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Edited by Karl Jousten
Handbook of Vacuum Technology
Edited by Karl Jousten
Handbook of Vacuum Technology
Second, Completely Revised and Updated Edition
Editor
Dr. Karl Jousten
Physikalisch-Technische Bundesanstalt (PTB) AG Vakuummetrologie
Abbestr. 2 -12
10587 Berlin Germany
Cover Background by CERN
All books published by Wiley-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.
Library of Congress Card No.: applied for
British Library Cataloguing-in-Publication Data
A catalogue record for this book is available from the British Library.
Bibliographic information published by the Deutsche Nationalbibliothek
The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at http://dnb.d-nb.de
2016 Wiley-VCH Verlag GmbH & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany
All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, micro film, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.
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Printed on acid-free paper
Preface XXIII
1 The History of Vacuum Science and Vacuum Technology 1 References 16 Further Reading 17
2 Applications and Scope of Vacuum Technology 19 References 27
3 Gas Laws and Kinetic Theory of Gases 29
3.1 Description of the Gas State 29
3.1.1 State Variables 29
3.1.2 Extensive Quantities 33
3.1.3 Equation of State of an Ideal Gas 35
3.1.4 Mixtures of Different Gas Species 37
3.2 Kinetic Theory of Gases 38
3.2.1 Model Conceptions 38
3.2.2 Wall Pressure due to Impacting Particles 39
3.2.3 Maxwell–Boltzmann Velocity Distribution 41
3.2.4 Collision Rate and Effusion 44
3.2.5 Size of Gas Particles and Free Path 45
3.3 Transport Properties of Gases 50
3.3.1 Pressure Dependence 50
3.3.2 Transport of Frictional Forces in Gases and Viscosity 51
3.3.3 Transport of Heat in Gases and Thermal Conductivity 55
3.3.4 Diffusion 63
3.4 Real Gases 65
3.4.1 Equations of State 65
3.4.2 Particle Properties and Gas Behavior 69
3.5 Vapors 75
3.5.1 Saturation Vapor Pressure 75
3.5.2 Evaporation Rate 79
References 81
Comprehensive general treatments of the subject 82
4 Gas Flow 83
4.1 Types of Flows and Definitions 83
4.1.1 Characterizing Flow, Knudsen Number, and Reynolds Number 83
4.1.2 Gas Flow, Throughput, and Pumping Speed 87
4.1.3 Flow Resistance and Flow Conductance 90
4.1.4 Effective Pumping Speed of a Vacuum Pump 92
4.2 Inviscid Viscous Flow and Gas Dynamics 93
4.2.1 Conservation Laws 93
4.2.2 Gradual Change of Cross-Sectional Area: Isentropic Change of State 95
4.2.3 Critical Flow 98
4.2.4 Choked Flow at Low Outlet Pressure 100
4.2.5 Contraction of Flow into Aperture and Tube 101
4.2.6 Examples of Nozzle Flow 102
4.2.7 Straight and Oblique Compression Shocks 106
4.2.8 Laval Nozzle and Effluent Flow against Counterpressure 108
4.2.9 Flow Around a Corner (Prandtl–Meyer Flow) 111
4.3 Frictional–Viscous Flow through a Tube 114
4.3.1 Laminar and Turbulent Flows through a Tube 114
4.3.2 Airflow through a Tube 118
4.3.3 Air Inflow to a Vessel: Examples 120
4.3.4 Tube at the Inlet of a Pump: Examples 125
4.3.5 Flow through Ducts with Noncircular Cross Sections 128
4.3.6 Influence of Gas Species on Flow 130
4.4 Molecular Flow under High-Vacuum and Ultrahigh-Vacuum Conditions 131
4.4.1 Flow Pattern, Definitions, and Transmission Probability 131
4.4.2 Molecular Flow through an Aperture 135
4.4.3 Molecular Flow through a Tube with Constant Cross-Sectional Area 137
4.4.4 Molecular Flow through a Tube with Circular Cross Section 139
4.4.5 Molecular Flow through Tubes with Simple Cross-Sectional Geometry 140
4.4.6 Tube Bend and Tube Elbow 143
4.4.7 Series Connection of Tube and Aperture 145
4.4.8 Series Connection of Components 146
4.4.9 Molecular Flow through Conical Tube with Circular Cross Section (Funnel) 148
4.4.10 Component in the Inlet Line of a Pump 150
4.5 Flow throughout the Entire Pressure Range 151
4.5.1 Flow Ranges 151
4.5.2 Flow through a Thin Aperture with Circular Cross Section 151
4.5.3 Flow through a Long Tube with Circular Cross Section 154
4.6 Flow with Temperature Difference, Thermal Effusion, and Transpiration 158
4.7 Measuring Flow Conductances 162
4.7.1 Necessity of Measurement 162
4.7.2 Measurement of Intrinsic Conductances (Inherent Conductances) 162
4.7.3 Calculation of Reduced Conductance (Assembly Conductance) 164
4.7.4 Measuring Reduced Conductances 164 References 166 Further Reading 166
5 Analytical and Numerical Calculations of Rarefied Gas Flows 167
5.1 Main Concepts 167
5.1.1 Knudsen Number and Gas Rarefaction 167
5.1.2 Macroscopic Quantities 168
5.1.3 Velocity Distribution Function 168
5.1.4 Global Equilibrium 169
5.1.5 Local Equilibrium 170
5.1.6 Boltzmann Equation 170
5.1.7 Transport Coefficients 172
5.1.8 Model Equations 174
5.1.9 Gas–Surface Interaction 175
5.2 Methods of Calculations of Gas Flows 178
5.2.1 General Remarks 178
5.2.2 Deterministic Methods 178
5.2.3 Probabilistic Methods 179
5.3 Velocity Slip and Temperature Jump Phenomena 181
5.3.1 Viscous Slip Coefficient 182
5.3.2 Thermal Slip Coefficient 183
5.3.3 Temperature Jump Coefficient 184
5.4 Momentum and Heat Transfer Through Rarefied Gases 185
5.4.1 Planar Couette Flow 186
5.4.2 Cylindrical Couette Flow 189
5.4.3 Heat Transfer between Two Plates 193
5.4.4 Heat Transfer between Two Coaxial Cylinders 195
5.5 Flows Through Long Pipes 199
5.5.1 Definitions 199
5.5.2 Free Molecular Regime 201
5.5.3 Slip Flow Regime 202
5.5.4 Transitional Regime 203
5.5.5 Arbitrary Pressure and Temperature Drops 208
5.5.6 Variable Cross Section 214
5.5.7 Thermomolecular Pressure Ratio 216
5.6 Flow Through an Orifice 218
5.7 Modeling of Holweck Pump 221
5.8 Appendix A 223
5.8.1 Tables 223 References 225
6 Sorption and Diffusion 229
6.1 Sorption Phenomena and the Consequences, Definitions, and Terminology 229
6.2 Adsorption and Desorption Kinetics 234
6.2.1 Adsorption Rate 234
6.2.2 Desorption Rate 235
6.2.3 Hobson Model of a Pump-down Curve 238
6.2.4 Monolayer Adsorption Isotherms 242
6.2.5 Multilayer Adsorption and Brunauer–Emmett–Teller (BET) Isotherm 244
6.2.6 Monolayer Time 246
6.3 Absorption, Diffusion, and Outgassing 247
6.4 Permeation 254 References 256 Further Reading 256
7 Positive Displacement Pumps 259
7.1 Introduction and Overview 259
7.2 Oscillating Positive Displacement Pumps 262
7.2.1 Piston Pumps 262
7.2.2 Diaphragm Pumps 264
7.2.2.1 Design and Principle of Operation 264
7.2.2.2 Pumping Speed and Ultimate Pressure 265
7.2.2.3 Gas Ballast 266
7.2.2.4 Drive Concepts 267
7.2.2.5 Ultimate Pressure 267
7.2.2.6 Influence of Gas Species on Pumping Speed and Ultimate Pressure 269
7.2.2.7 Influence of Rotational Speed on Ultimate Pressure 269
7.2.2.8 Design Principles 269
7.2.2.9 Diaphragm Pumps in Chemical Laboratories 271
7.2.2.10 Diaphragm Pumps as Backing Pumps to Turbomolecular Pumps 272
7.2.2.11 Diaphragm Pumps Combined with Other Types of Vacuum Pumps 275
7.3 Single-Shaft Rotating Positive Displacement Pumps 276
7.3.1 Liquid Ring Vacuum Pumps 276
7.3.1.1 Design and Principle of Operation 277
7.3.1.2 Operating Properties and Dimensioning 278
7.3.1.3 Designs 281
7.3.1.4 Pump Units with Liquid Ring Vacuum Pumps 284
