Dr Dan Faircloth BEng(Hons) MSc PhD MInstP MIET CEng
Senior Research Engineer
Low Energy Beams Group Leader
ISIS, Rutherford Appleton Laboratory, Oxfordshire, UK
[email protected]
For most recent work see:
Comprehensive list of pre 2017 work:
101. Demonstrating H- Beam Focusing Using An Elliptical Einzel Lens
Proceedings of NIBS2016, Oxford. TueO5. AIP Conference Proceedings 2017.
H- ion source research is being performed at the ISIS spallation neutron and muon facility on a dedicated Vessel for Extraction and Source Plasma Analyses (VESPA). The ion extraction and optics system presently being used on ISIS is centered on a combined-function sector dipole magnet. This traps cesium vapor escaping the ion source; mass-separates co-extracted electrons and stripped neutrals, and weak-focusses the highly asymmetric slit-shaped ion beam. Unfortunately the added drift length through the magnet under strong space-charge forces means up to 50% of the beam is collimated on the magnet. The VESPA has shown that the ISIS ion source actually produces 80 mA of beam current at standard settings, but because of magnet collimation only 55 mA is injected into the solenoid Low Energy Beam Transport (LEBT). A new purely electrostatic post-extraction system incorporating an einzel lens with an elliptical aperture is currently under test. This allows much greater flexibility of perveance and phase space matching for injection into the LEBT and Radio Frequency Quadrupole (RFQ). This paper discusses high voltage breakdown mitigation strategies and presents the first results of the novel elliptical transport system. So far, 70 mA of beam has been transported through the new system with a normalized transverse RMS emittance of 0.2 π mm mrad.
100. Initial Commissioning Of The Rutherford Appleton Laboratory (RAL) Scaled Negative Penning Ion Source
Proceedings of IPAC2016, Busan, Korea, TUPMR032
A new high duty factor, scaled Penning surface plasma source is being developed at RAL. This paper provides initial commissioning results. A stable high-current (up to 100 A) pulsed discharge is obtained, but the anode overheats, caused by poor thermal contact at elevated temperatures. The overheating anode yields a noisy discharge, with low output current, and makes high duty factor operation impossible. The performance of a thermal interface material for aperture plate (plasma electrode) cooling is detailed. An update on the cathode heaters is provided. The anode to source-body fit is analysed at different temperatures for different combinations of mechanical tolerances. This offers insights when compared to ISIS operational sources. A new anode with modified tolerance dimensions for improved fit is being manufactured and will be tested in June 2016.
Review of Scientific Instruments 87, 02B139 (2016); http://doi.org/10.1063/1.4936120
CERN's 160 MeV H− linear accelerator (Linac4) is a key constituent of the injector chain upgrade of the Large Hadron Collider that is being installed and commissioned. A cesiated surface ion source prototype is being tested and has delivered a beam intensity of 45 mA within an emittance of 0.3 π ⋅ mm ⋅ mrad. The optimum ratio of the co-extracted electron- to ion-current is below 1 and the best production efficiency, defined as the ratio of the beam current to the 2 MHz RF-power transmitted to the plasma, reached 1.1 mA/kW. The H− source prototype and the first tests of the new ion source optics, electron-dump, and front end developed to minimize the beam emittance are presented. A temperature regulated magnetron H− source developed by the Brookhaven National Laboratory was built at CERN. The first tests of the magnetron operated at 0.8 Hz repetition rate are described.
Review of Scientific Instruments 87, 02B122 (2016); http://doi.org/10.1063/1.4934580
A vessel for extraction and source plasma analyses (VESPA) is operational at the Rutherford Appleton Laboratory (RAL). This project supports and guides the overall ion source R&D effort for the ISIS spallation neutron and muon facility at RAL. The VESPA produces 100 mA of pulsed H− beam, but perveance scans indicate that the source is production-limited at extraction voltages above 12 kV unless the arc current is increased. A high resolution optical monochromator is used to measure plasma properties using argon as a diagnostic gas. The atomic hydrogen temperature increases linearly with arc current, up to 2.8 eV for 50 A; whereas the electron temperature has a slight linear decrease toward 2.2 eV. The gas density is 1021 m−3, whilst the electron density is two orders of magnitude lower. Densities follow square root relationships with arc current, with gas density decreasing whilst electron (and hence ion) density increases. Stopping and range of ions in matter calculations prove that operating a high current arc with an argon admixture is extremely difficult because cathode-coated cesium is heavily sputtered by argon.
97. The ISIS pre-injector reconfiguration
Review of Scientific Instruments 87, 02B121 (2016); http://doi.org/10.1063/1.4934658
With the introduction of a new �low energy beams� group at ISIS, the decision was taken to expand the ion source area. This paper will explain what actions were taken, how this has improved the present working environment and how the space will be used to accommodate a medium energy beam transport (MEBT) section after the existing radio-frequency quadrupole. The MEBT will incorporate three 202.5 MHz re-bunching cavities and will achieve a transmission of 96% with minimal emittance growth.
96. The mechanical design and simulation of a scaled H− Penning ion source
Review of Scientific Instruments 87, 02B131 (2016); http://doi.org/10.1063/1.4934815
The existing ISIS Penning H− source is unable to produce the beam parameters required for the front end test stand and so a new, high duty factor, high brightness scaled source is being developed. This paper details first the development of an electrically biased aperture plate for the existing ISIS source and second, the design, simulation, and development of a prototype scaled source.
95. Status of the RAL Front End Test Stand
Proceedings of IPAC2015, Richmond, VA, USA, THPF105
The Front End Test Stand (FETS) under construction at RAL is a demonstrator of front end systems for future high power proton linacs. Possible applications include a linac upgrade for the ISIS spallation neutron source, new future neutron sources, accelerator driven sub-critical systems, high energy physics proton drivers etc. Designed to deliver a 60mA H-minus beam at 3MeV with a 10% duty factor, FETS consists of a high brightness surface plasma ion source, magnetic solenoid low energy beam transport (LEBT), 4-vane 324MHz radio frequency quadrupole and medium energy beam transport (MEBT) containing a high speed beam chopper and nondestructive laser diagnostics. This paper describes the current status of the project and future plans.
94. Design Of A Scaled High Duty Factor High Current Negative Penning Surface Plasma Source
Proceedings of IPAC2015, Richmond, VA, USA, THPF104
The Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL) requires a 60 mA, 2 ms, 50 Hz H− beam. The present source can only deliver the current and pulse length requirements at 25 Hz. At 50 Hz there is too much droop in the beam current. To rectify this, a scaled source is being developed. This paper details the new source design and the experiments conducted that are guiding the design.
93. Operational and theoretical temperature considerations in a Penning surface plasma source
AIP Conference Proceedings 1655, 030013 (2015); http://doi.org/10.1063/1.4916440
A fully detailed 3D thermal model of the ISIS Penning surface plasma source is developed in ANSYS. The proportion of discharge power applied to the anode and cathode is varied until the simulation matches the operational temperature observations. The range of possible thermal contact resistances are modelled, which gives an estimation that between 67% and 85% of the discharge power goes to the cathode. Transient models show the electrode surface temperature rise during the discharge pulse for a range of duty cycles. The implications of these measurements are discussed and a mechanism for governing cesium coverage proposed. The requirements for the design of a high current long pulse source are stated.
92. Current Status of the RAL Front End Test Stand (FETS) Project
Proceedings of LINAC2012, Tel-Aviv, Israel THPB004
The UK proton accelerator strategy aims to develop a viable high power proton driver with applications including spallation neutrons, the neutrino factory and ADSR. An essential first ingredient, identified as one of the main UK R&D accelerator projects, is the Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL), aimed at producing a high quality, high current, cleanly chopped H- beam. Through its component parts, FETS has triggered development of a high brightness, 60 mA H- ion source, a three-solenoid Low Energy Beam Transport line (LEBT), a 3 MeV four-vane Radio Frequency Quadrupole (RFQ) and a Medium Energy Beam Transport line (MEBT) with a high speed chopper. The project is well advanced and when operational should be sufficiently versatile to explore a range of operating conditions. In this paper we present the current status of the construction, and plans for operation, experiments and future development.
AIP Conference Proceedings 1655, 030011 (2015); http://doi.org/10.1063/1.4916438
The UK proton accelerator strategy aims to develop a viable high power proton driver with applications including spallation neutrons, the neutrino factory and ADSR. An essential first ingredient, identified as one of the main UK R&D accelerator projects, is the Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL), aimed at producing a high quality, high current, cleanly chopped H- beam. Through its component parts, FETS has triggered development of a high brightness, 60 mA H- ion source, a three-solenoid Low Energy Beam Transport line (LEBT), a 3 MeV four-vane Radio Frequency Quadrupole (RFQ) and a Medium Energy Beam Transport line (MEBT) with a high speed chopper. The project is well advanced and when operational should be sufficiently versatile to explore a range of operating conditions. In this paper we present the current status of the construction, and plans for operation, experiments and future development.
90. Status of the FETS Project
Proceedings of LINAC2014, Geneva, Switzerland MOPP129
The Front End Test Stand (FETS) under construction at RAL is a demonstrator for front end systems of a future high power proton linac. Possible applications include a linac upgrade for the ISIS spallation neutron source, new future neutron sources, accelerator driven sub-critical systems, high energy physics proton drivers etc. Designed to deliver a 60mA H-minus beam at 3MeV with a 10%
duty factor, FETS consists of a high brightness ion source, magnetic low energy beam transport (LEBT), 4-vane 324MHz radio frequency quadrupole, medium energy beam transport (MEBT) containing a high speed beam chopper and non-destructive laser diagnostics. This paper describes the current status of the project and future plans.
89. Automated Conditioning System for Siemens Novel Electrostatic Accelerator
Proceedings of IPAC2014, Dresden, Germany THPRI027
Siemens has proposed a novel compact DC electrostatic tandem accelerator to produce protons of a few MeV and is currently commissioning a prototype at the Rutherford Appleton Laboratory. The geometry of the accelerator involves large surfaces which are exposed to high electric fields and therefore need long procedures for conditioning. An automated system for conditioning has been developed. It reacts quicker to breakdowns than a human operator could do, thus being more effective and also reduces the time spent by research staff on the conditioning.
