Publications
137 results found
Nonnenmacher T, Dascalu T-S, Bingham R, et al., 2021, Anomalous beam transport through Gabor (plasma) lens prototype, Applied Sciences-Basel, Vol: 11, Pages: 1-17, ISSN: 2076-3417
An electron plasma lens is a cost-effective, compact, strong-focusing element that can ensure efficient capture of low-energy proton and ion beams from laser-driven sources. A Gabor lens prototype was built for high electron density operation at Imperial College London. The parameters of the stable operation regime of the lens and its performance during a beam test with 1.4 MeV protons are reported here. Narrow pencil beams were imaged on a scintillator screen 67 cm downstream of the lens. The lens converted the pencil beams into rings that show position-dependent shape and intensity modulation that are dependent on the settings of the lens. Characterisation of the focusing effect suggests that the plasma column exhibited an off-axis rotation similar to the m=1 diocotron instability. The association of the instability with the cause of the rings was investigated using particle tracking simulations.
Aymar G, Becker T, Boogert S, et al., 2020, LhARA: The Laser-hybrid accelerator for radiobiological applications, