Physics and Applications of Hydrogen Negative Ion Sources

Preface
	References
Contents
Contributors
1 Fundamental Processes of Hydrogen Negative Ion Production in Ion Source Plasma Volume
	1.1 Need of Negative Ion Beams for Magnetic Confinement Fusion Research and for High Energy Accelerators
	1.2 The Volume Production Mechanism
		1.2.1 Early Direct Extraction Negative Ion Sources (Before 1980)
		1.2.2 Observation of a New H− Ion Formation Mechanism in the Plasma Volume
		1.2.3 H− Formation by DA to Excited H2 Molecules
		1.2.4 Excited H2 Populations in Low-Temperature Plasmas
		1.2.5 Experimental Validation of the Volume Production Mechanism
	1.3 Volume Production of H− Ion Sources
		1.3.1 Penning Source
		1.3.2 The Magnetically Filtered Multicusp Volume Negative Ion Source
			1.3.2.1 Role of the Magnetic Filter
			1.3.2.2 Role of the Plasma Electrode
	1.4 Conclusion
	References
2 Fundamental Aspects of Surface Production of Hydrogen Negative Ions
	2.1 Introduction
		2.1.1 Early Observations
		2.1.2 High-Current Surface Plasma Source
		2.1.3 Cs Operation of Volume Production Source
	2.2 Mechanism of Negative Ion Surface Production
		2.2.1 Theoretical Background
		2.2.2 Experiments on Fundamental Processes
		2.2.3 Experimental Results Using Ion Sources
	2.3 Surface H− Ion Production at Low Energy
		2.3.1 Negative Ion Production at Cs Covered PG Surface
		2.3.2 Contamination of PG Surface by Impurities
	2.4 Conclusion
	References
3 Modeling of Reaction Dynamics in Volume-Production Negative Hydrogen Ion Sources
	3.1 Introduction
	3.2 Brief Description of GMNHIS
		3.2.1 Particle Balance Equation
		3.2.2 Power Balance Equation
		3.2.3 Chemistry Mechanism in the Volume-Production NHIS
	3.3 Benchmarking of GMNHIS for RF Discharge
		3.3.1 Negative Hydrogen Ion Density and Electronegativity Versus Pressure
		3.3.2 Electron Temperature and Electron Density Versus Pressure
		3.3.3 VDFs at Two Different Pressures
		3.3.4 Densities of Positive Ions and H (N == 1–3) Atoms Versus Pressure
	3.4 Validation of GMNHIS for ECR Discharge
		3.4.1 Electron Density Versus Pressure
		3.4.2 Pressure Dependence of VDF
		3.4.3 Determination of Negative Hydrogen Ion Density
		3.4.4 Production and Loss Mechanisms of Negative Hydrogen Ions
	3.5 Analytical Model for VDF
		3.5.1 Reduced Set of Processes for Vibrational Kinetics
		3.5.2 Particle Balance for Vibrational States
		3.5.3 Repopulation Probabilities of Vibrational States on the Wall
		3.5.4 Reduced Linear Model for VDF
	3.6 Conclusion
	References
4 Particle-In-Cell Modeling of Negative Ion Sources for Fusion Applications
	4.1 Introduction
	4.2 The Particle-In-Cell Technique
	4.3 Plasma Transport Across the Magnetic Barrier
	4.4 Gas Dynamics and Vibrational Kinetics
	4.5 Negative Ion Production on Surfaces
		4.5.1 2.5D of the Whole Ion Source Volume Including the Apertures
		4.5.2 Charged Particle Extraction Dynamics Across Apertures
	4.6 Conclusions
	Bibliography
5 Electrostatic and Electromagnetic Particle-In-Cell Modelling with Monte-Carlo Collision for Negative Ion Source Plasmas