88. Simulation Results of the FETS Laserwire Emittance Scanner
Proceedings of IPAC2014, Dresden, Germany THPME191
The Front End Test Stand (FETS) at Rutherford Appleton Laboratory (RAL) has been developed to demonstrate a high current (60 mA) H− beam with the energy of 3 MeV that will be required for future proton drivers. At such high power beam machine a non-invasive diagnostics is required. To measure the emittance of the ion beam a laserwire scanner is being developed. A low power laser will scan across the H− ion beam. The H−particles will be neutralized via a photo-detachment process producing a stream of fast neutral hydrogen atoms bearing information about the phase space distribution of the initial H− beam. To design an effective detection system and optimize its parameters a simulation of the processes at the interaction point is required. We present recent simulation results of the FETS laserwire system.
Simulations were performed using measured data of the laser propagation and ion beam distribution, obtained with General Particle Tracer code.
87. Performance of the Low Energy Beam Transport at the RAL Front End Test Stand
Proceedings of IPAC2014, Dresden, Germany THPME073
The Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL) is intended to demonstrate the early stages of acceleration (up to 3 MeV) and beam chopping required for high power proton accelerators, including proton drivers for pulsed neutron spallation sources and neutrino factories. A Low Energy Beam Transport (LEBT), consisting of three solenoids and four drift sections, is used to transport the H− beam from the ion source to the Radio Frequency Quadrupole (RFQ). We present the current performance of the LEBT with regards to beam alignment, transmission and focusing into the acceptance of the RFQ.
86. System Integration of the Demonstration Siemens Electrostatic Accelerator
Proceedings of IPAC2014, Dresden, Germany TUPME039
Siemens has proposed a novel compact DC electrostatic tandem accelerator to produce protons of a few MeV. Siemens is currently building a prototype of the accelerator at the Rutherford Appleton Laboratory. This paper reports on recent progress on the different components of the system as well as the commissioning of the whole machine.
85. Installing the VESPA H- Ion Source Test Stand at RAL
Proceedings of IPAC2014, Dresden, Germany MOPRI015
A Penning-type negative hydrogen (H� ) ion source has been used reliably on the ISIS pulsed spallation neutron and muon facility at the Rutherford Appleton Laboratory (RAL) in the UK for almost 30 years. However a detailed study of the ion source plasma and extraction has never been undertaken. If these properties were known, the beam emittance and losses due to collimation could be reduced, and the lifetime increased. This paper summarises the progress made on installing a Vessel for Extraction and Source Plasma Analyses (VESPA) to fill the knowledge gap.
84. Extracting a High Current Long Pulse Hminus Beam for FETS
Proceedings of IPAC2014, Dresden, Germany MOPRI014
The Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL) requires a 60 mA 2 ms 50 Hz H− beam. A Penning Surface Plasma Source (SPS) is used to produce the beam. This paper gives the latest results obtained using a new 25 kV long pulse extraction power supply designed and built at RAL. Power supply performance, beam current and emittance are detailed.
83. Negative Ion Sources: Magnetron and Penning
CAS - CERN Accelerator School, Ion Sources, Senec, Slovakia, 29 May - 8 Jun 2012, pp.285-310 (CERN-2013-007)
The history of the magnetron and Penning electrode geometry is briefly outlined. Plasma generation by electrical discharge-driven electron impact ionization is described and the basic physics of plasma and electrodes relevant to magnetron and Penning discharges are explained. Negative ions and their applications are introduced, along with their production mechanisms. Caesium and surface production of negative ions are detailed. Technical details of how to build magnetron and Penning surface plasma sources are given, along with examples of specific sources from around the world. Failure modes are listed and lifetimes compared.
82. Technological Aspects: High Voltage
CAS - CERN Accelerator School, Ion Sources, Senec, Slovakia, 29 May - 8 Jun 2012, pp.381-419 (CERN-2013-007)
This paper covers the theory and technological aspects of high-voltage design for ion sources. Electric field strengths are critical to understanding high-voltage breakdown. The equations governing electric fields and the techniques to solve them are discussed. The fundamental physics of high-voltage breakdown and electrical discharges are outlined. Different types of electrical discharges are catalogued and their behaviour in environments ranging from air to vacuum are detailed. The importance of surfaces is discussed. The principles of designing electrodes and insulators are introduced. The use of high-voltage platforms and their relation to system design are discussed. The use of commercially available high-voltage technology such as connectors, feedthroughs and cables are considered. Different power supply technologies and their procurement are briefly outlined. High-voltage safety, electric shocks and system design rules are covered.
Review of Scientific Instruments 85, 02B127 (2014); http://doi.org/10.1063/1.4826109
The ISIS pulsed spallation neutron and muon facility at the Rutherford Appleton Laboratory (RAL) in the UK uses a Penning surface plasma negative hydrogen ion source. Upgrade options for the ISIS accelerator system demand a higher current, lower emittance beam with longer pulse lengths from the injector. The Front End Test Stand is being constructed at RAL to meet the upgrade requirements using a modified ISIS ion source. A new 10% duty cycle 25 kV pulsed extraction power supply has been commissioned and the first meter of 3 MeV radio frequency quadrupole has been delivered. Simultaneously, a Vessel for Extraction and Source Plasma Analyses is under construction in a new laboratory at RAL. The detailed measurements of the plasma and extracted beam characteristics will allow a radical overhaul of the transport optics, potentially yielding a simpler source configuration with greater output and lifetime.
80. Matching an H� beam into a radio frequency quadrupole at Rutherford Appleton Laboratory
Review of Scientific Instruments 85, 02A745 (2014); http://doi.org/10.1063/1.4862213
A major component of work being carried out to upgrade the ISIS spallation neutron source at Rutherford Appleton Laboratory (RAL) is the Front End Test Stand (FETS). FETS is aimed at improving the luminosity of the linac, and consists of a Penning ion source, Low Energy Beam Transport (LEBT), Radio Frequency Quadrupole (RFQ), and Medium Energy Beam Transport (MEBT). It may serve as a first part of the accelerator chain providing a 60 mA, 3 MeV H� beam up to a 10% duty cycle. The current output of the source and the transmission of the LEBT are reasonable, but there are issues with the alignment to provide a centred beam matched into the acceptance of the RFQ. Improvements have been made to the post acceleration to address this problem. Measurements with a collimated beam have been performed to understand the behaviour of the solenoids and steerer magnets. Comparing these results with simulations proved that, besides possible mechanical imperfections of the ion source and post acceleration assembly, agreement can only be achieved if the magnetic fields are distorted.
Proceedings of IBIC2013, Oxford, UK TUPF06
A wire grid with 21 wires each vertically and horizontally with a spacing of 1 mm has been developed for beam analysis at Siemens� novel electrostatic accelerator. The wire grid is integrated in a Faraday Cup and profile measurements can therefore be combined with current measurements. The grid is used to analyse the 10 keV H− beam coming from the ion source and the obtained beam parameters will be used as input for simulations of the beam transport in the accelerator. All 42 wires can be read out simultaneously with a multi-channel precision electrometer and the data can be fitted instantly with LabVIEW code that was developed for this purpose. This paper reports on some details of the mechanical design and the data analysis procedure in LabVIEW as well as some results of first measurements at the novel accelerator.
78. Status of the RAL Front End Test Stand
Proceedings of IPAC2013, Shanghai, China THPWO086
The Front End Test Stand (FETS) under construction at RAL is a demonstrator for the front end systems of a future high power proton linac. Possible applications include a linac upgrade for the ISIS spallation neutron source, new future neutron sources, accelerator driven sub-critical systems, a neutrino factory etc. Designed to deliver a 60mA H-minus beam at 3MeV with a 10% duty factor, FETS consists of a high brightness ion source, magnetic low energy beam transport (LEBT), 4-vane 324MHz radio frequency quadrupole, medium energy beam transport (MEBT) containing a high speed beam chopper and non-destructive photo-detachment diagnostics. This paper describes the current status of the project and future plans
77. A New Long Pulse High Voltage Extraction Power Supply for FETS
Proceedings of IPAC2013, Shanghai, China MOPEA064
A new 25 kV 2 ms 50 Hz extraction voltage power supply has been developed for the high performance H-minus ion source for the Front End Test Stand at the Rutherford Appleton Laboratory. The power supply has been designed to fit in a single 19 inch rack and has a modular design for easy maintenance. This paper details the design and performance of the power supply.
76. Commissioning of the Ion Source for Siemens Novel Electrostatic Accelerator
Proceedings of IPAC2013, Shanghai, China MOPEA065
Siemens is developing a novel compact DC electrostatic tandem accelerator and currently building a prototype. A dedicated H- ion source for this accelerator has been designed and built. This paper reports on some of the design features as well as results of the commissioning phase of this filament driven DC multicusp volume H- ion source. Stable H- currents of more than 300 μA at 10 keV have been extracted. This satisfies the beam current requirement of the novel accelerator.
75. Investigation of Space Charge Compensation at FETS
Proceedings of IPAC2013, Shanghai, China THPWA042
In order to contribute to the development of high power proton accelerators in the MW range, to prepare the way for an ISIS upgrade and to contribute to the UK design effort on neutrino factories, a front end test stand (FETS) is being constructed at the Rutherford Appleton Laboratory (RAL) in the UK [1]. The aim of the FETS is to demonstrate the production of a 60 mA, 2 ms, 50 pps chopped beam at 3 MeV with sufficient beam quality. The ion source and LEBT are operational [2] with the RFQ being assembled and tested. As a more detailed knowledge is of interest also for other projects like ESS, LINAC4 or PIXIE the FETS LEBT was updated to perform a detailed experimental analysis of space charge compensation utilizing a pulsed decompensation electrode together with a residual gas ion energy spectrometer and a fast emittance measurement device. In the FETS LEBT a high degree of space charge compensation (~90%) and a rise time of space charge compensation around ~ 50 Psec could be concluded from measurements [2]. In this paper the results of further experimental work will be presented together with discussion of the findings.