7.3.1.5 Suggestions for Economical Operation 286
7.3.2 Sliding Vane Rotary Pumps 287
7.3.2.1 Operating Principle and Design 288
7.3.2.2 Dry-Running Sliding Vane Rotary Pumps 289
7.3.2.3 Oil-Lubricated Sliding Vane Rotary Pumps 290
7.3.2.4 Once-Through Lubricated Sliding Vane Rotary Pumps 292
7.3.2.5 Operating Behavior and Recommendations 293
7.3.2.6 Characteristic Curves and Ratings 295
7.3.3 Rotary Plunger Pumps 296
7.3.3.1 Principle of Operation and Technical Design 296
7.3.3.2 A Comparison of Sliding Vane Rotary Pumps and Rotary Plunger Pumps 300
7.3.4 Trochoidal Pumps 300
7.3.5 Scroll Pumps 302
7.3.5.1 Principle of Compression 302
7.3.5.2 Design 303
7.3.5.3 Applications and Advantages 304
7.4 Twin-Spool Rotating Positive Displacement Pumps 305
7.4.1 Screw-Type Pumps 305
7.4.1.1 Operating Principle and Technical Design 305
7.4.1.2 Heat Behavior and Technical Notes 311
7.4.2 Claw Pumps 313
7.4.2.1 Compression Principle 314
7.4.2.2 Comparison with Roots Pumps 317
7.4.2.3 Multistage Claw Pumps and Pump Combinations 317
7.4.2.4 Speed Control 318
7.4.2.5 Fields of Application 319
7.4.3 Roots Pumps 319
7.4.3.1 Principle of Operation 319
7.4.3.2 Technical Setup 320
7.4.3.3 Theoretical Basics 322
7.4.3.4 Effective Gas Flow 322
7.4.3.5 Compression Ratio K0 at Zero Delivery 323
7.4.3.6 Effective Compression Ratio and Volumetric Efficiency 324
7.4.3.7 Gradation of Pumping Speed between Fore Pump and Roots Pump 325
7.4.3.8 Pumping Speed and Ultimate Pressure 329
7.4.3.9 Installation and Operating Suggestions 331
7.5 Specific Properties of Oil-Sealed Positive Displacement Pumps 331
7.5.1 Pumping Speed and Producible Ultimate Pressure 331
7.5.1.1 Pumping Speed and Ultimate Partial Pressure 332
7.5.1.2 Ultimate Pressure and Oil Selection 332
7.5.2 Oil Backflow 336
7.6 Basics of Positive Displacement Pumps 337
7.6.1 Pumping Down Vapors – Gas Ballast 337
7.6.2 Power Requirements 342
7.6.2.1 Isothermal Compression 343
7.6.2.2 Adiabatic Compression 343
Contents X
7.6.2.3 Polytropic Compression 343
7.6.2.4 Compression Power 344
7.7 Operating and Safety Recommendations 345
7.7.1 Installation 345
7.7.2 Starting and Shut Down, Inlet Valves 346
7.7.3 Pump Selection and Operating Recommendations 347
7.7.4 Technical Safety Recommendations 348
7.8 Specific Accessories for Positive Displacement Pumps 350
7.8.1 Sorption Traps 350
7.8.2 Safety Valves 351
7.8.3 Oil Filter and Oil Cleaning 352
7.8.4 Exhaust Filter (Oil–Mist Separator) 353
7.8.5 Dust Filters 355 References 356
Further Reading on Positive Displacement Pumps 359
8 Condensers 361
8.1 Condensation Processes Under Vacuum 361
8.1.1 Fundamentals 361
8.1.2 Condensation of Pure Vapors 363
8.1.3 Condensation of Gas–Vapor Mixtures 366
8.1.4 Coolants 369
8.2 Condenser Designs 370
8.2.1 Surface Condensers for Liquid Condensation 370
8.2.2 Direct Contact Condensers 372
8.2.3 Condensate Discharge 374
8.2.4 Surface Condensers for Solid Condensation 375
8.3 Integrating Condensers into Vacuum Systems 376
8.3.1 Condensers Combined with Vacuum Pumps 376
8.3.2 Control 379
8.4 Calculation Examples 380 References 382
9 Jet and Diffusion Pumps 383
9.1 Introduction and Overview 383
9.2 Liquid Jet Vacuum Pumps 385
9.3 Steam Jet Vacuum Pumps 387
9.3.1 Design and Function 387
9.3.2 Performance Data, Operating Behavior, and Control 389
9.3.3 Multistage Steam Jet Vacuum Pumps 393
9.3.4 Organic Vapors as Driving Pump Fluids 395
9.4 Diffusion Pumps 396
9.4.1 Design and Principle of Operation 396
9.4.2 Pump Fluids 400
9.4.3 Baffles and Vapor Traps 401
9.4.4 Fractionating and Degassing 403
9.4.5 Operating Suggestions 404
9.4.6 Pumping Speed, Critical Backing Pressure, Hybrid Pumps 405
9.4.7 Calculating Performance Characteristics of Diffusion and Vapor Jet Pumps by Using a Simple Pump Model 407
9.5 Diffusion Pumps Versus Vapor Jet Pumps 415 References 417
10 Molecular and Turbomolecular Pumps 419
10.1 Introduction 419
10.2 Molecular Pumps 421
10.2.1 Gaede Pump Stage 422
10.2.2 Holweck Pump Stage 426
10.2.3 Siegbahn Pump Stage 427
10.3 Molecular and Regenerative Drag Pump Combination 427
10.3.1 Regenerative Pump Mechanism 428
10.3.2 Pump Design and Applications 429
10.4 Physical Fundamentals of Turbomolecular Pump Stages 430
10.4.1 Pumping Mechanism 430
10.4.2 Pumping Speed and Compression Ratio 431
10.4.3 Gaede and Statistical Theory of the Pumping Effect 432
10.4.3.1 Consideration with Gaede 432
10.4.3.2 Statistical Consideration 434
10.4.4 Thermal Balance 436
10.5 Turbomolecular Pumps 439
10.5.1 Design and Function 439
10.5.2 Rotors of Turbomolecular Pumps 441
10.5.2.1 Rotor Design 441
10.5.2.2 Rotor Materials and Mechanical Requirements 442
10.5.3 Safety Requirements 442
10.5.4 Bearing Arrangements for Rotors in Turbomolecular Pumps 443
10.5.4.1 Shaft with Two Ball Bearings 444
10.5.4.2 Shaft With Permanent Magnet Bearing and Ball Bearing 445
10.5.4.3 Magnetic Bearings 445
10.5.5 Drives and Handling 447
10.5.6 Heating and Cooling 448
10.5.7 Special Designs 448
10.6 Performance Characteristics of Turbomolecular Pumps 450
10.6.1 Pumping Speed 450
10.6.2 Compression Ratio, Ultimate Pressure, and Base Pressure 451
10.6.3 Pump-down Times for Vacuum Chambers 452
10.6.4 Pumping of High Gas Throughputs 453
10.7 Operation and Maintenance of Turbomolecular Pumps 455
10.7.1 Backing Pump Selection 455
10.7.2 General Notes 455
10.7.3 Startup 455
10.7.4 Obtaining Base Pressure 456
10.7.5 Operation in Magnetic Fields 456
10.7.6 Venting 456
10.7.7 Maintenance 457
10.8 Applications 457
References 460
11 Sorption Pumps 463
11.1 Introduction 463
11.2 Adsorption Pumps 464
11.2.1 Working Principle 464
11.2.2 Design 466
11.2.3 Ultimate Vacuum and Pumping Speed 468
11.2.3.1 Ultimate Pressure with a Single Adsorption Pump 468
11.2.3.2 Ultimate Pressure with Two or More Adsorption Pumps 469
11.2.4 Operating Suggestions 471
11.3 Getter 472
11.3.1 Mode of Operation and Getter Types 472
11.3.2 NEG Pumps 474
11.3.2.1 Fundamentals of Bulk Getters/NEG 474
11.3.2.2 Design of NEG Pumps 478
11.3.2.3 Pumping Speed and Getter Capacity 479
11.3.2.4 Applications of NEG Pumps 481
11.3.2.5 Safety and Operating Recommendations 481
11.3.3 Evaporation/Sublimation Pumps 483
11.3.3.1 Evaporation Materials 483
11.3.3.2 Pumping Speed 484
11.3.3.3 Getter Capacity 486
11.3.3.4 Design of Evaporation Getters 487
11.4 Ion Getter Pumps 493
11.4.1 Working Principle 493
11.4.2 Technical Design (Diode Type) 497
11.4.3 Pumping Speed 498
11.4.4 The Differential Ion Pump 500
11.4.5 Triode Pumps 501
11.4.6 Distributed Ion Pumps 504
11.4.7 Residual Gas Spectrum 504
11.4.8 Operation 505
11.5 Orbitron Pumps 507
References 508
Further Reading 509
12 Cryotechnology and Cryopumps 511
12.1 Introduction 511
12.2 Methods of Refrigeration 512
12.2.1 Gas Refrigeration Processes 513
12.2.1.1 Stirling Process 515
12.2.1.2 Gifford–McMahon Process 516
12.2.1.3 Pulse Tube Process 518
12.2.2 Cryostat with Liquid Cryogens 519
12.2.3 Measurement of Low Temperatures 520
12.3 Working Principles of Cryopumps 520
12.3.1 Gas Condensation 523
12.3.2 Cryosorption 525
12.3.2.1 Solid Adsorbents 526
12.3.2.2 Cryotrapping 530
12.4 Design of Cryopumps 531
12.4.1 Cryotechnological Constructive Parameters 531
