Inertial Electrostatic Confinement (IEC) Fusion

Transcription

1 Inertial Electrostatic Confinement (IEC) Fusion

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3 George H. Miley S. Krupakar Murali Inertial Electrostatic Confinement (IEC) Fusion Fundamentals and Applications

4 George H. Miley Fusion Studies Lab University of Illinois Urbana, IL, USA S. Krupakar Murali Department of Electronics and Communication Engineering J. K. K. M. College of Technology Erode District, TN, India ISBN ISBN (ebook) DOI / Springer New York Heidelberg Dordrecht London Library of Congress Control Number: Springer Science+Business Media New York 2014 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. Exempted from this legal reservation are brief excerpts in connection with reviews or scholarly analysis or material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Duplication of this publication or parts thereof is permitted only under the provisions of the Copyright Law of the Publisher s location, in its current version, and permission for use must always be obtained from Springer. Permissions for use may be obtained through RightsLink at the Copyright Clearance Center. Violations are liable to prosecution under the respective Copyright Law. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Printed on acid-free paper Springer is part of Springer Science+Business Media (

5 Preface This book is intended to provide the reader with an overview of the basics, the current experimental status, supporting theory and technology, and potential applications of Inertial Electrostatic Confinement (IEC) fusion. The IEC is a unique approach to fusion in that electrically driven units offer a number of near-term spin-off applications. This is largely due to its simple construction and ability to provide a relatively high fusion rate in a small volume, i.e., at a low power level. Such operation is four or five orders of magnitude below energy breakeven, but the application justifies the cost of the electrical input required to drive the fusion. Examples include a small neutron source for Neutron Activation Analysis (NAA) to determine impurities in ores or coal at the mine. Extension of that technology discussed in this book includes land mine detection, neutron radiography, clandestine material detection at air- and seaports, medical isotope production, plasma space propulsion, subcritical fusion fission hybrid reactors, and tunable x-ray sources, to name a few. The simplicity of the IEC has made construction of experiments, often called fusors, possible. A number of amateur scientists and high school students have built units in their garages. These garage-based fusor experiments typically used hydrogen or run at low voltages to avoid serious radiation (x-rays and neutrons) danger to the operator. These experiments are an important introduction to fusion for a number of young people, some of whom eventually make fusion science their careers. Devices with higher neutron rates have been studied at various universities and laboratories where radiation shielding and monitoring can be employed. Much of this work has been done in the United States and Japan and is documented in a long series of DOE-sponsored U.S. Japan IEC workshops. Principle participants have been the Universities of Illinois and Wisconsin, Los Alamos National Laboratory (LANL), Kyoto University, Kobe University, and the Tokyo Institute of Technology. Other participants include researchers from the University of Maryland, University of Sydney, University of Missouri, along with the private company EMC 2. Much of the material in this book comes from presentations at these meetings, with emphasis on IEC studies at the Universities of Illinois and Wisconsin, which the authors are most familiar with. v

6 vi Preface To move the IEC from electrically driven units to fusion breakeven and a power producing fusion plant requires a basic change from beam background neutral reactions to beam beam fusion. While studies of magnetically insulated and actively cooled grids have been performed, the preferable approach is to replace physical grids with virtual electrodes, forming a deep potential well for ion confinement. Indeed this is along the lines originally proposed by Philo Farnsworth (the U.S. inventor of electronic television) in his IEC patent which discussed poissors (virtual electrodes). The feasibility for experimentally achieving such a state revolves around fundamental physics issues such as ion beam thermalization, ion upscattering out of the well, stability of this configuration, and the ratio of ion to electron temperature (average energy). Much work remains to resolve these issues. Still, if such an IEC mode can be achieved, the door would be opened to a highly non-maxwellian fusion plant capable of using advanced fuels such as D 3 He and p 11 B as well as D T and D D. Due to its simple structure and theoretical capability to achieve breakeven and net power gain in small units, an experimental campaign to study this could be done faster and at much less cost than currently involved in the international effort to develop a Tokamak reactor based on magnetic confinement. This book reviews some computational/theoretical studies focused on moving toward an IEC power unit, but many issues need more study to fully understand the physics involved. On the other hand, electronically-driven gridded devices for immediate applications are reasonably well understood. With that in mind, we have included chapters on the basic technology of such units, e.g., high-voltage stalk design, grid design and geometry, and other non-spherical geometries. Thus this book should be useful for developing IEC experiments in university laboratories for students as well as researchers. It is the hope of the authors that this book aid the growth of IEC fusion research aimed at near-term spin-off applications and ultimately a stand-alone fusion power plant. Features of This Book Chapter 1 discusses the background and basics of IEC fusion, as well as some experiments. IEC fusion offers many potential advantages, including simplified support structures and the ability to create non-maxwellian plasmas that can be used with a variety of fusion fuels. The basic IEC approach is to create a potential well through electrostatic confinement of one of the plasma species in a dynamic (inertial) configuration. Inertial effects associated with dynamic motion of the confined species are essential to avoid plasma losses. Chapter 2 discusses the theory of potential well traps in the IEC. It might seem that the two injection methods are similar. However, important differences occur due to the mass difference in the particles that are then effectively providing the inertia to electrostatically confine the other species. This difference is discussed through the analyses presented in this chapter. This chapter focuses on potential

7 Preface vii well formation and fully ionized spherical IECs. Other geometries have also been studied to see whether such wells could be formed. One example is a gridded cylindrical device that can be viewed as a two-dimensional version of the spherical IEC. However, a spherical geometry has generally been favored due to the three dimensional convergence of the ion beam in the central core. Chapter 3 discusses gas discharges in gridded IECs. Many experimental IEC devices employ a gas discharge between the grid and vacuum vessel wall (or outer grounded grid) as an ion source. In this chapter we examine some of the basic physics of such discharges and the resulting voltage current characteristics in the IEC. Chapter 4 discusses high-voltage stalk design for IECs. Stalk design is crucial for successful internal source IEC device operation. This is particularly true for applications where very high voltages are desired. The requirements for an ideal stalk design are listed. Chapter 5 discusses IEC grid materials and construction. This chapter concentrates on grids for spherical IEC systems. The construction of the IEC grid is complex in that a number of factors contribute to grid performance relative to key issues such as neutron production and ion confinement times. In this chapter we discuss issues that affect the selection of the grid materials and methods for assembling a grid. Chapter 6 covers effects of grid design and geometry in more detail. Grid geometry plays an important role in the performance of a gridded spherical IEC device because the ion recirculation, hence the reaction rate, is strongly affected by the orientation and size of openings in the cathode in grid design. Several aspects of the effect of grid design on IEC operational performance are discussed. Chapter 7 discusses studies of space charge limited flow analysis. The classical analyses presented in this chapter are of interest for several reasons. First, these analyses are historic in providing initial insight into space charge effects in diodes carrying large currents. Second, they illustrate techniques originally employed to solve the equations involved. Third, to some extent, the limiting current prediction as a function of applied voltage and anode cathode spacing roughly apply to the IEC behavior prior to the point where, with combined ion electron currents, virtual electrodes are formed. The application of space charge limited flow concepts to an actual IEC experiment is discussed. In that case, issues of plasma flow convergence and the high density converged core become important aspects of the problem. Chapter 8 discusses ion and electron current scaling issues related to how the fusion rate scales with the ion current in the ion-injected type IEC. Chapter 9 discusses cylindrical and other IEC geometries. Spherical geometry has been widely used following Farnsworth s original studies that stressed the possibility of three-dimensional compression of recirculating beams in the central core of this geometry. This becomes a very important feature if the goal is net power production. However, in many other applications, less compression (e.g. two-dimensional compression in a cylindrical geometry) may be adequate. Indeed, a unique feature of the IEC is that we can adapt its geometry to a number of important near-term applications short of power production. In this chapter we

