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Development of Instrumentation for Low Energy Beams Development of Instrumentation for Low Energy Beams Thesis submitted in accordance with the requirements of the University of Liverpool for the degree of Doctor in Philosophy by Janusz Harasimowicz February 2013 b Abstract Ion and antiproton beams at keV energies are very attractive for a number of funda- mental studies. The diagnostic of these beams, however, is a challenge because most detectors are either not sensitive enough or too disturbing. In this work, a set of optimised detectors has been developed to suit the particular beam diagnostic needs of the novel Ultra-low-energy Storage Ring (USR) at the future Facility for Low-energy Antiproton and Ion Research (FLAIR), accommodating as few as 107 particles at energies down to 20 keV. The instrumentation includes beam profile monitors based on scintillating screens and secondary electron emission, ultra-sensitive Faraday cups for absolute intensity measurements, and capacitive pick-ups for on-line beam position monitoring. This thesis presents results from theoretical studies and modelling, the design of prototypes of all monitors, and results from measurements with beam. All detectors are characterised in detail, their individual limitations are described and options for further improvements are indicated. Whilst initially developed for the USR, the instrumentation described in this thesis is also well suited for use in other low-intensity, low-energy accelerators, storage rings, and beam lines. i 0. ABSTRACT ii Contents Abstract i Contents iii Acronyms ix Acknowledgements xiii 1 Introduction 1 1.1 Background . 1 1.2 Antiproton Machines . 2 1.2.1 Production of Antiprotons . 2 1.2.2 Antiproton Accumulator (AA) and CERN p¯pCollider . 2 1.2.3 Low Energy Antiproton Ring (LEAR) . 3 1.2.4 Antiproton Decelerator (AD) . 3 1.2.5 Extra Low Energy Antiproton Ring (ELENA) . 4 1.2.6 Facility for Low Energy Antiproton and Ion Research (FLAIR) . 5 1.2.7 Ultra Low Energy Storage Ring (USR) . 6 1.3 Project Goals . 8 2 Low-Energy Beam Diagnostics 9 2.1 Introduction . 9 2.2 Beam Profile Measurements . 10 2.2.1 Beam Scrapers . 10 2.2.2 Gaseous Ionization Detectors . 11 2.2.3 Scintillating Screens . 13 2.2.4 Secondary Emission Monitors . 15 2.2.5 Semiconductor Detectors . 19 iii CONTENTS 2.3 Beam Position Measurements . 20 2.4 Beam Intensity Measurements . 22 2.4.1 Beam Current Transformers . 22 2.4.2 Capacitive Pick-ups . 23 2.4.3 Faraday Cups . 24 2.4.4 Particle Counters . 25 2.4.5 Annihilation Monitors . 25 2.5 Summary . 26 3 Scintillating Screens 29 3.1 Motivation . 29 3.2 Theoretical Background . 30 3.2.1 Scintillation Mechanisms . 30 3.2.2 Considerations for Protons . 31 3.2.3 Considerations for Antiprotons . 32 3.3 Experimental Setup . 33 3.3.1 Beam Line . 33 3.3.2 Test Setup . 34 3.3.3 Scintillating Screens . 35 3.3.4 Image Recording . 36 3.4 Results with Protons . 37 3.4.1 Beam Profiles . 37 3.4.2 Resolution . 38 3.4.3 Beam Current . 40 3.4.4 Detection limits . 46 3.5 Perspectives . 47 3.6 Summary . 49 4 Capacitive Pick-Up 51 4.1 Motivation . 51 4.2 Theory of Capacitive Pick-Ups . 52 4.2.1 General Formalism . 52 4.2.2 Principle of Position Measurement . 53 4.2.3 Response of a Diagonally Cut Pick-Up . 54 4.2.4 Low-Velocity Beams . 56 iv CONTENTS 4.3 Design Considerations . 59 4.3.1 Pick-Up Signals Estimation . 59 4.3.2 Corrections for Low-Velocity Beams . 62 4.3.3 Noise Estimation . 63 4.3.4 Effect of Noise on the Beam Position Determination . 66 4.3.5 Mechanical Tolerances and Misalignment . 66 4.3.6 Signal Digitisation . 68 4.4 Technical Design and Construction . 76 4.4.1 Mechanical Design . 76 4.4.2 Electronics and Signal Processing . 