12.4.1.1 Thermal Radiation 531
12.4.1.2 Thermal Conduction 535
12.4.2 Vacuum Technology: Design Parameters 538
12.4.3 Construction Principles 541
12.4.3.1 Bath Cryopumps 541
12.4.3.2 Refrigerator Cryopumps 543
12.5 Characteristics of a Cryopump 547
12.5.1 Starting Pressure 547
12.5.2 Ultimate Pressure 548
12.5.3 Pumping Speed 549
12.5.4 Service Life 550
12.5.5 Capacity (Maximum Gas Intake) 552
12.5.6 Crossover Value 552
12.5.7 Maximum Tolerable pV Flow 552
12.5.8 Resistance to Thermal Radiation 552
12.5.9 Regeneration 552
12.5.10 Performance Comparison 555
12.6 Application Examples 555
12.6.1 Cryopumps with Forced Cooling Using Supercritical Helium 556
12.6.2 Combined Refrigerator/Liquid Cryopumps 558
12.6.3 Cryopumps with Forced Cooling Using Liquid Cryogen 559
12.6.4 Cryopumps in Large Research Applications 560
12.6.5 Cryopumps in Industrial Facilities 561
12.6.6 Development Trends for Cryopumps 561
References 562
13 Total Pressure Vacuum Gauges 565
13.1 Introduction 565
13.2 Mechanical Vacuum Gauges 566
13.2.1 Principle and Classification 566
13.2.2 Corrugated-Diaphragm Vacuum Gauges 567
13.2.3 Capsule Element Vacuum Gauges (Measuring Range 1–100 kPa) 568
13.2.4 Bourdon Tube Vacuum Gauges (Measuring Range 1–100 kPa) 569
13.2.4.1 Quartz Bourdon Tube Vacuum Gauges 570
13.2.5 Diaphragm (Membrane) Vacuum Gauges 571
13.2.5.1 Diaphragm (Membrane) Vacuum Gauges with Mechanical Displays (Measuring Range 0.1–100 kPa) 571
13.2.5.2 Diaphragm (Membrane) Vacuum Gauges with Electrical Converters 572
13.2.5.3 Diaphragm (Membrane) Vacuum Gauges Using the Piezoresistive Principle 574
13.2.5.4 Piezoelectric Vacuum Gauges 575
13.2.5.5 Resonant Diaphragm Vacuum Gauges 575
13.2.5.6 Capacitance Diaphragm Vacuum Gauges 576
13.2.5.7 Thermal Transpiration 580
13.2.6 Pressure Switches and Pressure Controllers 582
13.3 Spinning Rotor Gauges (Gas-Friction Vacuum Gauges) 584
13.3.1 Measuring Setup and Measuring Principle 584
13.3.2 Retarding Effect due to Gas Friction 586
13.3.3 Measuring Procedure 590
13.3.4 Extending the Measuring Range toward Higher Pressures 592
13.3.5 Measuring Uncertainty 592
13.4 Direct Electric Pressure Measuring Transducers 593
13.5 Thermal Conductivity Vacuum Gauges 594
13.5.1 Principle 594
13.5.2 Thermal Conductivity Vacuum Gauges with Constant Wire Temperature 597
13.5.3 Thermal Conductivity Vacuum Gauges with Constant Heating 601
13.5.4 Thermocouple Vacuum Gauges 602
13.5.5 Thermistors 603
13.5.6 Guidelines for Operating Thermal Conductivity Vacuum Gauges 603
13.6 Thermal Mass Flowmeters 604
13.7 Ionization Gauges 607
13.7.1 Principle and Classification 607
13.7.2 History of Ionization Gauges 608
13.7.3 Emitting-Cathode Ionization Gauges (Hot-Cathode Ionization Gauges) 610
13.7.3.1 Measurement Principle 610
13.7.3.2 Design of Emitting-Cathode Ionization Gauges (Hot-Cathode Ionization Gauges) 613
13.7.3.3 Concentric Triode 614
13.7.3.4 Fine-Vacuum Ionization Gauges 614
13.7.3.5 Bayard–Alpert Ionization Gauges 615
13.7.3.6 Extractor Ionization Gauges 620
13.7.3.7 Additional Types of Emitting-Cathode Ionization Gauges 623
13.7.3.8 Operating Suggestions for Emitting-Cathode Ionization Gauges 623
13.7.4 Crossed-Field Ionization Gauges 625
13.7.4.1 Penning Gauges 625
13.7.4.2 Magnetron and Inverted Magnetron 630
13.7.5 Comparison of Both Types of Ionization Gauges 631
13.7.6 General Suggestions 633
13.8 Combined Vacuum Gauges 637
References 639
14 Partial Pressure Vacuum Gauges and Leak Detectors 643
14.1 Introduction 643
14.2 Partial Pressure Analysis by Mass Spectrometry 643
14.2.1 Ion Source Design 648
14.2.1.1 Open Ion Sources (OIS) 649
14.2.1.2 Closed Ion Sources (CIS) 651
14.2.1.3 Molecular Beam Ion Sources (MBIS) 652
14.2.2 Filament Materials 652
14.2.3 Artifacts in the Mass Spectrum due to the Ion Source 654
14.2.4 Mass Analyzers 655
14.2.4.1 Quadrupole Mass Analyzers 655
14.2.4.2 Miniaturized Quadrupole Mass Analyzers 659
14.2.4.3 Magnetic Sector Analyzers 661
14.2.4.4 Autoresonant Ion Trap Mass Analyzers 664
14.2.5 Ion Detectors 665
14.2.5.1 Faraday Cups 665
14.2.5.2 SEM Detection 666
14.2.5.3 Discrete Dynode Electron Multipliers 667
14.2.5.4 Continuous Dynode Electron Multipliers (CDEM) 668
14.2.5.5 Microchannel Plate Detectors 669
14.2.6 Software for Mass Spectrometer Control 670
14.2.6.1 Analog Scan, Ion Current versus Mass 670
14.2.6.2 Selected Peaks, Ion Current versus Time 671
14.2.6.3 Leak Detection Mode 671
14.2.7 Further Applications of Mass Spectrometers 671
14.3 Partial Pressure Measurement Using Optical Methods 672
14.4 Leak Detectors 675
14.4.1 Basic Principles and Historical Overview 675
14.4.2 Helium Leak Detectors 675
14.4.2.1 Requirements and General Functions of Vacuum Leak Detection 675
14.4.2.2 Helium Sector Field Mass Spectrometers 676
14.4.2.3 Inlet Pressure of Helium Leak Detectors 677
14.4.2.4 Time Response of Helium Leak Detectors 678
14.4.2.5 Operating Principles of Helium Leak Detectors 679
14.4.2.6 Sniffing Devices for Helium Leak Detectors 683
14.4.2.7 Applications of Mass Spectrometer Helium Leak Detectors 684
14.4.3 Refrigerant Leak Detectors 685
14.4.3.1 Design and Operating Principle 685
14.4.3.2 Applications 687
14.4.4 Reference Leaks 687
14.4.4.1 Permeation Leaks 687
14.4.4.2 Conductance Leaks 688
14.4.4.3 Practical Realization of Reference Leaks 688
14.4.4.4 Calibrating Reference Leaks 689
14.4.5 Measuring Characteristics and Calibration of Leak Detectors 689
14.4.5.1 Leak Detectors as Test Equipment According to ISO 9001 689
14.4.5.2 Calibration Uncertainty 690
14.4.6 Leak Detectors Based on Other Sensor Principles 691
14.4.6.1 Helium Sniffers with Quartz Glass Membrane 691
14.4.6.2 Halogen Leak Detectors with Alkali Ion Sensors 691
14.4.6.3 Halogen Leak Detectors with Infrared Sensors 692 References 692
15 Calibrations and Standards 697
15.1 Introduction 697
15.2 Calibration of Vacuum Gauges 700
15.2.1 Primary Standards 700
15.2.1.1 Liquid Manometers 701
15.2.1.2 Compression Manometer after McLeod 704
15.2.1.3 Piston Gauges and Pressure Balances 707
15.2.1.4 Static Expansion Method 710
15.2.1.5 Continuous Expansion Method 716
15.2.1.6 Other Primary Standards 722
15.2.2 Calibration by Comparison 723
15.2.3 Capacitance Diaphragm Gauges 724
15.2.4 Spinning Rotor Gauges 728
15.2.5 Ionization Gauges 731
15.3 Calibrations of Residual Gas Analyzers 733
15.4 Calibration of Test Leaks 735
15.5 Standards for Determining Characteristics of Vacuum Pumps 738 References 742
16 Materials 747
16.1 Requirements and Overview of Materials 747
16.2 Materials for Vacuum Technology 749
16.2.1 Metals 749
16.2.1.1 The Most Important Metals and Metal Alloys 749
16.2.2 Technical Glass 753
16.2.2.1 Basics 753
16.2.2.2 Properties of Important Glasses 755
16.2.3 Ceramic Materials 757
16.2.3.1 Basics 757
16.2.3.2 Properties of Important Ceramics 757
16.2.3.3 Ceramics in Vacuum Technology 758
16.2.3.4 Ceramic/Metal Joining Technologies 758
16.2.3.5 Zeolite 758
16.2.4 Plastics 760
16.2.4.1 Basics 760
16.2.4.2 Properties of Major Plastics 760
16.2.5 Vacuum Greases 760
16.2.6 Oils 762
16.2.7 Coolants 763
16.3 Gas Permeability and Gas Emissions of Materials 763
16.3.1 Fundamentals 763