8 viii Preface consider cylindrical, Jet extraction, dipole-assisted, and magnetically-coupled IEC geometries. These provide unique capabilities for various near-term commercial applications. Chapter 10 discusses other IEC concepts and experiments. Here we have chosen a few experiments that have received attention and supplement discussions in Chaps. 1, 2, and 9, in order to explain some issues and status relative to gridded devices for near-term applications such as neutron sources and also to address some issues such as ion injection related to future fusion power units. Chapter 11 discusses IEC diagnostics. A wide variety of plasma diagnostics can be applied to an IEC. However, the specific diagnostics incorporated are usually selected based on the objective of the research or application involved. The most common of diagnostics used in IEC research are discussed in this chapter. Emphasis is placed on how these diagnostics are modified for use in the IEC and on the interpretation of the measurements made. Chapter 12 discusses potential applications. The ability to use the IEC for practical applications with operation well below energy breakeven is a unique attractive feature of this device. In this chapter we discuss some NAA applications, along with medical isotope production. With some increase in energy gain and power, an IEC neutron driven subcritical fission assembly for student labs seems feasible. We discuss that use in this chapter, along with more demanding use in future fusion fission hybrid reactors. IEC fusion space propulsion, another future application, is discussed to stress the potential for high power-to-weight systems using the IEC. Chapter 13 discusses reactor confinement theory and visions for an IEC power reactor. Various semi-analytic and computer simulations of plasma confinement in the potential traps created by various IEC devices are discussed, and key issues such as ion thermalization times, energy balances, and instabilities caused by deviations from equilibrium conditions are addressed. Urbana, IL, USA Erode District, TN, India George H. Miley S. Krupakar Murali

9 Acknowledgments I (George Miley) started writing this book with an IEC fusion reactor in mind. However, when S. K. Murali joined the project, he pointed out the importance of covering the technology of gridded devices in order to push immediate applications and student experiments ahead. He added much of this very important information to the book, making the presentation much more useful to the community. I would like to thank my wife, Liz, my family, and my former students and colleagues who assisted me during my IEC fusion research. I am grateful to all of them for their support. Also, both authors are very grateful to Robyn Bachar for the extensive work she has done on this book. Her efforts included searching out many reference papers, proofing and editing text, formatting materials, and offering many constructive suggestions. Her work was essential for completion of this book. We would also like to thank our editor at Springer, Merry Stuber, for her hard work and her patience with this book. I (S. Krupakar Murali) would like to first thank Dr. Miley for giving me the opportunity to work alongside him in preparation of this book. I would also like to once again thank Prof. Gerald Kulcinski, my thesis advisor, for having introduced me to this field in Prof. Kulcinski and Prof. John Santarius from the University of Wisconsin, Madison, have both been instrumental in shaping my understanding of IEC devices. They gave me a free hand in exploring my ideas while I was still a graduate student, and the encouragement they showered on me even when some of my experiments failed played a crucial role in the knowledge I had gathered in the field, and that ultimately led me to join Prof. Miley in preparing this book. I would also like to thank my wife, Kasthuri, and our two children (Vaibhav, our son, and Gowri, our daughter) who helped push me to extremes to achieve my goals. My parents have always played a major role in shaping my life, and they have never stopped supporting, encouraging, and blessing me. My parents-in-law have extended much help while preparing this book, and kept me going even at times when things were difficult to handle, and they supported me in every way possible. I owe them a debt of gratitude for this. I would also like to thank my sister- and brother-in-law who have always encouraged me. ix

10 x Acknowledgments Prof. Miley and I would finally like to thank all our fellow researchers who have contributed to the progress of IEC technology. This book would not be possible without their hard work and dedication to the field. We strongly encourage them to continue their excellent work to help IEC technology achieve new heights. We sincerely hope that this book will help the academic community in familiarizing students to various forms of radiation, their generation techniques using IEC reactors, and the related applications.

11 Contents 1 Background, Basics, and Some IEC Experiments Introduction Comments About Current Studies Gridded IEC Devices IEC Fusion Reactor Issues IEC History Prior Virtual Electrode Studies Recent IEC Studies Some IEC Basics Thorson s Triple Grid IEC Device Murali s Triple Grid RF-Based IEC Device The Ring-Shaped Magnetron Ion Source (RS-MIS)-Based IEC Device Miley s Ion-Injected Device Nebel Barnes POPS Device Murali s High-Pressure IEC Concept Bussard HEPS (or Polywell) Concept Barnes Nebel Penning Trap Summary References Theory of Well Potential Traps in the IEC Introduction Ion Velocity Distribution Conditions for Maximum Thermonuclear Power The Farnsworth Fusor Farnsworth s Modulation Concept The Polywell: A Spherically Convergent Ion Focus Concept Summary References xi