74. Operation and thermal modeling of the ISIS H− source from 50 to 2 Hz repetition rates
AIP Conference Proceedings 1515, 114 (2013); http://doi.org/10.1063/1.4792777
CERN's Linac4 accelerator H− ion source, currently under construction, will operate at a 2 Hz repetition rate, with pulse length of 0.5 ms and a beam current of 80 mA. Its reliability must exceed 99 % with a mandatory 3 month uninterrupted operation period. A Penning ion source is successfully operated at ISIS; at 50 Hz repetition rate it reliably provides 55 mA H− pulses of 0.25 ms duration over 1 month. The discharge plasma ignition is very sensitive to the temperatures of the discharge region, especially of its cathode. The investigation by modeling and measurement of operation parameters suitable for arc ignition and H− production at 2 Hz is of paramount importance and must be understood prior to the implementation of discharge ion sources in the Linac4 accelerator. In its original configuration, the ISIS H− source delivers beam only if the repetition rate is above 12.5 Hz, this paper describes the implementation of a temperature control of the discharge region aiming at lower repetition rate operation. The experimental results of the modified source successfully operated down to 1.6 Hz and providing 30 mA H− pulses of 0.75 ms duration are presented. A thermal modeling of the ISIS ion source gives insight to the relevant parameters. The analysis demonstrates the adaptability of discharge sources for the operating conditions of the Linac4.
73. Developing the RAL front end test stand source to deliver a 60 mA, 50 Hz, 2 ms H− beam
AIP Conference Proceedings 1515, 359 (2013); http://doi.org/10.1063/1.4792804
All the Front End Test Stand (FETS) beam requirements have been achieved, but not simultaneously [1]. At 50 Hz repetition rates beam current droop becomes unacceptable for pulse lengths longer than 1 ms. This is fundamental limitation of the present source design. Previous researchers [2] have demonstrated that using a physically larger Penning surface plasma source should overcome these limitations. The scaled source development strategy is outlined in this paper. A study of time-varying plasma behavior has been performed using a V-UV spectrometer. Initial experiments to test scaled plasma volumes are outlined. A dedicated plasma and extraction test stand (VESPA-Vessel for Extraction and Source Plasma Analysis) is being developed to allow new source and extraction designs to be appraised. The experimental work is backed up by modeling and simulations. A detailed ANSYS thermal model has been developed. IBSimu is being used to design extraction and beam transport. A novel 3D plasma modeling code using beamlets is being developed by Cobham Vector Fields using SCALA OPERA, early source modeling results are very promising. Hardware on FETS is also being developed in preparation to run the scaled source. A new 2 ms, 50 Hz, 25 kV pulsed extraction voltage power supply has been constructed and a new discharge power supply is being designed. The design of the post acceleration electrode assembly has been improved.
72. Potential for improving of the compact surface plasma sources
AIP Conference Proceedings 1515, 369 (2013); http://doi.org/10.1063/1.4792805
Factors limiting the operating lifetime of Compact Surface Plasma Sources (CSPS) are analyzed and possibilities for lifetime enhancement are considered. Noiseless discharges with lower gas and cesium densities are produced in experiments with a modified discharge cell. With these discharge cells it is possible to increase the emission aperture and extract the same beam with low enough emittance from a lower current discharge with a corresponding increase in source lifetime. A design of advanced CSPS for production of H− beam with average current up to 20 mA (with pulsed current up to 0.1 A) and extrapolated integrated beam lifetime ∼10 A hours is presented.
71. Design study of a test vessel to investigate the ISIS H− Penning ion source plasma
AIP Conference Proceedings 1515, 440 (2013); http://doi.org/10.1063/1.4792814
A vacuum-vessel for extraction and source plasma analyses (VESPA) has been constructed with the aim of understanding the dominant plasma processes of negative hydrogen (H−) ion formation in the ISIS Penning ion source. The VESPA has been designed to be simple and inexpensive, with all features of the ISIS ion source not directly responsible for plasma formation removed such that there is ample space for diagnostics close to the plasma. Diagnostics will include but are not limited to a beam current density monitor, a high resolution visible-light monochromator, a cesium mass deposition monitor, an electrostatic energy analyser, a magnetic mass spectrometer and an emittance scanner. Several existing parts and ancillary equipment are re-used to reduce costs and to speed up installation. The ultimate aim of the VESPA is to perform detailed analyses of the H− production, cesium usage and beam formation such that an upgrade to the ion source is both well informed and possible using this setup. This report details the design philosophy, results of initial testing and future plans.
70. Upgrade of the ITUR extraction system at ESS-Bilbao
AIP Conference Proceedings 1515, 587 (2013); http://doi.org/10.1063/1.4792831
The first beam measurements on our modified version of the ISIS Penning source show a beam of relatively low current. As a result of this, the actual extraction system was simulated using IBSimu, and it was found that the configuration is far from the optimal case. We present a simpler post-acceleration extraction system that avoids the use of a long (∼100mm) Cs trap. Due to space and budget constraints, the new extraction is composed of only one electrostatic einzel lens. The same configuration, as the ISIS source, is maintained up to the puller electrode; the changes come afterwards, where two circular electrodes with rectangular apertures make up the einzel lens. This configuration lacks the bending magnet found at ISIS because the permanent magnets used in this version of the source provide the Penning field. This difference results in a low angle beam extraction that is compensated by tilting the source to angles near 15�. In addition to the beam dynamics simulations, the mechanical and electrostatic simulations for the extraction system are presented.
69. Current Status of the RAL Front End Test Stand (FETS) Project
Proceedings of LINAC2012, Tel-Aviv, Israel THPB004
The UK proton accelerator strategy aims to develop a viable high power proton driver with applications including spallation neutrons, the neutrino factory and ADSR. An essential first ingredient, identified as one of the main UK R&D accelerator projects, is the Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL), aimed at producing a high quality, high current, cleanly chopped H- beam. Through its component parts, FETS has triggered development of a high brightness, 60 mA H- ion source, a three-solenoid Low Energy Beam Transport line (LEBT), a 3 MeV four-vane Radio Frequency Quadrupole (RFQ) and a Medium Energy Beam Transport line (MEBT) with a high speed chopper. The project is well advanced and when operational should be sufficiently versatile to explore a range of operating conditions. In this paper we present the current status of the construction, and plans for operation, experiments and future development.
68. Workshop on performance variations in H− ion sources 2012: PV H−12
AIP Conference Proceedings 1515, 594 (2013); http://doi.org/10.1063/1.4792832
This paper briefly summarizes a workshop held in Jyvaskyla the day after NIBS�12. The half-day workshop aimed at globally capturing the issue of performance variations in H− sources. There was a focus on production facilities and facilities that work under production-like conditions, because there are often high expectations to be met.
67. Ion Sources for High-Power Hadron Accelerators
CAS - CERN Accelerator School: Course on High Power Hadron Machines, Bilbao, Spain, 24 May - 2 Jun 2011, pp.369-407 (CERN-2013-001)
http://doi.org/10.5170/CERN-2013-001.369
Ion sources are a critical component of all particle accelerators. They create the initial beam that is accelerated by the rest of the machine. This paper will introduce the many methods of creating a beam for high-power hadron accelerators. A brief introduction to some of the relevant concepts of plasma physics and beam formation is given. The different types of ion source used in accelerators today are examined. Positive ion sources for producing H+ ions and multiply charged heavy ions are covered. The physical principles involved with negative ion production are outlined and different types of negative ion sources are described. Cutting edge ion source technology and the techniques used to develop sources for the next generation of accelerators are discussed.
66. Investigation of Space Charge Compensation at FETS
Proceedings of IPAC2012, May 2012
In order to contribute to the development of high power proton accelerators in the MW range, to prepare the way for an ISIS upgrade and to contribute to the UK design effort on neutrino factories, a front end test stand (FETS) is being constructed at the Rutherford Appleton Laboratory (RAL) in the UK. The aim of the FETS is to demonstrate the production of a 60 mA, 2 ms, 50 pps chopped beam at 3 MeV with sufficient beam quality. The ion source and LEBT are operational with the RFQ under manufacture. In the LEBT a high degree of space charge compensation (~90%) and a rise time of space charge compensation around ~ 50 microsec could be concluded indirectly from measurements . As a more detailed knowledge is of interest also for other projects like ESS the FETS LEBT was updated to perform a detailed experimental analysis of space charge compensation. In this paper the results of the experimental work will be presented together with discussion of the findings in respect to beam transport.
65. Lifetime of the Highly Efficient H- Ion Sources
Proceedings of IPAC2012, May 2012
Factors limiting operating lifetime of Compact Surface Plasma Sources (CSPS) are analyzed and possible treatments for lifetime enhancement are considered. CSPSs have high plasma density (up to 1014 cm-3), high emission current density of negative ions (up to 8 A/cm2), small (1�5 mm) gap between cathode emitter, and a small extraction aperture in the anode. They are very simple, have high energy efficiency up to {10}0 mA/kW of discharge (~{10}0 times higher then modern large Volume RF SPS) and have a high gas efficiency (up to 30%) using pulsed valves. CSPSs are very good for pulsed operation but electrode power density is often too high for dc operation. However, CSPSs were successfully adopted for DC operation with emission current density ~300 mA/cm2 in Hollow cathode Penning Discharge and up to 1 A/cm2 in Spherical focusing semiplanotron. Flakes from electrodes sputtering and blistering induced by back accelerated positive ions are the main reasons of ion source failure. Suppression of back accelerated positive ions, flakes explosion by pulsed discharges, and flakes gasification by discharge in NF_3 (or XeF_2) can be used for significant increase of operating lifetime of CSPSs.
64. Status of the RAL Front End Test Stand [ kB]
Proceedings of IPAC2012, May 2012
The Front End Test Stand (FETS) under construction at RAL is a demonstrator for front end systems of a future high power proton linac. Possible applications include a linac upgrade for the ISIS spallation neutron source, new future neutron sources, accelerator driven sub-critical systems, a neutrino factory etc. Designed to deliver a 60mA H-minus beam at 3MeV with a 10% duty factor, FETS consists of a high brightness ion source, magnetic low energy beam transport (LEBT), 4-vane 324MHz radio frequency quadrupole, medium energy beam transport (MEBT) containing a high speed beam chopper plus comprehensive diagnostics. This paper describes the current status of the project and future plans.