78 4.5 Experimental Tests with a Current-Carrying Wire . 83 4.5.1 Experimental Setup . 83 4.5.2 Results with the Current-Carrying Wire . 84 4.6 Simulations of Particle Beams . 87 4.7 Summary and Perspectives . 92 5 Faraday cup 95 5.1 Motivation . 95 5.2 Design Considerations . 96 5.2.1 Principle of Operation . 96 5.2.2 Range of Projectiles in Matter . 97 5.2.3 Backscattered Particles . 99 5.2.4 Secondary Particles . 106 5.2.5 Heat Load . 108 5.2.6 Signal Amplification . 109 5.2.7 Noise . 111 5.3 Design and Construction . 114 5.3.1 Conceptual Design and Performance Analysis . 114 5.3.2 Mechanical Design . 121 5.3.3 Electrical Design . 122 5.4 Experiments with Electrons . 125 5.4.1 Experimental Setup . 125 5.4.2 Results with Electrons . 127 5.5 Experiments with Protons . 130 5.5.1 Experimental Setup . 130 v CONTENTS 5.5.2 Results with Protons . 132 5.6 Summary and Perspectives . 138 6 Secondary Emission Monitor 141 6.1 Motivation . 141 6.2 Principle of Operation . 142 6.2.1 Secondary Emission Monitor Working Principle . 142 6.2.2 Secondary Electron Emission and Guidance . 142 6.2.3 Secondary Electron Detection . 143 6.3 Design Considerations . 144 6.3.1 Considerations for Primary keV Beams . 144 6.3.2 Considerations for Secondary Particles . 147 6.3.3 Technical Considerations . 157 6.4 Prototype Design and Construction . 160 6.4.1 Mechanical Design . 160 6.4.2 Detector Components . 161 6.4.3 Electrical Design . 163 6.5 Experiments with Electrons . 164 6.5.1 Experimental Setup . 164 6.5.2 Experimental Results . 166 6.6 Experiments with Protons . 169 6.6.1 Experimental Setup . 169 6.6.2 Experimental Results . 171 6.7 Experiments with Antiprotons . 176 6.7.1 Antihydrogen Experiment AEGIS . 176 6.7.2 Secondary Emission Monitor Setup at AEGIS . 178 6.8 Summary . 184 7 Conclusions 189 7.1 Summary . 189 7.2 Future Developments . 191 A Secondary Electron Emission Model 193 Bibliography 195 List of Figures 219 vi CONTENTS List of Tables 227 vii CONTENTS viii Acronyms AA Antiproton Accumulator AC Antiproton Collector AD Antiproton Decelerator ADC analogue-to-digital converter AEGIS Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy ALPHA Antihydrogen Laser PHysics Apparatus ASACUSA Atomic Spectroscopy And Collisions Using Slow Antiprotons ATRAP Antihydrogen TRAP BCT beam current transformer CAD computer-aided design CCC cryogenic current comparator CCD charge-coupled device CERN Conseil Europ´eenpour la Recherche Nucl´eaire CR Collector Ring CSDA continuous slowing-down approximation CSR Cryogenic Storage Ring CVD chemical vapour deposition DESIREE Double ElectroStatic Ion Ring ExpEriment DFT discrete Fourier transform DLA delay line anode ELENA Extra-Low-ENergy Antiproton ring ELISA ELectrostatic Ion Storage ring, Aarhus EXCYT EXotics at the CYclotron and Tandem FAIR Facility for Antiproton and Ion Research ix Acronyms Fermilab Fermi National Accelerator Laboratory FLAIR Facility for Low-Energy Antiproton and Ion Research FLSR Frankfurt Low-energy Storage Ring FRIBS in-Flight Radioactive Ion BeamS FWHM full width at half maximum GANIL Grand Acc´el´erateurNational d'Ions Lourds GEM gas electron multiplier GSI Gesellschaft f¨urSchwerionenforschung GUI graphical user interface HITRAP Heavy Ion TRAP HPD hybrid photo diode HV high voltage ICT integrating current transformer INFN-LNS Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud IPM ionization profile monitor ISOLDE ISOtope separator on-Line DEtector KEK K¯oEnerug¯ıKas¯okiKenky¯uKik¯o LEAR Low-Energy Antiproton Ring LEIR Low-Energy Ion Ring LHC Large Hadron Collider LSR Low-energy Storage Ring MCP microchannel plate MPI-K Max-Planck-Institut f¨urKernphysik MSL Manne Siegbahn Laboratory.
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