	5.1 Fundamentals of Negative Ion Source Plasma Modelling by Particle-In-Cell
		5.1.1 Numerical Modelling for Negative Ion Source Development
			5.1.1.1 Main Physical Processes in Negative Ion Sources
		5.1.2 Basic Equations of the PIC Modelling
			5.1.2.1 Electrostatic PIC
			5.1.2.2 Electromagnetic PIC
		5.1.3 Collision Processes
	5.2 Negative Ion Extraction Mechanism from the Surface Production Ion Source
		5.2.1 Surface Produced H− Extraction Under the Low Source Filling Gas Pressure
		5.2.2 Surface-Produced H− Extraction Under the High Source Filling Gas Pressure
	5.3 Plasma Meniscus and Negative Ion Beam Optics
		5.3.1 Asymmetry of the Plasma Meniscus
		5.3.2 Effects of Extraction Voltage on the Plasma Meniscus and Beam Optics
		5.3.3 Negative Ion Beam Acceleration and Beam Optics
	5.4 EM-PIC-MCC Modelling in the RF Driven Negative Ion Source for Accelerators
		5.4.1 Introduction
		5.4.2 PIC Simulation of the E-Mode RF Plasma
		5.4.3 PIC Simulation of H-Mode RF Plasma
	5.5 Conclusion
	References
6 Plasma and Gas Neutralisation of High-Energy H− and D−
	6.1 Background
	6.2 Reactions
	6.3 Basic Equations
	6.4 Cross-Sections
	6.5 Calculation Method
	6.6 Results
	6.7 Discussion and Conclusions
	References
7 Advanced Models for Negative Ion Production in Hydrogen Ion Sources
	7.1 Introduction
	7.2 H2 Cross-Sections
	7.3 Numerical Model
	7.4 Global Kinetic Model of Multicusp Negative Ion Source
		7.4.1 Kinetic Scheme
		7.4.2 Multicusp Source
	7.5 Results
	7.6 Conclusions
	Bibliography
8 The Plasma Sheath in Negative Ion Sources
	8.1 Introduction
	8.2 The Plasma Sheath
	8.3 Production and Transport of Negative Ions Across the Sheath
		8.3.1 Surface Production of Negative Ions
		8.3.2 The Formation of a Virtual Cathode
		8.3.3 The Virtual Cathode in a Plasma-Based Ion Source
			8.3.3.1 The Sheath before the Formation of a Virtual Cathode
			8.3.3.2 The Plasma Sheath with a Virtual Cathode
	8.4 The Plasma Sheath with Negative Ions Emitted at the Wall
		8.4.1 The Sheath Structure and Its Implications
		8.4.2 The Effect of Surface Work Function
		8.4.3 The Emission of Electrons into the Sheath
	8.5 Beam Extraction
	8.6 Conclusions
	References
9 Helicon Volume Production of H- and D- Using a Resonant Birdcage Antenna on RAID
	9.1 Introduction
	9.2 The Resonant Antenna Ion Device (RAID)
		9.2.1 RAID Vacuum Vessel, Pumping System, and Magnetic Field
		9.2.2 RAID Plasma Source: The Birdcage Antenna
		9.2.3 Plasma Parameters in RAID and Standard Conditions
	9.3 Overview of RAID Diagnostics
		9.3.1 Diagnostics of Electron Parameters
		9.3.2 Diagnostics for Negative Ions: Optical Emission Spectroscopy, Cavity Ring-Down, and Photodetachment
			9.3.2.1 Optical Emission Spectroscopy (OES)
			9.3.2.2 Cavity Ring-Down Spectroscopy (CRDS)
			9.3.2.3 CRDS Experimental Setup in RAID
			9.3.2.4 Langmuir Probe Laser Photodetachment (LPLP)
	9.4 Measurements of Negative Ions
		9.4.1 First Evidence of Negative Ions in RAID Using OES
		9.4.2 Measurements of Negative Ions Using CRDS