63. Optimizing the Front End Test Stand High Performance H- Ion Source at RAL [1225 kB]
Review of Scientific Instruments 83, 02A701 (2012)
The aim of the front end test stand project is to demonstrate that chopped low energy H− beams of high quality can be produced. The beam line currently consists of the ion source, a 3 solenoid low energy beam transport and a suite of diagnostics. A brief status report of the radio frequency quadrupole is given. This paper details the work to optimize the ion source performance. A new high power pulsed discharge power supply with greater reliability has been developed to allow long term, stable operation at 50 Hz with a 60 A, 2.2 ms discharge pulse and up to 100 A at 1.2 ms. The existing extraction power supply has been modified to operate up to 22 kV. Results from optical spectroscopy measurements and their application to source optimization are summarized. Source emittances and beam currents of 60 mA are reported.
62. Status of the CERN plasma generator of the Superconducting Proton Linac [1255 kB]
Review of Scientific Instruments 83, 02A703 (2012)
In the framework of the superconducting proton linac (SPL) study at CERN, a new non-cesiated H− plasma generator driven by an external 2 MHz RF antenna has been developed and successfully operated at repetition rates of 50 Hz, pulse lengths of up to 3 ms, and average RF powers of up to 3 kW. The coupling efficiency of RF power into the plasma was determined by the cooling water temperatures and the analysis of the RF forward and reflected power and the antenna current and
amounts to 50%�60%. The plasma resistance increases between 10 kW and 40 kW RF power from about 0.45 Ohms to 0.65 Ohms. Measurements of RF power dissipated in the ferrites and the magnets on a test bench show a 5-fold decrease of the power losses for the magnets when they are contained in a Cu box, thus validating the strategy of shielding the magnets with a high electrical conductivity material. An air cooling system was installed in the SPL plasma generator to control the temperatures of the ferrites despite hysteresis losses of several Watts.
61. Investigation of ISIS and BNL ion source electrodes after extended operation [1166 kB]
Review of Scientific Instruments 83, 02A728 (2012)
CERN�s Linac4 accelerator is under construction and a RF driven H- ion source is being developed. The beam current requirement for Linac4 is very challenging: 80 mA must be provided. Cesiated plasma discharge ion sources such as Penning or magnetron sources are also potential candidates. Accelerator ion sources must achieve typical reliability figures of 95% and above. Investigating and understanding the underlying mechanisms involved with source failure or ageing is critical when selecting the ion source technology. Plasma discharge ion sources rely on molybdenum cathodes. Deformation of the cathode surfaces is visible after extended operation periods. A metallurgical investigation of an ISIS ion source is presented. The origin of the deformation is twofold: Molybdenum sputtering by cesium ions digs few tenths of mm cavities while an epitaxial growth of molybdenum is observed in the immediate vicinity. The molybdenum growth under hydrogen atmosphere is hard and loosely bound to the bulk. It is therefore likely to peel off and be transported within the plasma volume. The observation of the cathode, anode and extraction electrodes of the Magnetron source operated at BNL for two years are presented. A beam simulation of H-, electrons and Cs-ions was performed with the IBSimu code package to qualitatively explain the observations. This paper describes the operation conditions of the ion sources, and discusses the metallurgical analysis and beam simulation results.
60. Initial Study of the Optical Spectrum of the ISIS H- Ion Source Plasma [1599 kB]
Review of Scientific Instruments 83, 02A704 (2012)
The Front End Test Stand (FETS) is being constructed at the Rutherford Appleton Laboratory (RAL), with the aim of producing a 60 mA, 2 ms, 50 Hz, perfectly chopped H- ion beam. To meet the beam requirements, a more detailed understanding of the ion source plasma is required. To this end, an initial study is made of the optical spectrum of the plasma using a digital spectrometer. The atomic and molecular emission lines of hydrogen and caesium are clearly distinguished and a quantitative comparison is made when the ion source is run in different conditions. The electron temperature is 0.6 eV and measured line widths vary by up to 75%.
59. H- beam transport experiments in a solenoid-LEBT [1610 kB]
Review of Scientific Instruments 83, 02B719 (2012)
The Front End Test Stand (FETS) is located at Rutherford Appleton Laboratory and aims for a high current, fast chopped 3 MeV H� ion beam suitable for future high power proton accelerators like ISIS upgrade. The main components of the front end are the Penning ion source, a low energy beam transport line, an radio-frequency quadrupole (RFQ) and a medium energy beam transport (MEBT)providing also a chopper section and rebuncher. FETS is in the stage of commissioning its low energy beam transport (LEBT) line consisting of three solenoids. The LEBT has to transport an H� high current beam (up to 60 mA) at 65 keV. This is the injection energy of the beam into the RFQ.
The main diagnostics are slit�slit emittance scanners for each transversal plane. For optimizing the matching to the RFQ, experiments have been performed with a variety of solenoid settings to better understand the actual beam transport. Occasionally, source parameters such as extractor slit width and beam energy were varied as well. The paper also discusses simulations based on these measurements.
58. Latest Results from the Front End Test Stand High Performance H- Ion Source at RAL [720 kB]
Proceedings of NIBS2010, November 2010
The aim of the Front End Test Stand (FETS) project is to demonstrate that chopped low energy beams of high quality can be produced. FETS consists of a high power Penning Surface Plasma Ion Source, a 3 solenoid LEBT, a 3 MeV RFQ, a chopper and a comprehensive suite of diagnostics. This paper briefly outlines the status of the project, hardware installation and modifications. Results from experiments running the H- ion source at 2 ms pulse length are detailed: the discharge current is varied between 20 A and 50 A. The discharge repetition rate is varied between 12.5 and 50 Hz. Hydrogen and Caesium vapour flow rates are varied. The effect of electrode surface temperature and beam current droop are discussed. Peak beam currents of over 60 mA for 2 ms pulse length can be achieved. Normalised r.m.s emittances of 0.3 πmm.mrads at the exit of the LEBT are presented for different source conditions.
57. First LEBT Simulations For The Bilbao Accelerator Ion
Source Test Stand [674 kB]
Proceedings of 46th ICFA Advanced Beam Dynamics Workshop on High-Intensity and High-Brightness Hadron Beams, October 2010
The proposed multi-specimen Low Energy Transport System (LEBT) consists of a series of solenoids with tunable magnetic fields, used to match the characteristics of
the beam to those imposed by the RFQ input specification. The design of the LEBT involves selecting the number of solenoids to use and their fixed positions, so that a set of fields that provides the desired matching can be found for any given conditions (different currents, input emittances, etc). In this work we present the first simulations carried out to design the Bilbao Accelerator LEBT, which were performed using several codes (TRACK, GPT, Trace2D). The best configuration is discussed and evaluated in terms of the degree of matching to the RFQ input requirements.
56. The Development of the H- Ion Source Test Stand for CSNS [915 kB]
Proceedings of LINAC10, September 2010
The type of the H- ion source chosen for the China Spallation Neutron Source (CSNS) is the Penning surface plasma source. The designed output energy of the source is 50 keV and the pulsed beam current of H- beam is 20 mA with a rms. emittance of 0.2 πmm.mrad. The construction of the H- ion source test stand for CSNS is complete and commissioning of the source is in progress. Stable H- ion beams with currents up to 50 mA and energies of 50 keV are achieved. Emittance measurement of the beam is also being prepared.
55. Status of the FETS Commissioning and Comparison with Particle Tracking Results [1970 kB]
Proceedings of LINAC10, September 2010
In order to contribute to the development of high power proton accelerators in the MW range, to prepare the way for an ISIS upgrade and to contribute to the UK design effort on neutrino factories, a front end test stand (FETS) is being constructed at the Rutherford Appleton Laboratory (RAL) in the UK. The aim of the FETS is to demonstrate the production of a 60 mA, 2 ms, 50 pps chopped beam at 3 MeV with sufficient beam quality. The status of the FETS will be given and experimental results from the commissioning of LEBT and ion source will be presented. Previous measurements showed that the emittance of the beam delivered by the ion source exceeded our expectations by more than a factor of 3. Since then various changes in the beam extraction/post accelerator region reduced the beam emittance more than a factor of 2. The results from measurements will be compared with numerical simulations of the particle dynamics from the ion source to the end of the MEBT and the results discussed in respect to further work.
54. Pulse Lengthening Experiments on the FETS Ion Source [997 kB]
Proceedings of IPAC10, May 2010
The Front End Test Stand (FETS) under construction at the Rutherford Appleton Laboratory is the UK's contribution to research into the next generation of High
Power Proton Accelerators (HPPAs). Running at 50 Hz with 2 ms pulse lengths are required. This paper presents initial H- beam currents for long pulse lengths.
53. Assessing the Transmission of the H- Ion Beam on the Front End Test Stand [947 kB]
Proceedings of IPAC10, May 2010
The front end test stand (FETS) is entering the next stage of construction and commissioning, with the threesolenoid magnetic low energy beam transport (LEBT)
line being installed. A thorough characterization of the beam leaving the Penning H- ion source has been performed. This includes measurements of the beam
current using toroids and of the transverse emittance using slit-slit scanners. These measurements are performed over a wide range of source discharge and
extraction parameters in order to understand how the transmission may be improved. Comments on the quality of the beam to be injected into the FETS radio frequency
quadrupole (RFQ) are given.
52. Status of the RAL Front End Test Stand [472 kB]
Proceedings of IPAC10, May 2010
The Front End Test Stand (FETS) under construction at the Rutherford Appleton Laboratory is the UK's contribution to research into the next generation of High
Power Proton Accelerators (HPPAs). HPPAs are an essential part of any future Spallation Neutron Source, Neutrino Factory, Muon Collider, Accelerator Driven
Sub-critical System, Waste Transmuter etc. FETS will demonstrate a high quality, high intensity, chopped Hminus beam and is a collaboration between RAL,
Imperial College and the Universtity of Warwick in the UK and the Universidad del Pais Vasco and ESS-Bilbao in Spain. This paper describes the current status and
future plans of FETS.
51. Commissioning of the Low Energy Beam Transport of the Front End Test Stand [1120 kB]
Proceedings of IPAC10, May 2010
The Front End Test Stand (FETS) at the Rutherford Appleton Laboratory is intended to demonstrate the early stages of acceleration (0-3 MeV) and beam chopping required for high power proton accelerators, including proton drivers for pulsed neutron spallation sources and neutrino factories. A Low Energy Beam Transport (LEBT), consisting of three solenoids and four drift sections, is used to
transport the H− beam from the ion source to the FETS Radio Frequency Quadrupole. We present the status of the installation and commissioning of the LEBT, and compare particle dynamics simulations with preliminary measurements of the H− beam transport through the LEBT.
