Pulsed Electrical Discharge in Vacuum

1. Introduction.- 2. Review of Vacuum Breakdown and Discharge Studies.- 2.1 The Electrode Surface in a Vacuum Discharge.- 2.1.1 Preparation of Electrodes.- 2.1.2 Determination of Micropoint Parameters.- 2.1.3 Effect of Emission from Non-metallic Inclusions.- 2.2 Vacuum Insulation, Properties and Breakdown.- 2.2.1 Prebreakdown Phenomena.- 2.2.2 Microdischarges.- 2.2.3 The Breakdown Voltage.- 2.3 Kinetics of Vacuum Electrical Breakdown.- 2.3.1 Characteristic Times of Breakdown.- 2.3.2 Role of Electrodes in the Development of Breakdown.- 2.3.3 X-Ray Pulse at Breakdown.- 2.4 Field Electron Emission to Vacuum Breakdown Transition.- 2.5 Hypotheses on Vacuum Breakdown Initiation.- 2.5.1 Physical Processes Leading to Vacuum Breakdown.- 2.5.2 Cathode-Initiated Breakdown.- 2.5.3 Anode-Initiated Breakdown.- 2.5.4 Comparison between Cathode and Anode Mechanisms for Breakdown Initiation.- 2.5.5 Microparticle-Initiated Breakdown.- 2.6 Spark Stage of Vacuum Breakdown.- 2.7 The Discharge Arc Stage. The Cathode Spot.- 2.7.1 Physical Properties of the Cathode Spot.- 2.7.2 Cathode-Spot Models.- 3. Experimental Equipment and Techniques.- 3.1 Electrical Measurement Techniques.- 3.1.1 High-Voltage, Nanosecond Pulse Generators.- 3.1.2 Current and Voltage Pulse Recording.- 3.2 Diagnostics of the Radiation that Accompanies Breakdown.- 3.2.1 Electro-optical Recording of the Light Emission.- 3.2.2 Photoelectrical Recording of the Light Emission.- 3.2.3 Spectral Investigation of the Discharge Plasma Radiation.- 3.2.4 X-Radiation Recording.- 3.3 Vacuum Equipment.- 3.4 Preparation and Examination of Electrode Surfaces.- 4. Pulsed Nanosecond Breakdown of Vacuum Gaps.- 4.1 Time Characteristics of the Pulsed Vacuum Breakdown.- 4.1.1 The Influence of Electrode Conditioning.- 4.1.2 The Influence of the Vacuum.- 4.2 Study of Light Emission at Pulsed Breakdown.- 4.2.1 Single-Shot Investigations.- 4.2.2 The Continuous-Operation Regime.- 4.2.3 Comparison with Other Data.- 4.3 Electrode Erosion Studies.- 4.3.1 Cathode Erosion.- 4.3.2 The Tracer Method.- 4.3.3 Anode Erosion.- 4.4 Nature of the Discharge Current at Breakdown.- 4.5 Mechanism of Pulsed Breakdown of Vacuum Gaps.- 4.5.1 The Role of the Cathode.- 4.5.2 The Cathode Plasma and the Electron Current.- 4.5.3 Anode Phenomena.- 5. Cathode Processes in a Pulsed Vacuum Discharge.- 5.1 EEE Initiation by High-Density FEE Current.- 5.1.1 Experimental Conditions.- 5.1.2 Description of EEE Current.- 5.1.3 The Point Explosion Delay Time.- 5.1.4 Calculation of the Emitter Heating.- 5.1.5 The Vacuum Discharge Delay Time.- 5.2 Erosion of Point Cathodes.- 5.2.1 The Fast Current Rise.- 5.2.2 The Slow Current Rise.- 5.2.3 The Point Erosion Rate.- 5.2.4 Erosion Due to Joule Heating.- 5.2.5 Comparison with Experiment.- 5.3 EEE Current Density Measurements.- 5.3.1 Current Density of a Point Cathode.- 5.3.2 Current Density from a Massive Cathode.- 5.3.3 Measurements Based on Erosion.- 5.3.4 Experimental Data.- 5.4 Microstructure of the Cathode Surface.- 5.4.1 Erosion Traces in SEM.- 5.4.2 The Field Enhancement Factor.- 5.5 The Contribution of Droplet Ejection to Cathode Erosion.- 5.6 Pressure in the Emission Zone.- 5.7 Formation of Cathode Microstructure.- 6. Cathode Flare Plasma.- 6.1 Velocity of CF Plasma Expansion.- 6.1.1 The Grounded Grid and Collector Method.- 6.1.2 The Photoelectric Method.- 6.1.3 The Transverse Magnetic Field Method.- 6.1.4 The Method of the Anode Erosion Mark.- 6.2 CF Plasma Parameters.- 6.2.1 CF Plasma Density.- 6.2.2 CF Plasma Composition and Temperature.- 6.3 EEE Current Effect on the Dynamics of the Plasma Light Emission.- 6.4 A Model for CF Plasma Expansion.- 6.4.1 The Adiabatic Model.- 6.4.2 MHD Calculation.- 6.4.3 The Model of an Ideal Plasma.- 7. Current Passage in the Spark Stage of Breakdown.