16.3.2 Gas Permeability 763
16.3.2.1 Gas Permeability of Metals 764
16.3.2.2 Gas Permeability of Glasses and Ceramics 764
16.3.2.3 Gas Permeability of Plastics 767
16.3.3 Gas Emissions 768
16.3.3.1 Basics 768
16.3.3.2 Saturation Vapor Pressure 768
16.3.3.3 Surface Desorption, Gas Diffusion from Bulk Material, Reference Values for Gas Emissions 770
16.3.4 Gas Diffusion from Bulk Material 770
16.3.5 Reference Values for Total Gas Emission Rates 774 References 774 Further Reading 775
17 Vacuum Components, Seals, and Joints 777
17.1 Introduction 777
17.2 Vacuum Hygiene 778
17.3 Joining Technologies in Vacuum Technology 781
17.3.1 Permanent Connections 783
17.3.1.1 Welding 784
17.3.1.2 Brazing 786
17.3.1.3 Adhesive Bonding 791
17.3.2 Detachable Connections 793
17.3.2.1 Elastomer-Sealed, Static, Detachable Connections (KF, ISO, and Others) 794
17.3.2.2 Metal-Sealed, Static, Detachable Connections 802
17.4 Components 806
17.4.1 Standard Components and Chambers 806
17.4.2 Mechanical Feedthroughs 813
XVIII Contents
17.4.3 Valves 817
17.4.4 Electrical Feedthroughs 823
17.4.5 Optical Feedthroughs 829
17.4.6 Heat Supply and Dissipation 833 Abbreviations 839 References 840
18 Operating Vacuum Systems 843
18.1 Electronic Integration of Vacuum Systems 843
18.1.1 Control by Means of Process Sensors and Automated Data Processing 843
18.1.1.1 Requirements and Applications 843
18.1.2 Integrated Solutions 845
18.1.2.1 ASCII Protocols 846
18.1.2.2 Standardized Bus Systems 846
18.1.2.3 Sensor Integration According to SECS and HSMS Standards 847
18.1.2.4 Process-Data Analysis 849
18.2 Calculation of Vacuum Systems 851
18.2.1 Analytical and Numerical Calculation 851
18.2.2 Calculation by Analog Electrical Network 852
18.2.3 Ultimate and Working Pressure in Vacuum Systems 854
18.2.3.1 Ultimate Pressure 854
18.2.3.2 Operating Pressure 855
18.3 Pressure Control 859
18.4 Techniques for Operating Low-Vacuum Systems 860
18.4.1 Overview 860
18.4.2 Assembly of Low-Vacuum Systems 861
18.4.3 Pumps: Types and Pumping Speeds 862
18.4.4 Low-Vacuum Pump Stands 862
18.4.5 Low-Vacuum Pressure Measurement 864
18.4.6 Pressure and Pump-Down Times in Low Vacuum 864
18.4.7 Venting 869
18.5 Techniques for Operating Fine-Vacuum Systems 870
18.5.1 Overview 870
18.5.2 Assembly of Fine-Vacuum Systems 870
18.5.3 Pumps: Types and Pumping Speeds 871
18.5.4 Pressure Measurement 871
18.5.5 Pump-Down Time and Ultimate Pressure 872
18.5.6 Venting 877
18.5.7 Fine-vacuum Pump Stands 877
18.6 Techniques for Operating High-Vacuum Systems 879
18.6.1 Pumps: Types and Pumping Speeds 879
18.6.2 Cleaning of Vacuum Gauges 880
18.6.3 High-Vacuum Pump Stands 882
18.6.3.1 High-Vacuum Pump Stands with Diffusion Pumps 882
18.6.3.2 High-Vacuum Pump Stands with Turbomolecular Pumps 889
18.6.3.3 Fully Automatic High-Vacuum Pump Stands 890
18.6.4 Pump-Down Time and Venting 891
18.7 Techniques for Operating Ultrahigh-Vacuum Systems 892
18.7.1 Overview 892
18.7.2 Operating Guidelines for UHV Pumps 893
18.7.2.1 Adsorption Pumps 894
18.7.2.2 Ion Getter Pumps 894
18.7.2.3 Titanium Evaporation Pumps 895
18.7.2.4 Turbomolecular Pumps 896
18.7.2.5 Cryopumps 896
18.7.2.6 Bulk Getter (NEG) Pumps 896
18.7.3 Pressure Measurement 897
18.7.4 Pump-Down Times, Ultimate Pressure, and Evacuating Procedures 897
18.7.5 Venting 898
18.7.6 Ultrahigh-Vacuum Systems 898
18.7.7 Ultrahigh-Vacuum (UHV) Components 898
18.7.8 Ultrahigh-Vacuum (UHV) Pump Stands 899
18.7.8.1 Large Ultrahigh-Vacuum (UHV) Facilities 901 References 904
19 Methods of Leak Detection 907
19.1 Overview 907
19.1.1 Vacuum Leak Detection 907
19.1.2 Overpressure Leak Detection 908
19.1.3 Tracer-Gas Distribution in the Atmosphere in Front of a Leak 909
19.1.4 Measurement Results with the Sniffing Method 910
19.1.5 Tracer-Gas Species 911
19.1.5.1 Helium 911
19.1.5.2 Noble Gases Other Than Helium 911
19.1.5.3 Hydrogen H2 911
19.1.5.4 Methane CH4 912
19.1.5.5 Carbon Dioxide CO2 912
19.1.5.6 Sulfur Hexafluoride SF6 912
19.2 Properties of Leaks 912
19.2.1 Leak Rate, Units 912
19.2.2 Types of Leaks 913
19.2.2.1 Properties of Pore-like Leaks 914
19.2.2.2 Permeation Leaks 916
19.2.2.3 Virtual Leaks in Vacuum Vessels 917
19.2.2.4 Liquid Leaks 917
19.3 Overview of Leak-Detection Methods (See Also DIN EN 1779) 918
19.3.1 General Guidelines for Tightness Testing 918
19.3.2 Methods without Tracer Gas (Pressure Testing) 919
19.3.2.1 Introduction 919
19.3.2.2 Pressure Loss Measurement 920
19.3.2.3 Pressure Rise Measurement 920
19.3.2.4 Additional Methods 922
19.3.3 Tracer-Gas Methods without Helium 922
19.3.3.1 Basics 922
19.3.3.2 Vacuum Leak Detection with Non-helium Tracer Gas 923
19.3.3.3 Overpressure Leak Detection with Tracer Gases Other Than Helium 924
19.4 Leak Detection Using Helium Leak Detectors 925
19.4.1 Properties of Helium Leak Detectors 925
19.4.2 Testing of Components 926
19.4.2.1 Testing Procedure, Integral Testing 926
19.4.2.2 Procedure for Leak Localization 927
19.4.3 Testing of Vacuum Systems 929
19.4.3.1 General Considerations for Partial Flow Operation 930
19.4.3.2 Points on Systems for Connecting Leak Detectors 931
19.4.3.3 Detection Limit and Response Time 933
19.4.4 Overpressure (Sniffing) Leak Detection with a Helium Leak Detector 934
19.4.4.1 Integral Procedure (Total or Partial) 935
19.4.4.2 Leak Localization with a Sniffer 936
19.5 Leak Detection with Other Tracer Gases 936
19.5.1 Basics 936
19.5.2 Sniffing Leak Detection on Refrigerators and Air Conditioners 936
19.6 Industrial Tightness Testing of Mass-Production Components 937
19.6.1 Basics 937
19.6.2 Industrial Testing of Series Components 937
19.6.2.1 Envelope Testing Method for Vacuum Components (Method A1 in EN 1779) 938
19.6.2.2 Vacuum Chamber Method for Overpressure Components (Method B6 in EN 1779) 938
19.6.2.3
Testing of Hermetically Sealed Components by Means of Bombing (Method B5 in EN 1779) 940
19.6.2.4 Testing of Food Packaging in Flexible Test Chambers 941 References 942 Further Reading 942
Appendix 943
Index 1003
Directory of Products and Suppliers 1023
Preface
In 2008, Wiley-VCH published a translation of the ninth edition of the German handbook “Wutz – Handbook of Vacuum Technology,” named after the author of the first edition Max Wutz. This book has been a great success for five decades and the object of many requests for a translation. Since its second edition, the “ Wutz – Handbook of Vacuum Technology” has become a multi-author book covering the fi eld of vacuum science, vacuum technology, and vacuum techniques comprehensively. Since 2008, the German handbook underwent significant changes and when it could be foreseen that the English edition would run out of print, Wiley-VCH suggested to issue a second English edition “Handbook of Vacuum Technology,” which is a translation of the 11th German edition of the “ Wutz – Handbook of Vacuum Technology,” published by Springer Vieweg. Chapter 17, however, received a new author and was newly written for this second English edition. Compared with the first English edition, also Chapters 10 and 12 were written by new authors while improvements were made in most of the other chapters according to the changes in techniques.