50. Beam Stop Design and Construction for the Front End Test Stand at ISIS [1060 kB]
Proceedings of IPAC10, May 2010
A Front End Test Stand is being built at the Rutherford Appleton Laboratory in the UK to demonstrate a chopped H− beam of sufficiently high beam quality for future highpower proton accelerators (HPPA). The test stand consists
of a negative hydrogen ion source, a 3 solenoid LEBT, a 324 MHz four vane RFQ, a MEBT composed of rebunching cavities and choppers and a set of diagnostics
ending with a beam stop. The beam stop, which has to accept a 3 MeV, 60 mA, 2 ms, 50 Hz (10% duty factor) H− beam, consists of a coaxial double cone configuration
where the inner cone's inner surface is hit by the beam and the inter-cone gap is cooled by high-speed water. In order to minimize both prompt and induced radiation pure aluminium is used, but the poor mechanical properties of pure aluminium are overcome by employing a metal spinning process that increases the yield strength to several times the original value of the non-deformed material.
49. First Simulation Tests for the Bilbao Accelerator Ion Source Test Stand [1364 kB]
Proceedings of IPAC10, May 2010
The rationale behind the Bilbao Accelerator Ion Source Test Stand (ITUR) project [1] is to perform a comparison between different kinds of hydrogen ion sources using the same beam diagnostics setup. In particular, a direct comparison
will be made in terms of the emittance characteristics of Penning-type sources such as those currently being used in ISIS (UK) and those of microwave type such as
CEA-Saclay and INFN. The aim here pursued is to build an Ion Source Test Stand where virtually any type of source can be tested and, thus, compared to the results of other sources under the same gauge. It would then be possible to establish a common ground for effectively comparing different ion sources. The work here presented reports on the first simulations for the H− extraction system, as well the devices that conform the diagnostic vessel: Faraday Cup, Pepperpot and Retarding Potential Analyzer (RPA), among others.
48. The Front End Test Stand High Performance H- Ion Source at RAL [453 kB]
Review of Scientific Instruments, Volume 81, Issue 2, 2010
The aim of the Front End Test Stand (FETS) project is to demonstrate that chopped low energy beams of high quality can be produced. FETS consists of a 60 mA Penning Surface Plasma Ion Source, a 3 solenoid LEBT, a 3 MeV RFQ, a chopper and a comprehensive suite of diagnostics. This paper details the design and initial performance of the ion source and the laser profile measurement system. Beam current, profile and emittance measurements are shown for different operating conditions.
47. High duty factor Plasma Generator for CERN�s Superconducting Proton Linac [464 kB]
Review of Scientific Instruments, Volume 81, Issue 2, 2010
CERN�s Linac4 is a 160 MeV linear accelerator. Currently being installed, it will inject negatively charged hydrogen ions into CERN�s PS‐Booster. The ion‐source of Linac4 is a non‐caesiated RF driven H‐ volume source directly inspired from the one of DESY and will deliver pulses of 80 mA of H‐ during 0.4 ms at a 2 Hz repetition rate. The Superconducting Proton Linac (SPL) is a major upgrade of Linac4 up to 5 GeV that is part of the luminosity upgrade of the LHC and foreseen to deliver H‐ ions or protons after stripping, i.e. to a future 50 GeV Synchrotron.
For the SPL high power option (HP‐SPL) that will deliver pulses of 80 mA of H‐ during 1.2 ms and operate at a 50 Hz repetition rate, the peak power of the 2 MHz RF is 100 kW and the duty factor of the ion source will be 6 %. This is significantly higher than the ion‐source of Linac4 (0.08 %). The development of a new water cooled plasma generator for the SPL ion‐source is presented in this paper. The plasma generator engineering is based on the results of a thermal study with a finite element model of the Linac4 H‐ plasma generator to identify components and thermal links that are critical in terms of heat transportation. The plasma generator is split into three parts with different functionalities, namely the ignition region or electron‐gun, the plasma chamber (including multi cusp and antenna) and the extraction region. For each of them, a cooling system is proposed which achieves the required heat dissipation and maintains the original functionality. New materials with higher thermal conductivity were selected and, wherever possible, thermal barriers resulting from low pressure contacts were
removed by brazing. The design of the AlN plasma chamber cooling circuit for is inspired from the approach chosen for the cesiated high duty factor RF H‐ source operating at SNS.
46. Finite element thermal study of the Linac4 plasma generator [223 kB]
Review of Scientific Instruments, Volume 81, Issue 2, 2010
The Superconducting Proton Linac (SPL) plays an important role in a future upgrade of the CERN accelerator complex. This device is proposed to deliver beam to the future Proton Synchrotron (PS2), and will allow an increase in the beam brightness for LHC. The LP‐SPL (low‐power SPL) uses an extension of the currently built Linac4 as front‐end, increasing the energy to a maximum of 5 GeV. The HP‐SPL (high power SPL) option increases the duty cycle from about 0.1% to several percent, which would open physics possibilities for super‐beams for neutrino production, muon production for a neutrino factory, or increased radio isotope production. This increase in repetition rate demands the development of a new RF powered H‐ source. In particular, this source needs to withstand the high thermal load experienced in the HP‐SPL mode, which will be up to 75 times higher than in the nominal operation mode of Linac4. This work presents the results of a thermal study of a finite element model of the plasma generator of the non‐cesiated Linac4 H‐ ion source, which is a slightly adapted version of the DESY‐HERA RF plasma generator. It is shown that the equilibrium temperatures obtained in the Linac4 maximum operation mode (100 kW RF power, 2 Hz, 0.4 ms pulse duration) are within material specifications except from the magnet cage, where a redesign may be necessary. To assess the upgrade of the Linac4 source for operation in SPL, an extrapolation of the heat load towards the high‐power option of the SPL nominal operation mode (100 kW RF power, 50 Hz, pulse duration 1.2 ms) has been performed. The results indicate the major improvements of the source cooling that are required to allow for operation in SPL.
45. Diagnostic Experiments on a 3MeV H- Test Stand at Rutherford Lab (UK) [1026 kB]
Review of Scientific Instruments, Volume 81, Issue 2 , 2010
A front end is currently under construction consisting of an H- Penning ion source
(70keV, 50mA), LEBT and RFQ (3MeV output energy) with a MEBT usable for high
power proton applications. The transport sections and their diagnostics either used during commissioning (e.g. beam profile monitor, pepperpot, slit-slit emittance scanner) or permanently installed (preferable non�destructive like photo-detachment based techniques) are crucial to fulfill all specifications. One possibility to determine beam distributions is a longitudinal movable scintillator with CCD camera. First experiments have been performed to control the beam injection into the LEBT. The influence of beam parameters like particle energy and space charge compensation on the 2D distribution and profiles will be presented.
44. Plasma Meniscus and Extraction Electrode Studies
of the ISIS H- Ion Source [403 kB]
Review of Scientific Instruments, Volume 81, Issue 2 , 2010
In order to reduce the emittance and increase the transported beam current from the ISIS Penning H- ion source, the extraction system must be improved. This ion source is currently being commissioned on the Front End Test Stand (FETS), which demands higher extraction energies, higher beam currents and smaller emittances. In order to facilitate this, the present geometry must be optimized. This paper details the studies performed on the shape of the plasma meniscus and the possible electrode geometry modifications needed to extract the highest quality beam.
43. Data Acquisition and Error Analysis for Pepperpot Emittance Measurements [1160 kB]
Proceedings of DIPAC09, May 2009
The pepperpot provides a unique and fast method of measuring emittance, providing four dimensional correlated beam measurements for both transverse planes. In
order to make such a correlated measurement, the pepperpot must sample the beam at specific intervals. Such discontinuous data, and the unique characteristics of the pepperpot assembly, requires special attention be paid to both the data acquisition and the error analysis techniques. A first-principles derivation of the error contribution to the rms emittance is presented, leading to a general formula for emittance error calculation. Two distinct pepperpot systems, currently in use at GSI in Germany and RAL in the UK, are described. The data acquisition process for each system is detailed, covering the reconstruction of the beam profile and the transverse emittances. Error analysis for both systems is presented, using a number of methods to estimate the emittance and associated errors.
42. Mechanical Engineering for the Front End Test Stand [3304 kB]
Proceedings of PAC09, May 2009
The RAL Front End Test Stand (FETS) is being constructed to demonstrate a chopped H− ion beam of up to 60 mA at 3 MeV with 50 pps and sufficiently high beam quality for future high-power proton accelerators (HPPA). This paper details the mechanical engineering components related to ion source high voltage cage, the post acceleration electrode and the laser based beam diagnostics that immediately follow the ion source.
41. Initial Results from the Front End Test Stand High Performance H- Ion Source at RAL [562 kB]
Proceedings of PAC09, May 2009
The RAL Front End Test Stand (FETS) is being constructed to demonstrate a chopped H- beam of up to 60 mA at 3 MeV with 50 pps and sufficiently high beam quality for future high-power proton accelerators (HPPA). High power proton accelerators with beam powers in the several megawatt range have many applications including drivers for spallation neutron sources, neutrino factories, waste transmuters and tritium production facilities. The aim of the FETS project is to demonstrate that chopped low energy beams of high quality can be produced and is intended to allow generic experiments exploring a variety of operational conditions. This paper details the first results from the initial operation of the ion source.
