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DOE-tr-l

Draft

Thermionic Converters and Low-Temperature Plasma

By

F. G. Baksht, G. A. Dyuzhev, A. M. Martsinovskiy,

B. Ya. Moyzhes, G. Ye. Pikus, E. B. Sonin and

V. G. Yur’yev

Russian Edition edited by

B. Ya. Moyzhes and G. Ye. Pikus

English Edition edited by

Lorin K. Hansen

Prepared for

Division of Power Systems

Office of Fossil Energy Programs

U.S. Department of Energy

1978

Published by

Technical Information Center/U.S. Department of Energy

Russian edition published in 1973

Scanning and Editing:

Gary Owen Fitzpatrick

Editing:

Artemy Martsinovski

James Luke

Momozaki Yoichi

1998

V

Table of Contents

Preface to the Russian Edition iii

Foreword to the English Edition V

Page

CHAPTER l.THERMIONIC CONVERTERS AND LOW-TEMPERATURE PLASMA ...................1

1. Methods of Direct Conversion of Thermal to Electrical Energy............1

2. The Efficiency of Direct Conversion of Thermal to Electrical Energy.....4

3. The Main Operating Modes of Thermionic Converters (TICs)................5

4. The Efficiency and Power Density of a TIC...............................8

5. Requirements for Electrode Materials and TIC Designs...................10

6. Prospects for Using TICs...............................................12

7. The Plasma in a TIC....................................................13

References................................................................18

CHAPTER 2. EMISSION AND ADSORPTION PROCESSES(TIC ELECTRODES) ................19

1. Thermionic Emission....................................................19

2. Thermal Effects During Thermionic Emission.............................23

3. The Contact Potential Difference.......................................24

4. Thermionic Emission in an Accelerating Field...........................25

5. Evaporation............................................................27

6. Surface Energy.........................................................29

7. Adsorption and Its Effect on the Work Function.........................30

8. Surface Ionization.....................................................33

9. Adsorption of Cesium on Refractory Metals..............................34

10. Electropositive Additives in TICs.....................................39

11. Electronegative Additives in TICs.....................................42

12. The Vacuum Mode of TIC Operation......................................47

References................................................................52

CHAPTER 3. ELEMENTARY PROCESSES IN A PLASMA..................................55

1. Elastic Collisions.....................................................55

2. Coulomb Collisions.....................................................57

3. Elastic Electron—Atom Collisions.......................................59

4. Ion—Atom Collisions....................................................60

5. Inelastic Electron—Atom Collisions.....................................61

6. Classification of the Levels in the Atoms of Alkali Metals.............66

7. Radiation and Absorption of Light......................................69

8. Spectral Broadening....................................................73

References................................................................78

CHAPTER 4. KINETIC PHENOMENA IN THE PLASMA...................................81

1. The Kinetic Equation...................................................81

2. Solution of the Kinetic Equation in the Relaxation Time Approximation..84

3. Transport Equations and Kinetic Coefficients in the Relaxation Time Approximation. Electron Current and Electron Energy Flux in a Weakly Ionized Plasma......87

vii

4. The Effect of a Magnetic Field on Transport Phenomenon.................91

5. The Effect of Interelectrode Collisions and Ion Scattering on the Kinetic Coefficients for Electrons................................................95

6. Exchange of Energy and Momentum Between Electrons and the Heavy Components of a Plasma...................................................................104

7. The Kinetic Coefficients for Tons in a Weakly Ionized Plasma..........111

References...............................................................117

CHAPTER 5.IONIZATION AND RECOMBINATION IN A LOW-TEMPERATURE PLASMA.........119

1. A Plasma in Thermodynamic Equilibrium.................................119

2. Ionization and Recombination in a Plasma..............................123

3. Calculating the Rate of Ionization—Recombination by Solving the Equations of Particle Balance for the Excited Levels Ionization in a Cesium Plasma...................................................................134

4. Calculating the Radiation from the Plasma. The Effect of Radiation on the Rate of Ionization—Recombination in an Optically Dense Plasma. The Diffusion of Excited Atoms....................................................................142

5. The Effect of Inelastic Processes on the Free—Electron Distribution Function.................................................................149

References...............................................................163

CHAPTER 6. PRE-ELECTRODE PHENOMENA IN A TIC PLASMA..........................167

1. The Pre—Electrode Sheaths for a Plasma in Thermodynamic Equilibrium...167

2. Ion Flow from a Plasma and the Potential Distribution in the Pre-Electrode Sheath with Negative Voltage on the Electrode...................................170

