18.2.1 Energy of Impacting Primary Electrons 479
18.2.2 Angle of Incidence of Primary Electrons 480
18.2.3 Secondary Emitting Properties of Surfaces 481
18.2.4 Energy Distribution of Secondary Electrons 484
18.2.5 Modeling of Secondary Emission Characteristics 485
18.3 Operation of Cathodes in Crossed-Field Devices 486
References 487
CHAPTER 19 MAGNETRONS 489
19.1 Types of Magnetrons 489
19.1.1 Cyclotron-Frequency Magnetrons 489
19.1.2 Negative-Resistance Magnetrons 490
19.1.3 Traveling Wave Magnetrons 491
19.2 Operation of the Traveling Wave Magnetron 494
19.2.1 Hub Formation 494
19.2.2 The Hartree Voltage 497
19.2.3 Spoke Formation 500
19.2.4 RF Circuit Operation 504
19.3 Moding 507
19.4 Coaxial Magnetrons 513
19.5 Inverted Magnetrons 516
19.6 Magnetron Tuning 516
19.7 Output Couplers and Transformers 518
19.8 Cathode and Heater Operation 520
19.9 Performance 522
19.9.1 Voltage-Current Characteristic 522
19.9.2 Frequency Pushing 522
Contents XI
19.9.3 Frequency Pulling 523
19.9.4 Thermal Drift 525
19.10 Applications of Magnetrons 526
19.10.1 Conventional Magnetrons 526
19.10.2 Frequency Agile Magnetrons 527
19.10.3 Signal Injected Magnetrons 529
19.10.4 Beacon Magnetrons 532
19.10.5 Microwave Oven Magnetrons 532
19.10.6 Industrial Heating Magnetrons 534
19.10.7 Low-Noise Magnetrons 535
19.10.8 Relativistic Magnetrons 538
19.11 Summary of Power Capabilities 539
References 540
CHAPTER 20 CROSSED-FIELD AMPLIFIERS 543
20.1 Introduction 543
20.1.1 Injected-Beam CFAs 543
20.1.2 Distributed Emission CFAs 544
20.2 CFA Operation 547
20.2.1 Electron Emission and Hub Formation 547
20.2.2 Spoke Formation and Growth 549
20.3 CFA Slow Wave Circuits 552
20.4 CFA Performance 557
20.4.1 Forward Wave CFAs 558
20.4.2 Backward Wave CFAs 559
20.4.3 DC Operation 562
20.4.4 Gain and Operating Limits 563
20.4.5 CFA Phase Characteristics 567
20.4.6 Weight and Size Considerations 570
20.5 Power Capabilities 571
20.6 Thermal Considerations 572
20.7 CFA Power Supply Considerations 580
20.7.1 DC-Operated Supplies 580
20.7.2 Cathode Pulsing Supplies 580
References 581
CHAPTER 21 GYROTRONS 583
21.1 Introduction 583
21.2 Basic Interaction Mechanism 584
21.3 MIG Configuration and Requirements 590
21.3.1 MIG Configurations 590
21.3.2 First-Order Design Procedure 593
xii Klystrons, TWTs, Magnetrons, Crossed-Field Amplifiers, and Gyrotrons
21.3.3 MIG Performance 598
21.4 Beam-Wave Interaction 601
21.4.1 Hollow Cavities 601
21.4.2 Coaxial Cavities 604
21.4.3 Mode Converters 606
21.4.4 Harmonic Operation 609
21.4.5 Collectors 609
21.5 Gyro-Monotrons (Oscillators) 611
21.5.1 RF Output Coupling 611
21.5.2 Second-Harmonic Gyrotrons 613
21.5.3 Permanent Magnet Gyrotrons 613
21.6 Gyro-Amplifiers 615
21.6.1 Gyro-Klystrons 616
21.6.2 Gyro-Twystrons 617
21.6.3 Gyro-TWTs 617
21.7 Terahertz Gyrotrons 622
References 623
CHAPTER 22 WINDOWS 627
22.1 Background 627
22.2 Coaxial Windows 627
22.3 Waveguide Windows 629
22.4 Scaling of Windows 636
References 636
CHAPTER 23 NOISE 639
23.1 Thermal Agitation Noise 639
23.2 Definitions of Noise Figure 640
23.3 Overview of Noise Phenomena 641
23.4 Noise in Electron Guns 642
23.5 Noise Generation at the Cathode 644
23.5.1 Shot Noise 644
23.5.2 Velocity Noise 645
23.5.3 Other Noise Generation Mechanisms 645
23.6 The Space Charge Minimum Region 647
23.6.1 Rack Noise Invariance 647
23.6.2 Shot Noise Reduction 647
23.6.3 Other Noise Effects 649
23.7 Low-Velocity Correlation Region 650
23.8 High-Voltage Acceleration Region 653
23.8.1 Noise Space Charge Waves 653
23.8.2 Impedance Transformation for Low-Noise Tubes 655
Contents хш
23.8.3 Lens Effects 657
23.9 RF Section Noise Phenomena 659
23.9.1 Circuit Loss 659
23.9.2 Partition Noise 659
23.9.3 Secondary Electron Interactions 664
23.9.4 Noise Growth 661
23.9.5 Magnetic Noise Suppression 661
23.10 Other Noise Sources 663
23.11 Minimum Noise Figure of a TWT 664
References 664
CHAPTER 24 NONLINEARITIES AND DISTORTION 667
24.1 Distortion Resulting from Saturation Effects 667
24.1.1 AM/AM Conversion 667
24.1.2 AM/PM Conversion 669
24.1.3 Harmonic Generation 671
24.1.4 Intermodulation Products 673
24.2 Digital Communications 678
24.2.1 QPSK and 16QAM 680
24.2.2 Data Characteristics 682
24.2.3 Amplifier Design to Reduce Distortion 683
24.3 Signal Capturing 686
24.4 Variations with Frequency 687
24.4.1 Broadband Gain Variations 688
24.4.2 Narrowband Gain Variations 688
24.4.3 Phase Nonhnearities or Time Delay Distortion 689
24.5 Pushing and Pulling 690
24.5.1 Amplitude Pushing 691
24.5.2 Phase Pushing 694
24.5.3 Pulling 698
References 699
CHAPTER 25 BREAKDOWN AND PROTECTION 701
25.1 Field Enhancement 703
25.2 DC Breakdown in Vacuum 705
25.2.1 Electrode Phenomena Leading to Breakdown 706
25.2.2 Avoiding Breakdown 719
25.2.3 Vacuum Arcs 722
25.3 DC Breakdown on Insulator Surfaces 726
25.4 RF Breakdown in Vacuum 729
25.4.1 Two-Surface Multipactor with No Magnetic Field 730
25.4.2 Two-Surface Multipactor in Combined Fields 733