Although multi-author, the book aims to be read as a single-author work, a goal to which the present editor who himself has revised almost half of the content has stringently adhered to. The style is as uniform as possible, there are only recurrences where necessary, and the same symbols and notation are used throughout. Hence, the book has taken on textbook character, though it was originally intended to be used as a technical handbook.
The main idea of the book is to cover all aspects of vacuum science and technology in order to enable engineers, technicians, and scientists to develop and work successfully with the equipment and “environment” of vacuum. Beginners in the field of vacuum shall be able to start and experts shall be able to deepen their knowledge and find the necessary information and data to continue their work.
Despite the fact that the applications of vacuum technology are steadily increasing both quantitatively and qualitatively – note, for instance, that the next chip generation will be illuminated under vacuum by extreme ultraviolet (EUV) lithography – the number of scientists researching and teaching in the field is on a steady decline. Thus, another task for a book like this is to both preserve the knowledge of vacuum science and technology and enable self-studying
XXIV Preface
in the field. For this reason, the book may be at times too introductive and simple for experts and sometimes too specialized for beginners. The reader should not be discouraged when experiencing this, but rather choose the information as his/her personal level requires. Short explanations following the title of each chapter describe the contents and may help the reader to choose the right chapter for his/her needs.
We hope that also this second edition will be helpful to all readers of English interested in a comprehensive and up-to-date overview in the field of vacuum technology including its underlying science.
Even after many people read drafts and proofs, there will always be mistakes in a book of this size. If you discover such or if you have any suggestions for improvements, please send an email to the editor (karl.jousten@ptb.de). I will be glad to consider your suggestions in future editions.
June 2015 Karl Jousten Berlin, Germany
The History of Vacuum Science and Vacuum Technology
Dr. Karl Jousten
Physikalisch-Technische Bundesanstalt, Vacuum Metrology, Abbestr. 2-12, 10587, Berlin, Germany
In old Greece, before the time of Socrates, the philosophers searched for the constancy in the world, that is, what is behind the daily experience. The Greek philosopher Democritus (circa 460 to 375 BC) (Figure 1.1) assumed that the world was made up of many small and undividable particles that he called atoms (atomos, Greek: undividable). In between the atoms, Democritus presumed empty space (a kind of microvacuum) through which the atoms moved according to the general laws of mechanics. Variations in shape, orientation, and arrangement of the atoms would cause variations of macroscopic objects.
Acknowledging this philosophy, Democritus, together with his teacher Leucippus, may be considered as the inventor of the concept of vacuum. For them, the empty space was the precondition for the variety of our world, since it allowed the atoms to move about and arrange themselves freely. Our modern view of physics corresponds very closely to this idea of Democritus. However, his philosophy did not dominate the way of thinking until the sixteenth century.
It was Aristotle’ s (384 to 322 BC) philosophy that prevailed throughout the Middle Ages and until the beginning of modern times. In his book Physica [1], around 330 BC, Aristotle denied the existence of an empty space. Where there is nothing, space could not be defined. For this reason, no vacuum (Latin: empty space, emptiness) could exist in nature. According to his philosophy, nature consisted of water, earth, air, and fi re. The lightest of these four elements, fire, is directed upward, whereas the heaviest, earth, downward. Additionally, nature would forbid vacuum since neither up nor down could be de fi ned within it. Around 1300, the medieval scholastics began to speak of a horror vacui, meaning nature’ s fear of vacuum. Nature would abhor vacuum and wherever such a vacuum may be on the verge to develop, nature would fill it immediately.
Around 1600, however, the possibility or impossibility of an evacuated volume without any matter was a much-debated issue within the scientific–philosophical community of Italy, and later in France and Germany as well. This happened at the time when the first scientists were burnt at the stake (Bruno in 1600).
Handbook of Vacuum Technology, Second Edition. Edited by Karl Jousten. 2016 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2016 by Wiley-VCH Verlag GmbH & Co. KGaA.
In 1613, Galileo Galilei in Florence attempted to measure the weight and density of air. He determined the weight of a glass flask containing either compressed air, air at atmospheric pressure, or water. He found a value of 2 2g ℓ 1 for the density of air (the modern value is 1:2g ℓ 1 ). This was a big step forward: air could now be considered as a substance with weight. Therefore, it could be assumed that air, in some way, could also be removed from a volume.
In 1630, Galilei was in correspondence with the Genoese scientist Baliani discussing the water supply system of Genoa. Galilei argued that, for a long time, he had been aware of the fact that the maximum height of a water column in a vertical pipe produced by a suction pump device was about 34 feet. Baliani replied that he thought this was due to the limited pressure of the atmosphere!
One can see from these examples that in Italy in the fi rst half of the seventeenth century the ground was prepared for an experiment, which was performed in 1640 by Gasparo Berti and in 1644 by Evangelista Torricelli,a professor in Florence. The Torricelli experiment was bound to be one of the key experiments of natural sciences.
Torricelli filled a glass tube of about 1 m in length with mercury. The open end was sealed with a fingertip. The tube was then brought to an upright position with the end pointing downward sealed by the fingertip. This end was immersed in a mercury reservoir and the fingertip removed so that the mercury inside the tube was in free contact with the reservoir. The mercury column in the tube sank to a height of 76 cm, measured from the liquid surface of the reservoir.
Figure 1.2 shows a drawing of the Torricellian apparatus.
The experiment demonstrated that the space left above the mercury after turning the tube upside down was in fact a vacuum: the mercury level was independent of the volume above, and it could be fi lled completely with water
1.2
’s vacuum experiment in 1644. The level AB of mercury in both tubes C and D was equal, independent of the size of the additional volume E in tube D. (From Ref. [2].)
admitted from below. This experiment was the first successful attempt to produce vacuum and subsequently convinced the scientific community. An earlier attempt by Berti who used water was less successful.
In 1646, the mathematician Pierre Petit in France informed Blaise Pascal (Figure 1.3) about Torricelli’ s experiment. Pascal repeated the experiment and, in addition, tried other types of liquid. He found that the maximum height was exactly inversely proportional to the used liquid’ s density. Pascal knew the equally famous philosopher Descartes. During a discussion in 1647, they developed the idea of air pressure measurements at different altitudes using a Torricellian tube.
Pascal wrote a letter to his brother-in-law Périer and asked him to carry out the experiment on the very steep mountain Puy de Dôme, close to Périer’ s home.
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number of cases; the only authority of weight who opposes this view is Charcot, and his opposition is abundantly neutralized by a number of carefully-studied American and European cases.
145 The coincidences among these three cases were remarkable. All three were Germans, all three musicians, two had lost an only son. In all, the emotional manifestations were pronounced from the initial to the advanced period of the disease.
146 A Bohemian cigar-maker was startled by the sudden firing of a pistol-shot in a dark hallway, and on arriving at the factory, and not fully recovered from the first fright, he was again startled by the sudden descent of an elevator and the fall of a heavy case from it close to where he stood. From the latter moment he trembled, and his tremor continued increasing till the last stage of his illness was reached. This was my shortest duration, four years, and of nuclear oblongata paralysis type.
Hysterical and other obscure neuroses have been claimed to act as predisposing causes. But, inasmuch as it is well established that sclerosis is not a legitimate sequel of even the most aggravated forms of true hysteria,147 and, on the other hand, that disseminated sclerosis, particularly in the early stages, may progress under the mask of spinal irritative or other neuroses, it is reasonable to suppose that cause and effect have been confounded by those who advanced this view. According to Charcot, the female sex shows a greater disposition to the disease than the male. Erb, who bases his remarks on the surprisingly small number of nine cases, is inclined to account for Charcot's statement on the ground that it was at a hospital for females that Charcot made his observations. On comparing the figures of numerous observers, it will be found that in the experience of one the females, and of the other the males, preponderate. In my own experience the males far exceed the females both in private and in dispensary practice. Of 22 cases with accessible records, only 7 were females.
147 Charcot's observation of lateral sclerosis in hysterical contracture, although made so long ago, has not been confirmed, and the most careful examinations in equally severe and protracted cases have proven altogether negative.
Syphilis has also been assigned as a cause. The connection is not as clear as in tabes. In the few cases where there appears to be a direct causal relation the lesion is not typical. There are sclerotic foci, but in addition there is a general lesion, particularly of the posterior columns of the cord, such as is found with paretic dementia. And it has been noted that periendymal and subendymal sclerosis is more frequent with the cases of alleged syphilitic origin than with those of the typical form.
DIFFERENTIAL DIAGNOSIS
.—In view of what has been already stated regarding the numerous clinical types found in disseminated sclerosis, it is easily understood why the diagnosis of this disease is becoming more and more uncertain: every new set of researches removes some one or several of the old and cherished landmarks; and it may be safely asserted that only a minority of the cases show that symptom-group which was formerly claimed as characteristic of all. The discovery of a series of cases by Westphal,148 in which the typical symptom-group of Charcot was present, but no sclerosis deserving the name found after death, as well as the interesting experience of Seguin, who found well-marked disseminated sclerosis in a case regarded as hysterical intra vitam, illustrates the increasing uncertainly of our advancing knowledge. It was believed within a few years that the presence of cranial nerve-symptoms was a positive factor in determining a given case to be one of disseminated sclerosis, but in the very cases described by Westphal such symptoms were present notwithstanding the lesion was absent. Up to this time, however, no case has been discovered in which, optic-nerve atrophy being present in addition to the so-called characteristic symptoms of intention tremor, nystagmus, and scanning in speech, disseminated foci of sclerosis were not found at the autopsy. This sign may be therefore regarded as of the highest determining value when present; but as it is absent in the majority of cases, its absence cannot be regarded as decisive. The presence of pupillary symptoms also increases the certainty of the diagnosis when added to the ordinary and general symptoms of the disorder related above.
148 Archiv für Psychiatrie, xiv. p. 128.
Although the difference between the tremor of typical disseminated sclerosis and that of paralysis agitans is pathognomonic, yet the existence of a group of cases of disseminated sclerosis, as well as of one of cases of paralysis agitans without tremor, renders an exact discrimination in all cases impossible. It is a question, as yet, whether the form of paralysis agitans without tremor described by Charcot, and which is marked by pains in the extremities, rigidity, clumsiness, and slowness of movement, general motor weakness, a frozen countenance, impeded speech, and mental enfeeblement, is not in reality a diffuse or disseminated sclerosis.
The diagnosis of this disease, while readily made in a large number of cases on the strength of the characteristic symptoms detailed, may be regarded as impossible in a minority which some good authorities incline to regard as a large one.
Diffuse Sclerosis.
SYNONYMS.—Chronic myelitis, Diffuse myelitis, Simple or Diffuse spinal sclerosis, Chronic transverse myelitis, Sclerosis stricte sic dicta (Leyden, in part), Gray degeneration.
The various forms of sclerosis thus far considered were at one time considered as varieties of chronic myelitis, and under different names, founded on leading symptoms, were considered to be merely local, and perhaps accidental, variations of one and the same morbid process. More accurate clinical and pathological analysis has separated from the general family of the scleroses one clearly demarcated form after another. Tabes dorsalis, disseminated sclerosis, amyotrophic lateral sclerosis, and the combined forms of sclerosis have been successively isolated. Still, a large number of cases are left which cannot be classified either with the regular affections of the cord, limited to special systems of fibres, or with the
disseminated form last considered. They agree with the latter in that they are not uniform; they differ from it in that they are not multilocular. Not a few modern authors have neglected making any provisions for these cases, while others treat of them in conjunction with acute myelitis, of which disease it is sometimes regarded as a sequel. The term diffuse sclerosis is here applied to those forms of chronic myelitis which follow no special rule in their location, and to such as are atypical and do not correspond in their symptomatology or anatomy to the more regular forms of sclerosis. In regional distribution the foci of diffuse sclerosis imitate those of acute myelitis: they may be transverse, fascicular, or irregular.
MORBID ANATOMY.—In typical cases the lesion of diffuse sclerosis constitutes a connecting-link between that of the disseminated form and posterior sclerosis. Its naked-eye characters are the same. There is usually more rapid destruction of the axis-cylinders, more inflammatory vascularization, proliferation of the neuroglia-nuclei, and pigmentary and hyaline degeneration of the nerve-cells, than in the disseminated form.
Syphilitic inflammation of the cord extends along the lymphatic channels, including the adventitial spaces, and leads to a diffuse fibrous interstitial sclerosis. In one case in which I suspected syphilis, though a fellow-observer failed to detect it after a rigid search, I found a peculiar form of what would probably be best designated as vesicular degeneration, according to Leyden, though associated with a veritable sclerosis. The lymph-space in the posterior septum showed ectasis; the blood-vessels were sclerotic, and each was the centre of the mingled sclerotic and rarefying change. It appears that while the interstitial tissue hypertrophied, the myelin of adjoining nerve-tubes was pressed together till the intervening tissue underwent pressure atrophy. The result was, the myelin-tubes consolidated, some axis-cylinders perished, others atrophied, a few remained, and, the myelin undergoing liquefaction, long tubular cavities resulted, running parallel with the axis of the cord, and exposed as round cavities on cross-section (Fig. 32). The changes in the cells of the anterior horn in the same cord (Fig. 33) illustrate one
of the common forms of disease to which they are subjected in the course of sclerotic disease.
The so-called myelitis without softening, or hyperplastic myelitis of Dujardin-Beaumetz, which is ranked by Leyden and Erb among the acute processes, properly belongs here. It is characterized by a proliferation of the interstitial substance, both of its cellular and fibrillar elements. The nerve-elements proper play no part, or at best a very slight or secondary one. In the sense that this affection occurs after acute diseases and develops in a brief period it may be called an acute myelitis, but both in its histological products and its clinical features it approximates the sclerotic or chronic inflammatory affections of the cord. As far as the clinical features are concerned, this is particularly well shown in the disseminated myelitis found by Westphal after acute diseases, such as the exanthematous and continued fevers.
CLINICAL HISTORY.—Impairment of motion is the most constant early feature of chronic myelitis; in the transverse form it may be as absolute as in the severest forms of acute myelitis; as a rule, however, it is rather a paresis than a paralysis. The patient is usually able to walk, manifesting the paraparetic gait: he moves along
slowly, does not lift his feet, drags them along, makes short steps; in short, acts as if his limbs were heavily weighted. This difficulty of locomotion is preceded and accompanied by a tired feeling before other sensory symptoms are developed. Rigidity of the muscles, like that found in disseminated sclerosis, is a common accompaniment, and may even preponderate over the paresis to such an extent as to modify the patient's walk, rendering it spastic in character. In such cases the muscles feel hard to the touch, and the same exaggerated reflex excitability may be present as was described to be characteristic of spastic paralysis.
If, while the leg is slightly flexed on the thigh, the foot be extended,149 so as to render the Achilles tendon and the muscles connected with it tense, and the hand while grasping the foot suddenly presses the latter to still further extension, a quick contraction occurs, which, if the pressure be renewed and kept up, recurs again and again, the succession of the involuntary movements resembling a clonic spasm. This action is termed the ankle-clonus or foot-phenomenon. Gowers has amplified this test of exaggerated reflex excitability by adding what he calls the front-tap contraction. The foot being held in the same way as stated above, the examiner strikes the muscles on the front of the leg; the calf-muscles contract and cause a brief extension movement of the foot. It is believed that the foot-clonus and the front-tap contraction are always pathological, but a few observers, notably Gnauck, leave it an open question whether it may not occur in neurotic subjects who have no organic disease. Gowers considers the foot-clonus found in hysterical women as spurious, and states that it differs from the true form in that it is not constant, being broken by voluntary contractions, and does not begin as soon as the observer applies pressure. But I have seen the form of clonus which Gowers regards as hysterical in cases of diffuse sclerosis. With regard to the front-tap contraction, its discoverer150 admits that it may be obtained in persons in whom there is no reason to suspect organic disease. It is significant only when unequal on the two sides.
149 By extension the approximation of the dorsal surface to the tibial aspect of the leg —what some German writers call dorsal flexion—is meant.
150 Gowers, The Diagnosis of the Diseases of the Spinal Cord, 3d ed., p. 33.
In severe cases contractures are developed in the affected muscular groups, being, as a rule, preceded by the rigidity, increased reflex excitability, and the thereon dependent phenomena above detailed. These contractures may be like those of spastic paralysis, but usually the adductors show the chief involvement, and sometimes the leg becomes flexed on the thigh and the thigh on the abdomen in such firm contraction that the patient, albeit his gross motor power is not sufficiently impaired, is unable to move about, and is confined to his bed, his heel firmly drawn up against his buttock. It is stated by Leyden that the contracted muscles occasionally become hypertrophied—an occurrence I have not been able to verify. As a rule, some muscular groups are atrophied, though the limbs as a whole, particularly in those patients who are able to walk about, are fairly well nourished.
Pain in the back is a frequent accompaniment of diffuse sclerosis. It is not pronounced, but constant.
The drift of opinion to-day is to regard pain in the spinal region as not pathognomonic of organic spinal affections. It is true that pain is a frequent concomitant of neuroses, and that it is more intense and characteristic in vertebral and meningeal disease; but in denying a significance to pain in the back as an evidence of diffuse disease of the cord itself, I think many modern observers have gone to an extreme. It is particularly in diffuse sclerosis that a dull heavy sensation is experienced in the lumbo-sacral region; and in a number of my cases of slowly ascending myelitis and of tabes dorsalis the involvement of the arms was accompanied by an extension of the same pain, in one case associated with intolerable itching, to the interscapular region. It cannot be maintained that the pain corresponds in situation to the sclerotic area. It is probably, like the pain in the extremities, a symptom of irradiation, and corresponds in distribution to that of the spinal rami of the nerves arising in the affected level.
As the posterior columns are usually involved in transverse myelitis, the same lancinating and terebrating pains may occur as in tabes dorsalis. As a rule, they are not as severe, and a dull, heavy feeling, comparable to a tired or a burning sensation, is more common. A belt sensation, like that of tabes, and as in tabes corresponding to the altitude of the lesion, is a much more constant symptom than acute pains.
Cutaneous sensibility is not usually impaired to anything like the extent found in advanced tabes. It is marked in proportion to the severity of the motor paralysis; where mobility is greatly impaired, profound anæsthesia and paræsthesia will be found; where it is not much disturbed, subjective numbness, slight hyperæsthesia, or tingling and formication may be the only symptoms indicating sensory disturbance; and there are cases where even these may be wanting.
The visceral functions are not usually disturbed. In intense transverse sclerosis of the upper dorsal region I observed gastric crises, and in a second, whose lesion is of slight intensity, but probably diffused over a considerable length of the cerebro-spinal axis, there is at present pathological glycosuria. The bladder commonly shows slight impairment of expulsive as well as retaining power, the patients micturating frequently and passing the last drops of urine with difficulty. Constipation is the rule. The sexual powers are usually diminished, though rarely abolished. As with sclerotic processes generally, the sexual functions of the female, both menstrual and reproductive, are rarely disturbed.
It is not necessary to recapitulate here the symptoms which mark diffuse sclerosis at different altitudes of the cord. With this modification, that they are less intense, not apt to be associated with much atrophic degeneration, nor, as a rule, quite as abruptly demarcated in regional distribution, what was said for acute myelitis may be transferred to this form of chronic myelitis. The progress of diffuse sclerosis is slow, its development insidious, and the history of the case may extend over as long a period as that of diffuse
sclerosis. Sooner or later, higher levels of the cord are involved in those cases where the primary focus was low down. In this way the course of the disease may appear very rapid at one time, to become almost stationary at others. Of three deaths which occurred from the disease in my experience, one, in which there were distinct signs of involvement of the oblongata,151 occurred from sudden paralysis of respiration; a second from a cardiac complication, which, in view of some recent revelations concerning the influence of the tabic process on the organic condition of the valves of the heart, I should be inclined to regard as not unconnected with the sclerosis; and in a third, from bed-sores of the ordinary surgical variety. The malignant bed-sore is not of frequent occurrence in this disease.
151 On one occasion the patient had momentary anarthria, followed a day later by two successive periods of anarthria, lasting respectively about twenty seconds and one minute, one of which was accompanied by diplopia of equally brief duration.
PROGNOSIS.—The disease may, as in the instances cited, lead to a fatal termination, directly or indirectly, in from three to twenty years. The average duration of life is from six to fifteen years, being greater in cases where the sclerotic process is of slight intensity, even though it be of considerable extent, than where it is of maximum or destructive severity in one area, albeit limited. I am able to say, as in the case of tabes dorsalis, that a fair number of patients suffering from this disease whom I have observed for from two to six years have not made any material progress in an unfavorable sense in that time. One cure152 occurred in this series, of a patient manifesting extreme contractures, atrophies, bladder trouble, and ataxiform paresis, where the cause was plainly syphilis, and the histological character of the lesion is somewhat a matter of conjecture in consequence. Diffuse sclerosis of non-syphilitic origin—and this may apply also to established sclerosis in syphilitic subjects—is probably as unamenable to remedial treatment as any other sclerotic affection.
152 The patient went, under direction of Leonard Weber and R. H. Saunders, to Aixla-Chapelle, where this happy result was obtained after mixed treatment had
practically failed.
The same rules of DIAGNOSIS applicable to transverse myelitis of acute onset apply, level for level, to the diagnosis of transverse myelitis of insidious development, the history of the case often furnishing the only distinguishing point between the acute and the chronic form.
The main difference between the diffuse sclerosis and acute myelitis, clinically considered, consists in the gradual development of symptoms in the former as contrasted with their rapid development in the latter disease. Acute myelitis is established within a few hours, days, or at most, in the subacute forms, a few weeks; chronic myelitis requires months and years to become a clearly-manifested disorder. It is the essential correspondence of the symptoms of both conditions, intrinsically considered, which renders it impossible to distinguish clinically and in the absence of a history of the case between some cases of acute myelitis in the secondary period and the processes which are primarily of a sclerotic character.
It is unusual to find the degeneration reaction in myelitis of slow and gradual development. Sometimes there is diminished reaction to both the faradic and galvanic currents, or the so-called middle form of degeneration reaction is obtained from atrophied muscles, the nerve presenting normal or nearly normal irritability, and the muscle increased galvanic irritability and inversion of the formula.
Among the less reliable or accessible points of differentiation between the residua of acute myelitis and the chronic form is the history of the onset and the age of the patient at the time of the onset. Myelitis in young subjects is more likely to be of the acute kind; in older persons it is more apt to be chronic.
In the diagnosis of diffuse sclerosis the question of differentiation from neuroses not based on ascertainable structural disease, such as are called functional, will be most frequently raised. In differentiating between organic and functional spinal disorders all known exact signs of organic disease must be excluded before the
case can be considered as appertaining to the latter group. Symptoms of hysteria, nervous exhaustion, and spinal irritation frequently coexist with diffuse sclerosis as well as with the disseminated form; and this is not surprising, for, instead, as seemed at one time to be believed, of the neurotic taint granting comparative immunity against organic disease, it is the reverse, and it is not at all uncommon to find a strongly-marked neurotic diathesis in the family history of sufferers from diffuse sclerosis. That ordinary hysteria, epilepsy, and what is vaguely called nervousness are common features in the ancestral record of the hereditary forms of spinal disease has already been stated in considering those affections.
One of the commoner forms of the grave phase of hysteria is paraplegia.153 Often muscular atrophy—which ensues from disuse— exaggeration of the deep reflexes, and retention of urine are added to the paraplegia and heighten the resemblance to an organic affection. Its development, though sometimes sudden, often occupies weeks or months, and may be preceded, exactly as in chronic myelitis, by weakness in the legs, and not infrequently by combined ataxia and weakness. It is much more difficult to discriminate here than is generally held or than is enunciated in textbooks. The sufferer from hysterical paraplegia does not always give other indications of the hysterical neurosis, and even if she did show a globus and tenderness at certain points, it is a question whether it could be called a scientific diagnosis which determined the case to be one of functional trouble on these signs alone. More than one error has been committed in this respect. In chronic myelitis retention of urine is less common than incontinence, which is the reverse of hysterical paraplegia. Pupillary symptoms do not occur with the latter affection. If there be sensory anæsthesias, they are bizarre in character or distribution, and do not usually harmonize with the distribution of the paralysis. In most cases moral influences can be exerted so as to increase the power of movement far beyond what would be possible in an organic disease; and while an electrical examination will not always yield positive results in chronic myelitis, yet no case of chronic myelitis with complete or nearly complete
paraplegia but will show at least quantitative changes of such extent as to prove beyond doubt that the case is of an organic character.
153 I have observed for two years a stationary brachial diplegia, of undoubted hysterical origin, although the patient had never shown any ordinary hysterical manifestations, and had had no other hysterical symptom than chromatopsia, and that only for a short period. From its long duration, constancy, and the resulting atrophy of disuse it had been regarded as a case of peculiarly limited chronic myelitis.
There is one point in which spinal and cerebral disease involving the motor tract differs in the majority of cases, which may be utilized in distinguishing obscure affections of the former from those of the latter kind. In cerebral paralysis of any standing the superficial reflexes, such as the cremaster and abdominal reflexes, are usually diminished or abolished, while the deep or tendon reflexes are exaggerated. In spastic conditions due to spinal disease—say sclerosis of any kind affecting the lateral column and leaving the motor nuclei of the anterior cornua unaffected—the deep reflexes are similarly increased, but the cremaster reflex is increased also.154 This feature of the superficial reflexes is significant in the case of cerebral disease only when unilateral.
154 Attention has been called, I believe, by Westphal, to the fact that the cremaster reflex may not be demonstrable when reflex excitability is at its highest, because the cremaster muscle is already in extreme spastic contraction.
The initial period of diffuse sclerosis is sometimes confounded with rheumatism—an error less pardonable than in the case of tabes, inasmuch as in diffuse sclerosis the pains are not usually premonitory, but associated with motor paresis. It is erroneous to regard a pain as rheumatic because it is aggravated or relieved by changes in the weather. There are many subjects of myelitis who regard themselves as veritable barometers, and with more justice than most rheumatic patients.