		9.4.3 Measurements of Negative Ions with LPLP
		9.4.4 Combining CRDS and LPLP to Extract Absolute Negative Ion Density Profiles
	9.5 A 1.5D Fluid: Monte Carlo Model of a Hydrogen Helicon Plasma
		9.5.1 Description of the Fluid Model
		9.5.2 Reaction Rates
		9.5.3 A Monte Carlo (MC) Model to Determine Neutral Density Profiles
		9.5.4 Transport of the Ion Species
	9.6 Conclusions
	References
10 Plasma Electrode for Cesium-Free Negative Hydrogen Ion Sources
	10.1 Introduction
	10.2 Materials for Production of Highly Excited Ro-vibrational Hydrogen Molecules
	10.3 Materials for Negative-Ion Surface Production
		10.3.1 Basic Mechanisms of Negative-Ion Formation on Plasma Electrode Surfaces
		10.3.2 Carbon Materials
		10.3.3 Nanoporous C12A7 Electride
	10.4 Discussions and Summary
	References
11 Low-Temperature High-Density Negative Ion Source Plasma
	Nomenclature
	11.1 Introduction
	11.2 Magnetic Multipole Plasma Source and Its Filaments
	11.3 The Discharge Mechanism and the Ion Species Ratio
	11.4 Mode Flap in Arc Discharge
	11.5 Cusp Leak Width
	11.6 Need of Negative Ion Beams
	11.7 Negative Ion Production
	11.8 Volume Production
	References
12 ECR–Driven Negative Ion Sources Operating with Hydrogen and Deuterium
	12.1 Fundamental Principles of Electron Cyclotron Resonance (ECR) Heating
	12.2 H− and D− Negative Ion Production and Destruction Processes in ECR-Driven Plasmas
	12.3 Representative H− and D− Negative Ion Sources
		12.3.1 Camembert III
		12.3.2 Prometheus I
		12.3.3 ECR with Driven Plasma Rings
		12.3.4 HOMER
		12.3.5 ROSAE (I, II, and III)
		12.3.6 Scheme (I, II, and II+)
	12.4 Other Sources and Extracted Currents in ECR Sources
	References
13 Vibrational Spectroscopy of Hydrogen Molecules by Detecting H− (D−) and Its Use in Studies Relevant to Negative Ion Sources
	13.1 Introduction
	13.2 Dissociative Electron Attachment to Hydrogen
	13.3 Hydrogen Vibrational Spectroscopy (HVS) by Negative Ion Detection
		13.3.1 Basics of the Use of DEA Properties for Hydrogen Vibrational Spectroscopy (HVS)
		13.3.2 Experimental Setups
			13.3.2.1 Electrostatic Setup at LDMA Paris
			13.3.2.2 Magnetic Setup in JSI Ljubljana
			13.3.2.3 Beam-Like Experimental Setup in JSI Ljubljana
	13.4 Applications and Results
		13.4.1 Metal Cell with the Hot Tungsten Filament
		13.4.2 Atom Recombination on Metal Exposed to Atom Beam
		13.4.3 Results of Some Other Applications of HVS Based on DEA
	13.5 Perspectives
	References
14 Physics of Surface-Plasma H− Ion Sources
	14.1 Introduction
	14.2 Mechanism of Surface-Plasma Negative Ion Production
		14.2.1 Main Physical Processes in SPS
		14.2.2 First Surface-Plasma Sources
		14.2.3 Studies of Intense Negative Ion Production in the First SPS
	14.3 Surface Processes of Negative Ion Formation in SPS
		14.3.1 Negative Ion Secondary Emission
		14.3.2 H− Production by Hydrogen Particles Backscattering (Reflection)
			14.3.2.1 H− Production by Backscattering of Energetic Hydrogen Ions and Atoms
			14.3.2.2 H− Production by Backscattering of Thermal Hydrogen Atoms
			14.3.2.3 H− Production by Backscattering of Suprathermal Hydrogen Atoms
		14.3.3 Negative Ion Production by Desorption (Sputtering)
			14.3.3.1 Negative Ion Production Due to Impact Desorption by Light Ions and Atoms
			14.3.3.2 Negative Ion Production Due to Impact Desorption by Heavy Ions
			14.3.3.3 Total H− Ion Production by Backscattering and Desorption by Hydrogen Ions
		14.3.4 Negative Ion Yield Due to Mixed Ion Bombardment
		14.3.5 Surface Negative Ion Production in Plasma Environment
			14.3.5.1 Hydrogen-Cesium Plasma
		14.3.6 Hydrogen Plasma with Addition of Inert Gases
	14.4 Channels and Efficiency of Negative Ion Production in SPS
		14.4.1 SPSs with High-Current E = B Discharges
			14.4.1.1 Planotron (Magnetron) SPSs
			14.4.1.2 Penning SPSs
		14.4.2 Direct Current SPSs
		14.4.3 Multicusp SPS with Internal Converter
		14.4.4 SPSs with Pulsed High-Power RF Discharges
		14.4.5 Giant Long-Pulsed Multiaperture SPS for Fusion Neutral Beam Injectors
	14.5 Essential Features of Negative Ion Production in SPS
		14.5.1 Cesium Catalyst of Negative Ion Production
			14.5.1.1 Primary Cesium Seed to SPS Electrodes
			14.5.1.2 Conditioning (Activation) of the Cesiated SPS Electrodes
			14.5.1.3 Confinement and Recirculation of Cesium in the High-Current E = B Discharges
		14.5.2 Suppression of Co-extracted Electron Flux
	14.6 Summary
	References
15 Hydrogen Negative Ion Density Diagnostic in Plasma
	15.1 Introduction
	15.2 Measurement of the Negative Ion Density in Plasma by Langmuir Probe-Assisted Photodetachment
	15.3 Measurement of the Negative Ion Density in Plasma by Cavity Ring-Down Spectroscopy (CRDS)
	15.4 Negative Ion Source Study with Photodetachment Method
	15.5 Conclusion
	References
16 RF-Driven Ion Sources for Neutral Beam Injectors for Fusion Devices
	16.1 Introduction
	16.2 Modular Concept of the RF-Driven Ion Source
		16.2.1 The Prototype Source
		16.2.2 Size Scaling
		16.2.3 RF Coupling Efficiency
		16.2.4 Magnetic Filter Field
		16.2.5 Low Pressure Operation
		16.2.6 Plasma Parameter
	16.3 Achievements for ITER
		16.3.1 Short Pulses: Up to 10 s
		16.3.2 Long Pulses: Up to 1 h
		16.3.3 Toward Full Performance of the ITER Source: A Stepwise Approach
	16.4 Lessons Learned and Challenges
		16.4.1 Source Operation: RF Issues/Technology
		16.4.2 Plasma Uniformity, Symmetry of Co-extracted Electrons, and Beam Uniformity
		16.4.3 Cesiation and Co-extracted Electrons
	16.5 Activities Beyond ITER
		16.5.1 RF Sources for a DEMO: Worldwide Activities
		16.5.2 Racetrack-Shape RF Drivers
		16.5.3 Cesium Consumption
		16.5.4 Reliability and Availability
	16.6 Conclusion and Outlook
	References
17 Ion Source Engineering and Technology
	17.1 Introduction
	17.2 Powering the Plasma
		17.2.1 Accelerating Electrons
		17.2.2 CCP Power Supply
		17.2.3 ICP Power Supply
	17.3 Magnetic Fields
		17.3.1 Magnetised Electrons
		17.3.2 Making Magnetic Fields
	17.4 Extracting Negative Ions
	17.5 High Voltage
		17.5.1 High Fields
		17.5.2 High-Voltage Platform
		17.5.3 Platform Bias Voltage Stability
		17.5.4 High-Voltage Enclosure Versus High-Voltage Room