12 xii Contents 3 Gas Discharges in Gridded IECs Introduction Types of Gas Discharges Direct Current Glow Discharge Mechanism DC Discharges in Linear Two Electrode Geometries at Low Pressure Discharge Characteristics in the IEC Discharges in the Spherical Geometry Used in an IEC Device Spherical Geometry Studies Breakdown Voltage Characteristics Voltage Versus (pd) Measurements in an IEC Scaling Laws Cylindrical IECs Summary References High-Voltage Stalk Design for IECs Introduction Various Stalk Designs and Design Considerations Institute of Advanced Energy, Kyoto University, Japan Design Idaho National Environmental Laboratory (INEL) Design University of Illinois at Urbana Champaign (UIUC) Designs University of Wisconsin (UW), Madison Designs A Stalk Design Using Lessons Learned from Prior Ones Various Types of Damage Caused to High-Voltage Stalks Surface Breakdown Flashover Across Solid Insulators Prebreakdown Conduction Mechanism Characteristics of Gap Prebreakdown Currents Review of Breakdown Basics High-Voltage Bushing Design Use of Bushing for Stalk Design Non-condenser Bushing Condenser Bushings Stress Control in Stalks Dielectric Materials Mixed Dielectrics Polarization E-Field Profiles Coaxial Cylindrical Fields

13 Contents xiii 4.8 Computation of the Optimum Radius Ratio for Cylindrical Geometry Spherical Electric Fields Mechanical Stress Due to Electrostatic Charge Multistage Stalk Design Hollow Stalk Design Nonconductive Isolated Stalk Design Summary References IEC Grid Materials and Construction Introduction Grid Material Selection Effect of Thermionic Electrons on the Performance oftheiecdevice Chordwire Diagnostic for Electron Current Studies Studies of Thermionic Emission Effects on the Neutron Production Rate Study of Effects of Asymmetric Heating of the Cathode Grid Treatment of Uneven Temperature in Emission Equations Grid Wire Material Selection Construction of Grids Rapid Prototyping for Grid Construction Using Carbon Nanotubes to Construct Grids Multi-grid Design and Fabrication Summary References Effect of Grid Geometry on IEC Performance Introduction Transformation of Line Source into a Volume Source Proton/Neutron (P/N) Ratio Fusion Regimes Inside an IEC Device Grid Rotation Experiments for Potential Well Studies Grid Rotation Experimental Setup Calculation of Fusion Rate Using a Single Loop Grid Extension of Study to Entire Grid and Microchannel Effects Detector Calibration Factors for Various Source Regimes Calibration Factor for a Converged Core Created by Microchannel Intersection Calibration Factor for Embedded Source

14 xiv Contents Calibration Factor for a Volume Source Dominated by Microchannels Total Calibration Factor Grid Geometry for Jet Mode Operation Characteristics of the Jet Mode Regime Jet Mode Discharge Characteristics Size Scaling for IEC Jet Mode Development of a Compact IEC Device Summary References Space Charge-Limited Flow Introduction Space Charge-Limited Flow in a Parallel Plate Vacuum Diode Child Langmuir Law for Space Charge-Limited Emission Geometry of a Parallel Infinite Plate Vacuum Diode Derivation of the Child Langmuir Law Limitations of the Child Langmuir Derivation Langmuir Spherical Geometry Problem Langmuir s Numerical Solution Effect of Grid Radius Analytical Solution of Space Charge-Limited Current Cylindrical System Spherical System Experimental Observations of Space Charge-Limited Flow in Current IECs Experimental Observations of Some Effects of Space Charge-Limited Flow Converged Core Condition with Space Charge-Limited Flow Flow Convergence Measurement Core Density Measurements Summary References Ion and Electron Current Scaling Issues Introduction Reaction Regime Issues Multi-grid IEC Concept Low-Pressure Experiments Studies of Energy Loss Mechanisms Secondary Electron Emission Molecular Effects on the Secondary Electron Emission