40. A Test Stand for Ion Sources of Ultimate Reliability [494 kB]
AIP Conf. Proc. Volume 1097, pp. 461-469. Proceedings of the 1st International Symposium on Negative Ions, Beams and Sources March 12, 2009
The rationale behind the ITUR project is to perform a comparison between different kinds of H− ion sources using the same beam diagnostics setup. In particular, a direct comparison will be made in terms of the emittance characteristics of Penning Type sources such as those currently in use in the injector for the ISIS (UK) Pulsed Neutron Source and those of volumetric type such as that driving the injector for the ORNL Spallation Neutron Source (TN, U.S.A.). The endeavour here pursued is thus to build an Ion Source Test Stand where virtually any type of source can be tested and its features measured and, thus compared to the results of other sources under the same gauge. It would be possible then to establish a common ground for effectively comparing different ion sources. The long term objectives are thus to contribute towards building compact sources of minimum emittance, maximum performance, high reliability-availability, high percentage of desired particle production, stability and high brightness. The project consortium is lead by Tekniker-IK4 research centre and partners are companies Elytt Energy and Jema Group. The technical viability is guaranteed by the collaboration between the project consortium and several scientific institutions, such the CSIC (Spain), the University of the Basque Country (Spain), ISIS (STFC-UK), SNS (ORNL-USA) and CEA in Saclay (France).
39. Redesign of the Analysing Magnet in the ISIS H− Penning Ion Source [315 kB]
AIP Conf. Proc. Volume 1097, pp. 253-262. Proceedings of the 1st International Symposium on Negative Ions, Beams and Sources March 12, 2009
A full 3D electromagnetic finite element analysis and particle tracking study is undertaken of the ISIS Penning surface plasma H− ion source. The extraction electrode, 90� analysing magnet, post-extraction acceleration gap and 700 mm of drift space have been modelled in CST Particle Studio 2008 to study the beam acceleration and transport at all points in the system. The analyzing magnet is found to have a sub-optimal field index, causing beam divergence and contributing the beam loss. Different magnet pole piece geometries are modelled and the effects of space charge investigated. The best design for the analysing magnet involves a shallower intersection angle and larger separation of the pole faces. This provides radial focusing to the beam, leading to less collimation. Three new sets of magnet poles are manufactured and tested on the Ion Source Development Rig to compare with predictions.
38. Commissioning the Front End Test Stand High Performance H− Ion Source at RAL [708 kB]
AIP Conf. Proc. Volume 1097, pp. 243-252. Proceedings of the 1st International Symposium on Negative Ions, Beams and Sources March 12, 2009
The RAL Front End Test Stand (FETS) is being constructed to demonstrate a chopped H- beam of up to 60 mA at 3 MeV with 50 p.p.s. and sufficiently high beam quality for future high-power proton accelerators (HPPA). High power proton accelerators with beam powers in the several megawatt range have many applications including drivers for spallation neutron sources, neutrino factories, waste transmuters and tritium production facilities. The aim of the FETS project is to demonstrate that chopped low energy beams of high quality can be produced and is intended to allow generic experiments exploring a variety of operational conditions. This paper details the first stage of construction- the installation and commissioning of the ion source. Initial performance figures are reported.
37. Multi-beamlet Study of Beam Transport in the ISIS H- Ion Source Analysing Magnet [543 kB]
Proceedings of EPAC08, June 2008
The RAL Front End Test Stand (FETS) is being constructed to demonstrate a chopped H- beam of up to 60 mA at 3 MeV with 50 pps and sufficiently high beam quality for future high-power proton accelerators (HPPA). The existing 90� analysing magnet on the ISIS H- Penning ion source does not perfectly transport the beam after extraction. The present ion source has a 10 mm x 0.6 mm slit extraction aperture. To understand how the beam is transported in the analysing magnet, new ion source aperture plates are manufactured with 5 individual holes instead of a slit. These holes produce separate beamlets that are used to study transport in the sector magnet. This paper details the experiments with the modified aperture plates on the Ion Source Development Rig (ISDR) at ISIS.
36. Study of the Post Extraction Acceleration Gap in the ISIS H- Penning Ion Source [738 kB]
Proceedings of EPAC08, June 2008
The RAL Front End Test Stand (FETS) is being constructed to demonstrate a chopped H- beam of up to 60 mA at 3 MeV with 50 pps and sufficiently high beam quality for future high-power proton accelerators (HPPA). The injection energy into the RFQ will be in the range of 50 to 70 keV whereas the standard ISIS H- Penning ion source operates at 35 keV, therefore the post extraction acceleration voltage must be increased. In order to finalise the design of the FETS post extraction system, a study is conducted on the Ion Source Development Rig (ISDR) at ISIS. This study shows how beam transport is affected by different post extraction acceleration voltages and gap lengths. Beam, current, profile and emittance measurements are presented along with theoretical calculations.
35. Installation of the Front End Test Stand High Performance H- Ion Source at RAL [353 kB]
Proceedings of EPAC08, June 2008
The RAL Front End Test Stand (FETS) is being constructed to demonstrate a chopped H− beam of up to 60 mA at 3 MeV with 50 pps and sufficiently high beam quality for future high-power proton accelerators (HPPA). This paper details the first stage of construction- the installation of the ion source.
34. Modifications to the Analysing Magnet in the ISIS Penning Ion Source [387 kB]
Proceedings of EPAC08, June 2008
A full 3D electromagnetic finite element analysis and particle tracking study has been undertaken of the ISIS Penning surface plasma ion source using CST Particle Studio 2008. The existing 90� analysing magnet is found to have a sub-optimal magnetic field index, causing beam divergence and contributing to beam loss. Different magnet pole piece geometries are modelled and the effect of space charge investigated. Based on this modelling, three new sets of poles are manufactured and tested on the Ion Source Development Rig.
33. Improving the ISIS Emittance Scanner Software [157 kB]
Proceedings of EPAC08, June 2008
The software to drive the slit-slit emittance scanners at ISIS has been re-written in C#. The scan routine has been enhanced to improve accuracy, and to allow real-time monitoring of the scanning procedure. A multiple document interface allows quick comparison with other measurements and with data from particle tracking codes. Integrated data processing and emittance calculation removes the need to transfer data between multiple software packages, making experimental work more efficient. A user-friendly and robust interface allows easy scanning and generates publication quality emittance plots for presentations.
32. Status of the RAL Front End Test Stand [207 kB]
Proceedings of EPAC08, June 2008
High power proton accelerators (HPPAs) with beam powers in the several megawatt range have many applications including drivers for spallation neutron sources, neutrino factories, waste transmuters and tritium production facilities. The UK's commitment to the development of the next generation of HPPAs is demonstrated by a test stand being constructed in collaboration between RAL, Imperial College London, the University of Warwick and the Universidad del Pais Vasco, Bilbao. The aim of the RAL Front End Test Stand is to demonstrate that chopped low energy beams of high quality can be produced and is intended to allow generic experiments exploring a variety of operational conditions. This paper describes the current status of the RAL Front End Test Stand.
31. Understanding Extraction and Beam Transport in the ISIS H− Penning Surface Plasma Ion Source [391kB]
Review of Scientific Instruments Volume 79, Number 1, 2008
The ISIS particle accelerator H− Penning surface plasma source has been developed to produce beam currents up to 70 mA and pulse lengths up to 1.5 ms at 50 Hz. This paper details the investigation into beam extraction and beam transport in an attempt to understand the beam emittance and to try to improve the emittance. A scintillator profile measurement technique has been developed to assess the performance of different plasma electrode apertures, extraction electrode geometries, and post extraction acceleration configurations. This work shows that the present extraction, beam transport, and post acceleration system are suboptimal and further work is required to improve it.
30. Status Report on the RAL Front End Test Stand [266 kB]
Proceedings of PAC07, June 2007
High power proton accelerators (HPPAs) with beam powers in the several megawatt range have many particle accelerator applications including drivers for spallation neutron sources [1], neutrino factories [2], waste transmuters and tritium production facilities. The UK's commitment to the development of the next generation of HPPAs is demonstrated by a test stand being constructed in collaboration between RAL, Imperial College London, the University of Warwick and the Universidad del Pais Vasco. The aim of the RAL Front End Test Stand is to demonstrate that chopped low energy beams of high quality can be produced and is intended to allow generic experiments exploring a variety of operational conditions. This paper describes the status of the RAL Front End Test Stand.
29. Beam Diagnostics for the Front End Test Stand at RAL [645 kB]
Proceedings of DIPAC 2007, May 2007
The Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL) is intended to demonstrate the early stages of acceleration (0-3MeV) and beam chopping required for high power proton particle accelerators, including proton drivers for http://scitation.aip.org/dbt/dbt.jsp?KEY=APCPCS&Volume=925&Issue=1pulsed neutron spallation sources and neutrino factories. The FETS ion source is required to produce a 60 mA beam in pulses up to 2ms long at up to 50 pps with an RMS emittance of 0.3 p mm mrad. A number of different diagnostic systems are currently under development to provide precise measurements of the H- ion beam. A pepperpot emittance measurement system, which is also capable of high resolution transverse beam density measurements, has been designed for use on the ISIS ion source development rig. This system is capable of sub-microsecond time-resolved measurements at a range of positions along the beam axis. Details are given of the improvements to the current design, including extensive tests on suitable scintillators and emittance and profile measurements are presented. Additionally, the designs of two different novel laser diagnostic systems for FETS are also presented.
28. The Development of the ISIS H- Surface Plasma Ion Source at RAL [236 kB]
18th Meeting of the International Collaboration on Advanced Neutron Sources, April 25-29, 2007
ISIS H- Penning Surface Plasma Source (SPS) has been a world leading operational H- ion source for 20 years; it routinely produces 35 mA of H- ions during a 200 us pulse at 50 Hz for uninterrupted periods of up to 50 days. This paper details the development of the source that has occurred over the last 5 years. The pulse length has been increased from 200 �s to 1.5 ms and the output current doubled to 70 mA. These developments are required for the new Front End Test Stand (FETS) currently being built at RAL. Extensive three dimensional finite element modeling has allowed the thermal operation of the source to be understood in detail: the temperatures around the discharge region have been calculated and the transient thermal behavior of the pulsed source studied. This has allowed the source duty cycle to be significantly increased.Electromagnetic finite element analysis has allowed the source extraction and beam transport to be investigated. Different extraction geometries have been designed and successfully tested to give higher output currents. An energy analyzer and two emittance measurement systems (slit-slit and pepperpot) have been developed to allow the beam to be fully characterized. Several geometry and infrastructure modifications have been implemented and will be discussed.
