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The Electrostatic AcceleratorA versatile tool

The Electrostatic AcceleratorA versatile tool

Ragnar HellborgUniversity of Lund, Lund, Sweden

Harry J WhitlowUniversity of Louisiana at Lafayette, Lafayette, USA

Morgan & Claypool Publishers

Copyright ª 2019 Morgan & Claypool Publishers

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ISBN 978-1-64327-356-3 (ebook)ISBN 978-1-64327-353-2 (print)ISBN 978-1-64327-354-9 (mobi)

DOI 10.1088/2053-2571/aaea76

Version: 20190301

IOP Concise PhysicsISSN 2053-2571 (online)ISSN 2054-7307 (print)

A Morgan & Claypool publication as part of IOP Concise PhysicsPublished by Morgan & Claypool Publishers, 1210 Fifth Avenue, Suite 250, San Rafael, CA,94901, USA

IOP Publishing, Temple Circus, Temple Way, Bristol BS1 6HG, UK

To our families.

Contents

Preface xii

Acknowledgements xiii

Author biographies xiv

1 Introduction 1-1

References 1-3

2 The field of accelerator techniques 2-1

2.1 Different types of accelerator 2-1

2.2 Orbital accelerators 2-1

2.2.1 Cyclotrons 2-1

2.2.2 Synchrocyclotrons and isochronous cyclotrons 2-2

2.2.3 Synchrotrons 2-2

2.3 Linear accelerators 2-2

2.4 Direct voltage accelerators 2-2

2.5 Tandem electrostatic accelerator 2-5

References 2-6

3 History of electrostatic accelerators 3-1

3.1 Development of Van de Graaff accelerators 3-1

3.2 The Herb accelerators 3-2

3.3 Commercially produced accelerators 3-3

3.4 The development of tandem accelerators 3-4

3.5 The big machines 3-6

References 3-7

4 Electrostatics 4-1

4.1 Field distributions 4-2

4.2 Potential dividers 4-4

References 4-4

5 Insulating gases 5-1

References 5-3

vii

6 Charging systems 6-1

6.1 Belt charging systems 6-1

6.2 Chain charging systems 6-3

6.3 Cascade generator charging systems 6-4

References 6-5

7 Voltage distribution systems 7-1

7.1 Corona point systems 7-2

7.2 Resistor chains 7-2

Reference 7-2

8 High voltage stabilisation 8-1

8.1 Feedback voltage stabilisation 8-2

8.1.1 Voltage multiplier-high voltage supplies 8-2

8.1.2 Stabilisation of chain- and belt-charged accelerators 8-3

References 8-5

9 Accelerator tubes 9-1

9.1 Beam optics 9-1

Reference 9-4

10 Ion stripper system and terminal pumping 10-1

10.1 Charge exchange 10-1

10.1.1 Foil strippers 10-1

10.1.2 Gas strippers 10-2

10.1.3 Terminal pumping 10-3

References 10-4

11 Electron sources 11-1

11.0.1 Thermionic emission 11-1

11.0.2 Thermionic emission of electrons from a surface 11-1

11.0.3 Field emitters 11-2

11.0.4 Plasma electron sources 11-2

11.0.5 Photoelectric electron emission 11-3

11.1 Thermionic electron gun 11-3

References 11-14

The Electrostatic Accelerator

viii

12 Positive ion sources 12-1

12.1 RF-ion sources 12-1

12.2 Penning ion sources 12-2

12.3 Duoplasmatron ion sources 12-3

Reference 12-4

13 Negative ion formation processes and sources 13-1

13.1 Negative ion formation 13-1

13.1.1 Direct extraction from gaseous plasma 13-1

13.1.2 Negative-ion formation through charge exchange 13-1

13.1.3 Sputter-ion sources as a source of negative ions 13-2

Reference 13-5

14 Equipment for beam diagnostics 14-1

14.1 Measurement of the beam current 14-1

14.2 Monitoring the beam diameter and position 14-2

14.3 Beam profile monitors 14-2

14.4 Beam stoppers and safety equipment 14-2

Reference 14-3

15 Charged particle optics and beam transport 15-1

15.1 Specification of the ion beam 15-1

15.1.1 Beam currents, fluxes and fluence 15-1

15.2 Charge particle beam optics and beam transport characteristics fordifferent types of end-station beam-lines

15-3

15.3 Accelerator ion optics 15-3

15.3.1 Particle acceleration and the Lorentz equation 15-3

15.3.2 The drift section 15-6

15.3.3 Electrostatic acceleration 15-6

15.3.4 Electrostatic deflection 15-8

15.3.5 Magnetic dipole 15-9

15.3.6 Magnetic quadrupoles 15-11

References 15-13

16 Radiation protection at an accelerator laboratory 16-1

16.1 Types of radiation 16-1

The Electrostatic Accelerator

ix

16.1.1 Interactions of accelerator-induced radiation with matter 16-3

16.2 Radiation dosimetry 16-5

16.3 Detecting ionising radiation 16-6

Reference 16-7

17 Computer control of accelerators 17-1

17.1 Introduction 17-1

17.2 Distributed intelligence 17-2

17.2.1 GUI design 17-4

17.2.2 Interlock design 17-4

17.3 Smart accelerators and Industrie 4.0 17-5

17.4 Obsolescence considerations 17-5

17.4.1 Control system security 17-6

References 17-6

18 Vacuum technology for electrostatic accelerators 18-1

18.1 Introduction 18-1

18.2 Basic high vacuum technology 18-2

18.3 Kinetic theory and gas flow in vacuum systems 18-2

18.3.1 Differential pumping 18-5

18.4 Vacuum components 18-6

18.4.1 Vacuum pumps 18-6

18.4.2 Roughing and backing pumps 18-8

18.4.3 Vacuum valves 18-9

18.4.4 Vacuum meters 18-10

18.5 Vacuum fittings and materials 18-10

18.5.1 Vacuum fittings 18-10

18.5.2 Materials 18-11

18.6 Accelerator vacuum systems 18-11

18.6.1 Troubleshooting accelerator vacuum systems 18-13

References 18-13

19 Environmental and safety aspects of electrostatic accelerators 19-1

19.1 Introduction 19-1

19.2 Building environmental aspects 19-1

19.2.1 Electrical supply 19-1

19.2.2 Ventilation 19-3

The Electrostatic Accelerator

x

19.2.3 Sulphur hexafluoride (SF6) 19-3

19.2.4 Other services 19-5

19.3 Environmental effects on electrostatic accelerators 19-6

19.3.1 Ground vibrations 19-6

19.3.2 Earthquakes 19-6

19.3.3 Magnetic fields 19-7

19.3.4 Flooding 19-8

19.3.5 Radiation shielding of the accelerator laboratory 19-8

19.3.6 Chemical environment 19-8

References 19-9

20 Applications of electrostatic accelerators 20-1

20.1 Introduction 20-1

20.2 Atomic and nuclear reactions 20-1

20.3 Charged particle beam modification of materials 20-3

20.3.1 Basic interactions 20-3

20.3.2 Electron irradiation 20-4

20.3.3 Ion beam modification of materials 20-6

20.4 Ion beam analysis methods 20-9

20.4.1 MeV ion microprobes 20-10

20.4.2 Ion beam analytical methods 20-10

20.5 Accelerator mass spectrometry (AMS) 20-16

20.5.1 Ion sources 20-16

20.5.2 Detectors 20-17

20.5.3 Gas ionisation detectors 20-17

20.5.4 Semiconductor detectors 20-17

20.5.5 Time-of-flight detectors 20-18

20.5.6 Gas-filled magnets 20-18

20.5.7 x-ray detectors 20-19

References 20-19

Appendix SI units and other units A-1

The Electrostatic Accelerator

xi

Preface

Electrostatic accelerators have been at the forefront of modern technology since thedevelopment by Sir John Cockroft and Ernest Walton in 1932 of the first acceleratorwhich was the first to achieve nuclear transmutation. This endeavour earned themthe Nobel Prize in Physics in 1951. The early development of these accelerators isepitomised in the semi-fictional tribute The Fly in the Cathedral by Brian Cathcart[1]. The applications of Cockroft and Walton’s development have been far reaching,even into our kitchens where it is employed to generate the high voltage needed forthe magnetron in microwave ovens. Other electrostatic accelerator related Nobelprize winning developments that have had a major socio-economic impact are: theelectron microscope where the beams of electrons are produced by an electrostaticaccelerator; x-rays and computer tomography (CT) scanners where the x-rays areproduced using an electron accelerator; and microelectronic technology where ionimplantation is used to dope the semiconductor chips which form the basis of ourcomputers, mobile phones and entertainment systems. Although the electrostaticaccelerator field is over 90 years old, and only a handful of accelerators are used fortheir original purpose in nuclear physics, the field and the number of accelerators isgrowing more rapidly than ever. This is driven by spearheading applicationsincluding accelerator mass spectrometry, which was developed by Grove toimprove over the radioactive decay measurement for 14C dating and is used forpharmacokinetics research by major drug companies. Other applications arefabrication of qubits that are transforming quantum computing from fundamentaltheoretical predictions to reality, studying disease processes using micro-PIXE andqualifying electronic devices for use on space missions where the charged particleradiation fluxes may cause malfunctions, as well as many other applications.

The objective of this book is to collect together the basic science and technologythat underlies the electrostatic accelerator field so it can serve as a handbook,reference guide and textbook for accelerator engineers as well as students andresearchers who work with electrostatic accelerators.

References[1] Cathcart B 2005 The Fly in the Cathedral (New York: Farrar, Straus and Giroux)

xii

Acknowledgements

Two persons have kindly produced and provided high quality figures to this book.Max Strandberg has produced figures 2.2, 2.4 and 6.1; and Kjell Håkansson, formerchief engineer at the Pelletron laboratory in Lund, has produced figures 19.3, 6.2 and10.1.

Over the years, we have both worked closely with many excellent AcceleratorScientists, Engineers and Technicians. From these people we have learnt a greatdeal. We warmly thank M Edouard Guibert, Mr Armin DeVera, Hr KjellHåkansson, Hr Christer Nilsson, Hr. Vagn Toft, Dr David Hole, Mr BarryFarmery, Dr Armas Fontell, Hr Jonas Åström, Professor Göran Possnert,Professor Timo Sajavaaraa, Professor Juhani Keinonen, Professor KlasMalmqvist, Professor Sir Michael Thompson, and the late Professor Hans HenrikAndersen, the late Professor Sven AE Johansson, the late Mr Norman Priestley andthe late Hr Gösta Widmark. We are also grateful to the representatives of theaccelerator manufacturers Mr Gregg Norton (NEC) and Henri van Oosterhout(HVEE) for their help and support through the years.

xiii

Author biographies

Ragnar Hellborg

Ragnar Hellborg is emeritus Full professor of Applied Physics at theDepartment of Physics, University of Lund in Sweden. He hasworked in the field of applied physics using electrostatic acceleratorsfor more than 50 years.

Harry J Whitlow

Harry J Whitlow is Full professor of Physics and Director of theLouisiana Accelerator Center at the University of Louisiana atLafayette, USA. He has a long career in applying MeV ionaccelerator-based methods to a wide range of fundamental andapplied problems.

xiv