15 Contents xv 8.3 Impurity Effects on SEE Photoemission Electrons Field Emission Tests of Grid Materials Summary References Cylindrical and Other IEC Geometries Introduction Cylindrical IECs Electrically Driven IEC Jet Thruster The Dipole-Assisted IEC (DaIEC) DaIEC Experiments Microchannel Type IEC Thruster A Counter-Streaming Beam Linear IEC Multiple Ambipolar Recirculating Beam Line Experiment (MARBLE) Ion Confinement in MARBLE Potential Applications for MARBLE Shaban s Magnetic-Assisted IEC Summary References Various Other IEC Concepts and Experiments Introduction Hirsch Ion Gun Injected Experiment SIGFE Six-Gun Experiment at University of Wisconsin Star Mode with Vane-Type Grids and with Pulsed Operation Pulsed Operation Getter Pumping of an IEC Device Compact IEC Neutron Source for Landmine Detection at Kyoto University Helicon-Injected IEC for 3 He Experiments at University of Wisconsin University of Wisconsin Helicon Source The University of Illinois Helicon-IEC Thruster, HIIPER Numerical Simulations for HIIPER Electron-Injected IEC Concepts Experimental Observation of POPS Oscillations Particle Simulation of POPS Plasma Compression Penning Trap Concept Summary References

16 xvi Contents 11 IEC Diagnostics Introduction Neutron Detectors Polyethylene-Moderated 3 He Gas Filled Neutron Detectors BF 3 Neutron Detectors Typical Detector Electronic Arrangement Operational Regions Comparison of Gas Filled Detectors Example of a 3 He Detector in an IEC Experiment Calibration of Neutron Detectors Comments About Nonlinearity in Detection Rates Bubble Detectors Silver Activation Detectors Solid-State Detectors Energy Required for the Creation of Electron Hole Pair Energy Calibration of the Proton Spectrum Understanding the Proton Energy Spectrum Recorded with Si Detectors Comments About D 3 He Fueled IEC Reactions Noise Levels in Silicon Detectors Natural Diamond Detectors Electron Noise Calculation of the Proton Deflection Inside the Detector Port Fusion Ion Doppler (FIDO) Diagnostic Scintillation Detectors Negative Ions in Gridded IEC Devices Magnetic Deflection-Energy Analyzer Laser-Induced Fluorescence of Well Profiles Spectroscopic/Langmuir Probe Measurements of Ion Energies Langmuir Probe Measurements Ion Energy Measurements Diagnostics for an IEC Plasma Jet Gridded Energy Analyzer Faraday Cup Diagnostics Plasma Force Sensor Summary References

17 Contents xvii 12 Potential Applications Introduction Neutron/Proton/X-ray Sources Production of Medical Isotopes Chemical Explosives Detection Using aniecdevice Detection of Highly Enriched Uranium (HEU) Integrated Interrogation System Design of a Total Integrated Interrogation System for Luggage Inspection Integrated System Detection Methods Pulsed Power Supply for a Pulsed IEC Neutron Source Detector Array for the Integrated System Fuzzy Logic Analysis System Adaptation to Container Ships IEC Fusion Space Propulsion Design Studies Magnetically Channeled Spherical IEC Array (MCSA) Concept Recirculation of Radial Belt Cone Losses Retrapping of Axial-Loss Particles IEC Electrically Driven Space Thruster, HIIPER Comments About Scale-Up to p B 11 IEC Space Power Unit/Thruster IEC-Driven Fusion Fission Hybrids Possible Initial Use in Low-Power Research Reactors IEC Configuration for the Subcritical Reactor Design Summary References Reactor Confinement Theory and IEC Reactor Visions Introduction Early Ion Thermalization and Energy Balance Studies of Potential Well-Trapped Plasma Bounce-Averaged Fokker Planck (BAFP) Analysis Comparison of Semi-analytic and BAFP Code Results Angular Momentum Effects on a Potential Well Potential Well Structure Deep Well Studies Early Theoretical Studies of Potential Well Traps Analytical Study of the Virtual Electrode Structure Experimental Potential Well Studies

18 xviii Contents 13.5 Stability Analysis of Non-Maxwellian Trapped Plasma Particle-In-Cell (PIC) Code Stability Analysis Energy Balance Study Beam Background IEC Fusion Rate Simulations Comments About IEC Reactor Development IEC Aneutronic Fusion Ion Injection with Controlled Angular Momentum The Polywell Approach Multi-Grid IEC Lens-Focused IEC POPS and the Penning Trap IEC Vision of a Future p B 11 Fusion Plant Summary References Index