3. Electron Flow at the Contact of the Plasma with a Negatively Biased Electrode................................................................181

4. Cathode Beam Relaxation in the Pre-Electrode Sheath of a Weakly Ionized Plasma...................................................................193

5. The Effect of a Non-Equilibrium Electron Distribution Function on the Rate of Atomic Ionization in the Pre—Electrode Sheath............................202

6. Electron Flow From the Plasma and Potential Distribution With a Positive Potential Applied to the Electrode.................................................204

7. Approximate Boundary Conditions for the Transport Equations in a TIC..208

References...............................................................217

CHAPTER 7. EXPERIMENTAL METHODS FOR INVESTIGATING LOW-TEMPERATURE PLASMAS....221

1. Probe Diagnostics of Plasmas..........................................221

2. The Use of Probes in TICs.............................................239

3. Optical Methods for Determining the Plasma Parameters of a TIC........245

4. Comparison of the Probe and Spectral Methods..........................255

5. Design of Experimental Devices. Boundary Effects......................259

References...............................................................263

Viii

CHAPTER 8. THE DIFFUSION MODE OF THERMIONIC CONVERTERS......................267

1. The Theory of the Diffusion Mode......................................267

2. The Characteristics and Properties of a Diffusion Plasmas.............279

3. The Effect of Magnetic Fields on the Diffusion Mode...................287

References...............................................................292

CHAPTER 9. THE LOW-VOLTAGE ARC IN A TIC......................................293

1. The Main Equations Which Describe the State of the Arc Plasma of a TIC.293

2. Boundary Conditions....................................................296

3. Methods for Calculating the State of the Plasma and the Current-Voltage Characteristic............................................................304

4. Local Thermodynamic Equilibrium........................................307

5. Deviation of the Electron Distribution Function Near the Cathode from a Maxwellian Distribution. Non-Equilibrium Ionization..................................317

6. Characteristics of the Low-Voltage Arc in a TIC........................321

7. Transition from a Diffusion to an Arc Mode.............................326

8. The Mode With Cathode Emission Limited by Space Charge (The Virtual Cathode)..................................................................333

9. The Increase of Current in the Developed Arc...........................336

10. The Effect of External Parameters on the Arc Mode.....................339

11. The Arc Mode With a Strongly Ionized Plasma...........................347

12. Variation of Atom and Ion Flow to the Cathode in the Arc Mode.........357

13. The Effect of Inert Oases on the Current-Voltage Characteristics......360

14. The Effect of Magnetic Field on TIC Operation in the Arc Mode.........365

15. Transient Processes in the TIC Arc Mode...............................366

References................................................................373

CHAPTER 10. THE DIRECT-FLIGHT (KNUDSEN) MODE OF TIC OPERATION................377

1. The Knudsen Mode TIC Operation with a Monotonic Potential Distribution in the Gap.......................................................................378

2. The Knudsen Mode of TIC Operation with a Non-Monotonic Potential Distribution in the Gap...................................................................384

3. Experimental Investigation of a Knudsen Plasma in a TIC................399

4. The Effect of a Magnetic Field on TIC Operation in the Direct—Flight Mode......................................................................403

5. The Knudsen Arc........................................................408

References................................................................419

CHAPTER 11. SOME ENGINEERING PROBLEMS OF TIC.................................423

1. Current—Voltage Characteristics........................................423

2. Prospects for Increasing TIC Output Parameters.........................426

3. The Reactor Converter..................................................428

4. Use of Heat Pipes......................................................436

5. Materials for a Reactor TIC............................................439

6. Reactor Tests for TICs.................................................440

7. TICs With Isotopic Heat Sources........................................445

ix

8. The Use of the TIC in Central Power Plant Engineering..................449

References................................................................450

APPENDICES

1. Some Physical Constants................................................453

2. Correlation of Some Physical Quantities for a Cesium Plasma............454

3. Some Emission Parameters...............................................455

4. Temperature Dependence of Thermionic Emission at Different Emitter Work Functions.................................................................456

5. Temperature Dependence of Equilibrium Electron Density at Different Cesium Vapor Pressures.................................................................457

6. Temperature Dependence of Chemical Potential at Different Cesium Vapor Pressures.................................................................458

SYMBOLS......................................................................459

INDEX........................................................................479

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