27. The ISIS Penning H− SPS and Diagnostic Developments at RAL [236 kB]
AIP Conf. Proc. Volume 925, pp. 71-78
11th International Symposium on the Production and Neutralization of Negative Ions and Beams August 10, 2007
This paper covers the recent work carried out at the Rutherford Appleton Laboratory (RAL) on the ISIS Ion Source Development Rig (ISDR). The development of a retarding potential energy analyzer is described and a measured energy spread of 17.6 eV � 1.5 eV from the ion source is reported. Variation in energy spread versus discharge current is shown. The development of a pepperpot emittance scanner to study emittance variation along the beam axis is discussed.
26. Particle Dynamics Calculations and Emittance Measurements at the FETS [1334 kB]
Proceedings of LINAC06, August 2006
High power proton particle accelerators in the MW range have many applications including drivers for spallation neutron sources, neutrino factories, transmuters (for transmuting long-lived nuclear waste products) and energy amplifiers. In order to contribute to the development of HPPAs, to prepare the way for an ISIS upgrade and to contribute to the UK design effort on neutrino factories, a front end test stand (FETS) is being constructed at the Rutherford Appleton Laboratory (RAL) in the UK. The aim of the FETS is to demonstrate the production of a 60 mA, 2 ms, 50 pps chopped beam at 3 MeV with sufficient beam quality. An overview on the status of the project together with the results of numerical simulations of the particle dynamics from the ion source to the RFQ exit will be presented. The particle distributions gained from the particle dynamics simulations will be compared with recent measurements of the transversal beam emittance behind the ion source and the results discussed.
25. Development of Emittance Scanner Software for ISIS [242 kB]
Proceedings of EPAC06, June 2006
Horizontal and vertical Faraday cup and slit scanners are used on ISIS, the 800MeV pulsed neutron source at the Rutherford Appleton Laboratory, to calculate the emittance of the beam. Software has been written in C++ to control the scanners, acquire and display beam data and compute an emittance value for the beam. The software allows the user more control, and has the ability to scan over a wider range, than was previously available.
24. LEBT Simulations and Ion Source Beam Measurements for the Front End Test Stand (FETS) [371 kB]
Proceedings of EPAC06, June 2006
The Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL) is intended to demonstrate the early stages of acceleration (0-3MeV) and beam chopping required for high power proton particle accelerators, including proton drivers for pulsed neutron spallation sources and neutrino factories. Optimisation of the beam focussing within the Low Energy Beam Transport (LEBT) is necessary to minimise beam losses upon acceleration within the FETS RadioFrequency Quadrupole (RFQ). Simulations of the LEBT are currently under way using the General Particle Tracer package (GPT). Previous envelope calculations suggest weak and strong focussing solutions for the LEBT solenoids. Definitive beam dynamics simulations in GPT require further measurements of the transverse emittances and beam profile of the ion source beam, due to the sensitivity of the simulations on the initial beam profile and level of space charge compensation. A pepperpot emittance/profile measurement system has been designed for use on the ISIS ion source development rig. Results from this pepperpot system are used to constrain the initial conditions for the GPT simulations.
23. Energy Distribution of H- Ions from the ISIS Ion Source [170 kB]
Proceedings of EPAC06, June 2006
We have used a specially designed retarding field energy analyzer with a resolution (? E /E) of approximately 2 x 10 -4 in order to measure the energy distribution, under different operating conditions, of the H- beam of the ISIS ion source. The paper presents the details of the analyzer and the first results obtained on the Ion Source Test Facility at RAL.
22. ISIS Upgrades - A Status Report [186kB]
Proceedings of EPAC06, June 2006
Since 2002 several particle accelerator upgrades have been made to the ISIS spallation neutron source at the Rutherford Appleton Laboratory in the UK, and upgrades are currently continuing in the form of the Second Target Station Project. The paper reviews the following programmes: a new extraction straight, replacement of the Cockcroft-Walton by an RFQ, installation of a second harmonic RF system, replacement and upgrading of ageing installed equipment, design and installation of improved diagnostics in conjunction with beam dynamics simulations, the Second Target Station Project, design and construction of a front end test stand, and the MICE programme. The paper also looks forward to possible future schemes at ISIS beyond the Second Target Station Project.
21. The RAL Front End Test Stand [135 kB]
Proceedings of EPAC06, June 2006
High power proton accelerators (HPPAs) with beam powers in the megawatt range have many possible applications including drivers for spallation neutron sources, neutrino factories, waste transmuters and tritium production facilities. These applications typically propose beam powers of 5 MW or more compared to the highest beam power achieved from a pulsed proton accelerator in routine operation of 0.16 MW at ISIS. The UK's commitment to the development of the next generation of HPPAs is demonstrated by a test stand being constructed in collaboration between RAL, Imperial College London and the University of Warwick. The aim of the RAL Front End Test Stand is to demonstrate that chopped low energy beams of high quality can be produced and is intended to allow generic experiments exploring a variety of operational regimes. This paper describes the status of the RAL Front End Test Stand which consists of five main components: a 60 mA H- ion source, a low energy beam transport, a 324 MHz Radio Frequency Quadrupole (RFQ) accelerator, a high speed beam chopper and a comprehensive suite of diagnostics. The aim is to demonstrate production of a 60 mA, 2 ms, 50 pps, chopped H- beam at 3 MeV.
20. Practical Experience in Extending the Ion Source and Injection System H- Ion Source Duty Cycle [381 kB]
Review of Scientific Instruments Volume 77, Number 3, March 2006
The ion source and injection system H- Penning surface-plasma source is currently being developed on the ion source development rig at Rutherford Appleton Laboratory in order to meet the requirements for the next generation of high-power proton drivers for particle accelerators. Finite element modeling has been used previously to study the effect of increasing the duty cycle. The main requirement to allow increased duty cycles is improved cooling. By simply reducing the thickness of a sheet of mica to improve thermal conductance to the cooling system, duty cycles of 1.5 ms at 50 Hz can be achieved. Slight increase in hydrogen flow rate is required as the duty cycle is increased. As the duty cycle is increased the output current reduces, however, there is no change in beam emittance. The source cooling system is described and the heat flows within the source are discussed.
19. Progress at the RAL Front End Test Stand [471 kB]
Nuclear Physics B (Proc. Suppl.) 155 (2006) 309-311
The progress in the design of a proton driver front end test stand at the Rutherford Appleton Laboratory (RAL) in the UK is presented. The aim of the test stand is to demonstrate the availability of well chopped H- beams suitable for future high power proton accelerators.
18. Separating the Penning and Analysing Fields in the ISIS H- Ion Source [281 kB]
Proceedings of PAC05, May 2005
The development of H- ion sources with performances exceeding those achieved today is a key requirement for the next generation of high power proton particle accelerators. The ion source development program at ISIS is now well established. To allow different ion source designs to be fully tested, the ability to vary the Penning field is required. Until now the Penning field has been generated by the same magnetic circuit that creates the analyzing field, giving no practical way of altering the Penning field alone. This paper describes the infrastructure changes required to allow the Penning field to be independently varied. The effect the Penning field has on beam current, emittance and discharge stability are discussed.
17. Testing, Installation, Commissioning and First Operation of the ISIS RFQ Pre-Injector Upgrade [453 kB]
Proceedings of PAC05, May 2005
Situated at the Rutherford Appleton Laboratory (Oxon., UK), ISIS is currently the world's most intense pulsed spallation neutron source, delivering 160 kW of 800 MeV protons to a tungsten target at 50 Hz. A major facility upgrade programme involves the construction of a second, 10 Hz target and an increase in the total beam power of up to 50% (i.e. up to 240 kW). To achieve the planned increase in average beam current to 300 �A whilst maintaining the current manageable levels of beam loss, four 2nd harmonic RF cavities have been installed in the synchrotron and the ageing Cockcroft-Walton preinjector in the linac has been replaced with a 665 keV, 202.5 MHz, 4-rod Radio Frequency Quadrupole (RFQ). This paper describes the extensive testing, installation, commissioning and successful initial operation of the RFQ pre-injector upgrade.
16. Magnet Design for the ISIS Second Target Station Proton Beam Line [144 kB]
Proceedings of PAC05, May 2005
The ISIS facility, based at the Rutherford Appleton Laboratory in the UK, is an intense source of neutrons and muons for condensed matter research. The particle accelerator facility delivers an 800 MeV proton beam of 2.5x1013 protons per pulse at 50 Hz to the present target station. As part of a facility upgrade, it is planned to share the source with a second, 10 Hz, target station. The beam line supplying this target will extract from the existing target station beam line. Electromagnetic Finite Element Modelling techniques have been used to design the magnets required to meet the specified beam line optics. Kicker, septum, dipole, quadrupole, and steering magnets are covered. The magnet design process, involving 2D and 3D modelling, the calculation of ideal shims and chamfers, choice of steel, design of conducting coils, handling of heating issues and eddy current effects, is discussed.
15. The RAL Front End Test Stand [115kB]
Nuclear Physics B (Proc. Suppl.) 149 (2005) 323-325
A design for a proton driver front end test stand at the Rutherford Appleton Laboratory (RAL) in the UK is presented. The aim is to demonstrate the availability of well chopped H- beams suitable for future high power proton accelerators for particle accelerators. Advantage is being taken of existing RAL R&D programmes on H- ion sources and beam choppers, and also of a previous RFQ test stand project at RAL for testing a new preinjector RFQ for the ISIS spallation neutron source.
14. Advances in the Ion Source Research and Development Program at ISIS [617kB]
AIP Conference Proceedings; Journal Volume: 763; Journal Issue: 1
10th International Symposium on Production and Neutralization of Negative Ions and Beams, Kiev (Ukraine), 14-17 Sep 2004
This paper covers the advances in the ion source research and development Program at ISIS over the last 2 years. The work is a combination of theoretical finite element analysis calculations and experiments conducted on a purpose built development rig. The broad development goals are higher beam current with longer pulse length. A Finite Element Analysis (FEA) model is used here to understand the steady state and dynamic thermal behavior of the source, and to investigate the design changes necessary to offset the extra heating. Electromagnetic FEA modeling of the extraction region of the ISIS H- ion source has suggested that the present set up of extraction electrode and 90�� sector magnet is sub-optimal, with the result that the beam profile is asymmetric, the beam is strongly divergent in the horizontal plane and there is severe aberration in the focusing in the vertical plane. The FEA model of the beam optics has demonstrated that relatively simple changes to the system should produce a dramatic improvement in performance. The theoretical and experimental results are compared here.