- 7.1 Electron Emission from CF Plasma into Vacuum.- 7.2 Electron Emission from CF Plasma, Experimental Studies.- 7.3 Current-Voltage Characteristics of a Single-CF Diode.- 7.4 Dynamics of the CF Electron Emission Boundary.- 7.5 CF Plasma Potential Distribution and Plasma Emissive Properties.- 7.5.1 Probe Measurements of the CF Plasma Potential.- 7.5.2 The Nature of the Instability of CF Emission.- 7.6 Spark Current Between Broad-Area Electrodes.- 7.6.1 Calculation of the Spark Current Rise.- 7.6.2 The Role of Cathode and Anode Flares.- 8. Formation of New Emission Centers on the Cathode.- 8.1 Mechanisms of New EC Formation Under the Plasma.- 8.1.1 Mechanism of the Explosion of Micropoints.- 8.1.2 Mechanism of the Explosion of the Liquid Neck.- 8.1.3 Mechanism of the Breakdown of Non-metallic Inclusions.- 8.2 New EC Formation and Operation Under Cathode Plasma.- 8.2.1 Experiments Without Application of a Magnetic Field.- 8.2.2 Effect of Transverse Magnetic Field on New EC Formation.- 8.2.3 Results and Discussion.- 8.3 "Screening" Effect and Electron Beam Structure in a Diode.- 8.3.1 "Screening" Effect.- 8.3.2 Influence of Neighbouring CFs on the Electron Beam Structure in the Diode.- 9. Anode Processes in the Spark Stage of Vacuum Breakdown.- 9.1 Anode Heat Conditions.- 9.1.1 Power Density Deposited at the Anode.- 9.1.2 The Anode Temperature.- 9.2 Surface Structure of the Anode in the Discharge Zone.- 9.2.1 Summary of Previous Work.- 9.2.2 Metallographic Studies.- 9.2.3 Electron-Microscopic Studies.- 9.2.4 Mechanisms of the Anode Surface Damage.- 9.3 Formation of Anode Flares.- 9.3.1 Conditions for AF Formation, Its Composition and Temperature.- 9.3.2 The Expansion Velocity of AF.- 9.4 X-Radiation Generated at the Anode.- 9.4.1 X-Radiation on Discharging a Line.- 9.4.2 X-Radiation on Discharging a Capacitor.- 10. Fast Processes at DC Breakdown of Vacuum Gaps.- 10.1 Electrical Study of DC Breakdown.- 10.1.1 Electric Circuit.- 10.1.2 Prebreakdown Current and Breakdown Voltage.- 10.1.3 The Current Rise Time at Breakdown.- 10.1.4 X-Radiation and Electrode Erosion at Breakdown.- 10.2 Optical Studies.- 10.2.1 Determination of the Time of Appearance of Light.- 10.2.2 Electro-optical Breakdown Studies.- 10.3 Comparison with Results of Other Investigations.- 10.4 EEE Initiation at DC Breakdown.- 10.4.1 EEE Initiation under Pure Conditions.- 10.4.2 EEE Initiation and the Total Voltage Effect.- 10.4.3 Criteria for Vacuum Breakdown and EEE Initiation.- 11. Nonstationary Processes in the Vacuum Arc Cathode Spot.- 11.1 The Motion of Vacuum Arc Cathode Spots.- 11.1.1 The Effect of Surface Condition.- 11.1.2 The Influence of a Magnetic Field.- 11.1.3 Spontaneous Formation of Cathode Spots in Pulsed Arc Discharges.- 11.2 Response of the Vacuum Arc to Current Transients.- 11.2.1 Experimental Equipment and Technique.- 11.2.2 Results.- 11.3 Vacuum Arcs at Threshold Currents.- 11.3.1 The Threshold Current of a Vacuum Arc.- 11.3.2 Cathode Spot Current Density.- 11.4 Numerical Simulation of Processes in an Explosive Emission Center.- 11.5 Explosive Electron Emission and the Vacuum Arc Cathode Spot.- 12. Pulsed Electrical Discharge in Vacuum at Cryogenic Electrode Temperatures.- 12.1 Field Electron Emission at Low Cathode Temperatures.- 12.1.1 Effect of Superconductivity on FEE Current.- 12.1.2 The Nottingham Effect and Superconductivity.- 12.1.3 Other Emission Effects.- 12.2 Field Emission Current Preceding the Explosion of a Point.- 12.3 Characteristics of the Vacuum Discharge at Cryogenic Temperatures.- 12.3.1 Experimental Conditions.- 12.3.2 Experimental Results.- 12.4 Vacuum Discharge Between Electrodes Made of High-Temperature Superconductors.- 12.4.1 General Notions.- 12.4.2 FEE from High-Temperature Superconducting Cathodes.- 12.4.3 Vacuum Discharge.- References.