		17.5.5 High-Voltage Design
		17.5.6 Electrode Design
		17.5.7 Insulator Design and Triple Junctions
		17.5.8 Triple Junction Shielding
		17.5.9 Insulator Material
		17.5.10 Insulator Surface Profile
		17.5.11 Insulator Protection
		17.5.12 Insulation Coordination
		17.5.13 Gaseous Insulation
		17.5.14 Liquid Insulation
		17.5.15 Cooling Equipment on High-Voltage Platforms
		17.5.16 Breakdown Protection
	17.6 Earthing
		17.6.1 The Earth Connection
		17.6.2 Local Earth
		17.6.3 Earth Loops
		17.6.4 Equipotential Bonding
		17.6.5 Automatic Earthing
		17.6.6 Earth Sticks
	17.7 Safety
		17.7.1 Compliance with Regulations
		17.7.2 Personnel Protection Interlock System
		17.7.3 Reliability of the PPS
		17.7.4 IEC 61508
		17.7.5 Electrical Authorization
		17.7.6 Radiation Protection
		17.7.7 Hydrogen Safety
	17.8 Controls and Diagnostics
		17.8.1 Control System
		17.8.2 Diagnostics
	17.9 Vacuum and Gas Systems
		17.9.1 A Wide Range of Pressures
		17.9.2 Differential Pumping
		17.9.3 Vacuum System Design
		17.9.4 Trapped Volumes
		17.9.5 Types of Vacuum Flanges and Seals
		17.9.6 Primary Vacuum Vessel and Main Insulator
		17.9.7 Plasma Chamber
		17.9.8 Surfaces in Vacuum
		17.9.9 Vacuum System Exhaust
		17.9.10 Gas Delivery Systems
		17.9.11 Caesium Systems
	17.10 Plasma Ignition Systems
	17.11 Documentation Systems
		17.11.1 Mechanical Drawings
		17.11.2 Electrical Drawings
		17.11.3 Ancillary Equipment
		17.11.4 Ion Source `Build Sheets'
		17.11.5 Post Failure Analysis
	17.12 Reliability
	References
18 Radio Frequency-Driven, Pulsed High-Current H− Ion Sources on Advanced Accelerators
	18.1 Introduction
	18.2 Radio Frequency-Driven, Hydrogen Discharges
	18.3 The Spallation Neutron Source RF H− Ion Source
	18.4 The Surface-Produced H− Ions
	18.5 The Management of Cesium
	18.6 Refurbishing and Starting Up RF Ion Sources, Their Performance, and Their Plasma Outages
	18.7 Internal or External Antenna?
	18.8 Other Failures of the Past
	18.9 Service Cycles and Lifetimes of the SNS RF H− Source
	18.10 The H− Beam Decay and the Loss of Cesium
	18.11 Surface Films in the SNS RF H− Ion Source
	18.12 The SNS H− Extraction and the Low-Energy Beam Transport
	18.13 A Summary and Outlook for the SNS RF H− Ion Source
	18.14 The RF-Driven H− Source at J-PARC
	18.15 The RF-Driven H− Source at CERN's LINAC4
	18.16 The RF-Driven H− Source at CSNS
	18.17 The Future of Pulsed, High-Current H− Sources
	References
19 Development of High-Current Negative-Ion-Based Beam Source at the National Institutes for Quantum Science and Technology (QST) in Japan for JT-60 U and ITER Neutral Beam Injectors
	19.1 Negative Ions in Fusion Applications
	19.2 Magnetic Filter for Low-Temperature Plasma
	19.3 KAMABOKO Source for Surface Production of Negative Ions
	19.4 Negative Ion Extraction and Electron Suppression
	19.5 Beam Deflection and Compensation
	19.6 Negative Ion Acceleration up to MeV Beam Energy
	19.7 Conclusion and Discussion
	References
Postface
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