13. The Effect of Extraction Geometry on the Measured ISIS H Minus Ion Source Beam [624 kB]
Proceedings of EPAC04, July 2004
The ISIS H- ion source is currently being developed on the Ion Source Development Rig (ISDR) at Rutherford Appleton Laboratory (RAL) in order to meet the requirements for the next generation of high power proton drivers for particle accelerators. Recent Finite Element Analysis (FEA) electromagnetic modelling of the extraction region of the ISIS H- ion source has suggested that the present set up of extraction electrode and 90� sector magnet is sub-optimal, with the result that the beam profile is asymmetric, the beam is strongly divergent in the horizontal plane and there is severe aberration in the focusing in the vertical plane. The FEA model of the beam optics has demonstrated that relatively simple changes to the system should produce a dramatic improvement in performance. These changes have been incorporated on the Ion Source Development Rig (ISDR) at Rutherford Appleton Laboratory (RAL), and their effects on the H- beam are presented here.
12. Extending the Duty Cycle of the ISIS H Minus Ion Source, Thermal Considerations [304 kB]
Proceedings of EPAC04, July 2004
The ISIS H- ion source is currently being developed on the Ion Source Development Rig (ISDR) at Rutherford Appleton Laboratory (RAL) in order to meet the requirements for the next generation of high power proton drivers for particle accelerators. One key development goal is to increase the pulse width and duty cycle, but this has a significant effect on ion source temperatures if no other changes are made. A Finite Element Analysis (FEA) model has been produced previously [1] and is used here to understand the steady state and dynamic thermal behavior of the source, and to investigate the design changes necessary to offset the extra heating.
11. Thermal Modeling of the ISIS H- Ion Source [341 kB]
Review of Scientific Instruments Volume 75, Number 5, May 2004
The development of H2 ion sources with performances exceeding those achieved today is a key requirement for the next generation of high power proton accelerators. The ISIS Penning surface plasma source, which routinely produces 35 mA of H2 ions during a 200 ms pulse at 50 Hz for uninterrupted periods of up to 50 days, is regarded as one of the leading operational sources in the world, and should provide an excellent starting point for a development program. One goal is to produce pulse widths of 1.2 ms at 50 Hz and 2.5 ms at 50/3 Hz, thereby increasing the duty factor from 1% to as much as 10%. Increasing pulse widths will necessitate an improved cooling system to offset increased heating. The most effective cooling strategy will be determined by thermal finite element analysis of the ISIS ion source. The modeling will then be extended to find an optimal means of offsetting increased heat loading, and will minimize the amount of engineering required to produce an effective solution. Modeling of the ISIS source has established the temperature profiles of the source components. At the specific locations where temperatures are measured in operation using thermocouples the model values match those seen in practice. Transient modeling has been used to provide temperature variations for the source during the 20 ms period of the 50 Hz cycle.
10. Electromagnetic Modeling of the Extraction Region of the ISIS H- Ion Source [494 kB]
Review of Scientific Instruments Volume 75, Number 5, May 2004
The ISIS Penning surface plasma ion source, which routinely produces 35 mA of H2 ions during a 200 ms pulse at 50 Hz for uninterrupted periods of up to 50 days, is regarded as one of the leading operational sources in the world. The ISIS ion source should provide an excellent starting point for a development program to produce H2 ion sources with performances exceeding those achieved today, which will be a key requirement for the next generation of high power proton particle accelerators. One goal is to produce 60 mA of H2 ions from the source without large departures from the optimum conditions for source lifetime or increased emittance. As the ISIS source operates in the space-charge limited mode it is predicted that an increase in extraction potential from 17 to 25 kV should be sufficient to achieve this, and a suitable pulsed power supply for the ion source extraction electrode has been manufactured. An understanding of how extract geometry changes affect beam transport is essential for operation at higher extraction potential. An examination has been undertaken of the electromagnetic fields in the extract electrode region using MAFIA finite element analysis software. The effects of changing the extraction potential, gap, and electrode geometry are described.
9. Calculations Based on Measurements of Charge Deposited by a Streamer on a PTFE Surface [126 kB]
Surface charge on an insulator�s surface is studied using 3-dimesional finite element modelling. The calculations are based on measurements of surface charge deposited by a streamer on a PTFE surface. The surface electric field strengths associated with uniform surface charge density distributions over a 1mm2 region are calculated for a range of different measured charge densities. The effect of reducing the area of the surface charge whilst keeping the total amount of charge in the region constant, is observed. The surface charge is then modelled with a Gaussian distribution of charge and compared to that of a uniform distribution. By assuming a maximum allowable surface electric field strength an estimation of actual charged path diameter is made.
8. Corona Propagation and Charge Deposition on a PTFE Surface [642 kB]
A description is given of some properties of the corona discharge when propagating over a cylindrical PTFE insulator surface placed along the axis of a rod-plane electrode arrangement. A scanning electrostatic probe has been used to measure the density of charge deposited on the surface; it is shown that the total of net deposited charge is small compared with the total charge injected into the gap. Velocity of propagation has been measured. Effects of preceding coronas on succeeding ones and the nature of deposited charge after breakdown are described. Discussion is given in terms of electron lifetimes and attachment and photoemission processes.
7. High Resolution Measurements of Surface Charge Densities on Insulator Surfaces [859 kB]
The uses and limitations of the electrostatic probe for the measurement of charge densities on insulating surfaces are discussed. A development of the technique is described in which two important limitations have together been overcome: (i) The effects on the probe signal of charges on all points of the surface have been taken into account by means of a matrix inversion procedure. (ii) A robotic control system has been developed which enables the probe to follow and scan a wide range of axi-symmetric insulator profiles. The degree of resolution achieved enables the probe system to display and measure charge densities in individual streamer channels of a corona discharge on a PTFE surface. An example is given and comparison made with a dust figure of the same event.
6. Surface Charge Density and its Influence on Insulator Flashover - PhD Thesis [12246 kB]
A technique is developed to measure high-resolution surface charge density distributions on high voltage insulators. This technique is developed into a piece of laboratory equipment and used to investigate the surface charging of practical axi-symmetric insulators by high voltage discharges and its influence on insulator flashover. The different techniques available for surface charge measurement are discussed and the electrostatic probe is chosen for development. The process of calculating surface charge density distributions from probe voltage measurements is detailed. The probe and the mechanism designed to move it over a range of different sized and contoured axi-symmetric insulators is detailed. The software that automates the entire technique is then described. The Software controls the actual measurement process; calculates the charge density distributions; and allows the user to view and analyse the results. The measurement system is evaluated and tested thoroughly and then used for a series of experiments. The experimental work is based around cylindrical PTFE insulators positioned in a rod-plane gap. Various techniques for neutralising surface charge are evaluated. An impulse generator is used to produce single positive discharge events in the rod-plane gap. Each discharge event is recorded using three photomultipliers and current shunts discharge current measurements. Charge density distributions are also recorded. Three different rod diameters and rod surface separations are investigated. The effect of flashover on surface charge is studied and the charge distributions left by negative impulse, DC and AC test voltages on the rod are recorded. The surface charging of several other materials is then briefly studied along with the decay of surface charge and the surface charging of a contoured insulator with a single shed. A full analysis using three-dimensional finite modelling is undertaken of the electrostatic probe, the electrode arrangement, and of the field produced by surface charge.
5. Simulation of an Early Streamer Emission Air Terminal for Application to Lightning Protection [333 kB]
The ESE concept represents an attempt to improve the zone of protection offered by a conventional Franklin rod air terminal. The premise on which ESE lightning protection relies is this: the earlier an air terminal is able to launch an upward leader, during the attachment phase of a lightning discharge, the larger the zone of protection offered by that air terminal. In this paper, the authors have adopted a methodical approach for examining, under laboratory conditions, the extent to which the discharge emanating from an air terminal can be influenced by voltage application to the tip of the air terminal-since such voltage application is one technique employed by ESE air terminals to expedite upward leader inception relative to a Franklin rod. The experimental method used and the preliminary observations of the study are reported here.
This paper describes the method of operation of a system for measuring high-resolution surface charge density maps on practical insulator specimens using an electrostatic probe. Apparatus is described that can scan the electrostatic probe over the surface of the insulator and record the probe signal. The process of obtaining a charge density map from the probe signal measurements is explained. An example charge distribution is shown.
3. Tests of the `Early Streamer Emission' Principle for Protection Against Lightning [784 kB]
Experiments are described which are designed to test two devices based on the `early streamer emission' (ESE) principle, for lightning protection, against the traditional Franklin rod. In all three cases, the device was subjected to a steady negative electric field from a sphere, simulating the field beneath a thundercloud, prior to application of a superimposed negative impulse field, simulating the field due to the downward leader. The first device consisted of a vertical rod to which a subsidiary 1/50 �s positive impulse voltage, variable up to 40 kV peak, could be applied with varying delays from the start of the negative impulse field. Energising of the rod was thus independent of the applied negative field. The second device was a commercial product, energising of which was controlled by its own power supply. Sparkover voltages in the sphere/device gaps and times to breakdown were measured. It is shown that the ESE devices showed a small advantage, in time to breakdown, over the Franklin rod.
2. Some Factors Relating to the Early Streamer Emission Principle [472kB]
A brief review is given of the means by which additional ionisation has been introduced at the tip of a lightning conductor final, with a view to increasing the probability of attachment to a downward leader. Attention is concentrated, in present work, on the "early streamer emission" principle, in which corona is initiated by either a steady or pulsed high voltage applied to a finial. The field of an approaching downward leader is simulated, in these experiments, by application of a negative impulse voltage to a sphere, located above the finial. It is shown that a steady corona does not improve the finial performance, under the conditions used, and that a pulsed corona must be applied within a critical time range, in order to be effective. The implications for lightning protection are briefly examined.
1. Lightning Protection of Buildings Using Active Finials - MSc Dissertation [727 kB]
UMIST Manchester September 1996
This dissertation investigates the efficacy of active lightning finials. The active lightning protection method studied involves the application of a voltage to the finial. An active finial working on this principle is simulated experimentally. The field experienced by a lighting finial during a lightning strike is analysed and simulated to allow investigation of the artificial active device in the laboratory.