In some cases of chronic alcoholism there are motor weakness and a gait much like that of diffuse sclerosis.155 It is to be remembered that the solar tickling reflex is very often abolished in alcoholic
subjects, and profound diminution of the normal cutaneous sensibility of the leg and feet usually coexist. But unless there is peripheral neuritis—which is an exceptional and, when present, wellmarked affection—the absence of profound nutritive changes of the muscle, the presence of the alcoholic tremor, the absence of sphincter and bladder trouble, and the great variation of the symptoms from week to week, and even from day to day, serve to distinguish the alcoholic spinal neurosis from myelitis.
155 Wilks' alcoholic paraplegia.
The Secondary Scleroses.
In studying the lesions underlying the symptoms of organic spinal disease, the occurrence of fascicular scleroses, secondary to such disease and due to the destructive involvement of nerve-tracts, was repeatedly noted. Türck may be regarded as the discoverer of these degenerations, and the reliability of this old observer may be inferred from the fact that one bundle of fibres liable to individual degeneration still goes by his name, and that, as far as he was able to discriminate between the various paths which secondary degenerations follow through the cerebro-spinal fibre-labyrinth, his statements have not been materially modified by more recent investigators, such as Bouchard, Vulpian, and Westphal.
The discovery by Meynert that the great cerebro-spinal tracts attain the white color which they owe to the development of myelin around their component axis-cylinders with advancing maturity, and that the tracts of noblest, and therefore most intelligent, function were the last to show this sign of maturity, was greatly extended by Flechsig, who found that each tract receives its myelin at a definite period of intrauterine life, the lowest or the nerve-roots first; then the short or intersegmental or—as the physiologist may call them—the automatic tracts; then the long or controlling tracts; and last, the associating tracts of the cerebral hemispheres which mediate the complex
relations underlying mental action. It was this discovery which gave a new impulse to the study of the secondary affections of the cord and brain. The accuracy with which secondary degeneration follows the lines marked out by the normal course of the tract is as great, diminishing when the tract diminishes, changing its position or direction and decussating where the latter changes its direction or position or decussates, that it constitutes not alone an interesting subject for pathological study, but has become one of the most reliable guides of the cerebral anatomist. It is of great importance to the pathologist to be able to differentiate between the primary disease and its secondary results, and, as the controversy concerning the so-called system diseases shows, even the most studious observers are uncertain in this direction in many cases.
MORBID ANATOMY.—Secondary degeneration manifests itself by a discoloration of the affected nerve-tract, which accurately corresponds in area to the normal area of that tract. The more recent the degeneration the less pronounced is this change. In advanced cases the color may be a dark gray, in moderately old ones a reddish or yellowish gray, and in those of very recent origin no change may be visible to the naked eye. It is claimed, however, that even here a loss of translucency of the white substance, giving it a sort of cheese-like opacity, may be detected. On hardening the specimen containing the degenerated tract in Müller's fluid or a simple bichromate salt solution, the affected area, instead of appearing dark on section in contrast with the gray substance—which in such preparations appears yellowish or a light brown—contrasts with the former by its lighter tinge. This contrast is observable even in cases where the naked eye was unable to detect the change in the fresh specimen. It can be sometimes found as early as the tenth day after the primary lesion, and is apparently simultaneously developed in the whole length of the nerve-tract affected.
The minute changes characterizing secondary degeneration begin in the essential conducting elements, the axis-cylinder, which exhibits a finely granular or molecular disintegration, and disappear. According to Homén, it shows an initial swelling and a failure to stain properly
before this. The myelin then follows suit: it becomes fragile, forms variously-shaped globules, and also disappears, and together with this a nuclear proliferation is noticed in the interstitial substance; fatty granule-cells are observed in large numbers, and manifest a tendency to accumulate in the perivascular districts. These cells are not permanent; their gradual diminution is accompanied by a proliferation of the interstitial tissue, which ultimately appears as a pure connective substance composed of fine fibrillæ arranged in undulating bundles. The entire process may be not inaptly compared to an hypertrophy of the interstitial substance resulting from overfeeding of its cellular elements by the morbid pabulum furnished through the disintegration of the nervous substance proper.
The disappearance of the nerve-tubes, and the formation of a new tissue in their place, which, like all tissues of the same character, undergoes shrinkage, leads to considerable deformity in the shape of the part which is the site of secondary degeneration. This is seen in the accompanying figure, where in an old-standing secondary degeneration of one interolivary layer the corresponding half of the medulla is greatly reduced in diameter as compared with the other side (Fig. 34), and the entire raphé is distorted. When one side of the cord is the site of such a change a similar asymmetry results.
FIG. 34.
Secondary Degeneration of Interolivary Layer: D Ds D, degenerated area; r, the distorted raphé.
According as the original lesion is incompletely or completely destructive, a larger or fewer number of axis-cylinders may be found preserved in the sclerotic tissue. It is not yet determined whether in some instances these fibres may not represent an admixture from another source than are comprised in the mainly affected tract.
Secondary degenerations are classified as ascending and descending. An ascending degeneration is one which is found situated brainward of the primary lesion; a descending one is found caudad of the lesion. It was once maintained that the direction of the secondary degeneration was constant for each individual tract. This seems to be true for a few. Some tracts, particularly in the brain, degenerate on both sides of the lesion, as I showed with regard to the interolivary layer.
The best studied form of secondary degeneration is that of the voluntary motor conduit known as the pyramid tract. Beginning in the so-called motor area of each cerebral hemisphere, the Rolandic loop
passes into the anterior part of the posterior half of the internal capsule, to be thence continued through the crus, pons, and the pyramids of the oblongata to the decussation or crossing-point of the pyramids. Here the greater part of the tract crosses into the opposite lateral column, occupying the position described in the section on Spastic Paralysis. A smaller part remains on the same side of the continuous interpyramidal and ventro-spinal fissure, constituting the direct fasciculus of Türck.
The crossed-pyramid tract diminishes as it passes caudad in the cord, giving off its fibres to the lateral reticular processes of the cord, whence—whether interrupted by cells (Von Monakow) or not—they probably reach the great cells in the gray substance from which the anterior rootlets spring. The direct fasciculus probably terminates in a similar way, and perhaps makes good, as it were, its failure to participate in the gross decussation at the level of the foramen magnum by decussating in detail along its entire length. It is usually exhausted before the lumbar cord is reached, whereas the crossed tract in the lateral column continues down as low as the origin of the sacral nerves. A destructive lesion anywhere in the course of the pyramid tract, whether it be in the motor area of the cortex, in the loop of Rolando, in the internal capsule, the pons, or the cord itself, will provoke descending degeneration; that is, sclerosis of so much of the tract as lies below the lesion. Thus such degeneration is found with porencephalic defect of the motor area. I found it in a paretic dement who had extensive cortical destruction following a submeningeal hemorrhage. It has been observed after focal lesion of the pons (Homén, Schrader), and after transverse lesions of the cord, either myelitic, traumatic, or as the result of compression by vertebral disease. As a rule, the cells in the anterior horn are not involved, and some observers question whether this ever occurs. I have never found such involvement, although in its gross dimensions the anterior horn as a whole appears atrophied. This atrophy I have been able to account for satisfactorily by the disappearance of many of the fibres which run into the gray substance from the reticular processes.
While the distribution of degeneration in the cord is rather uniform, varying only in harmony with the ascertained individual variations in the relative preponderance of the crossed and uncrossed parts of the pyramid tract, there is much more variation in the cerebral distribution of the degeneration according to the extent of the original lesion. Thus, if the entire capsule be destroyed, the greater part of the crus is involved. If only the posterior division in its anterior part be destroyed, the degeneration is in the crus, limited to that part which runs a subpial course on the crural demi-cylinder, occupying from a fifth to a third of its surface-area. Still more limited degenerations are described, but as yet are too few in number to base other than tentative conclusions on them. Among these is one occupying a thin strip on the inner side of the crus, which degenerates after lesions near the genu of the capsule, and probably represents the tract which governs the cranial nerve-nuclei. An excellent observation by Von Mannkopf shows that the course of the motor fasciculus is subject to some individual variation even within the capsule.
A number of forms of secondary degeneration are described, involving intracerebral tracts, such as those connecting the cerebrum and cerebellum. The degeneration of the visual tract, from the optic nerve to the occipital lobe, observed by Richter and Von Monakow, with some conflict of opinion between these observers, is often as perfectly demonstrative of the course of the optic fasciculi as degeneration of the pyramid tract is demonstrative of the course of the voluntary innervation of the muscles moving the limbs.
The secondary degenerations following lesion of the pons varolii are acquiring special interest in view of their relation to special nervetracts of the spinal cord of hitherto unknown function. The purest instance of an isolated degeneration of other than the pyramid tract is the case illustrated in the accompanying diagrams. It involved the interolivary layer, was both ascending and descending, being traced above into the subthalamic region, and below decussating into the opposite side of the oblongata, to terminate in the nuclei of the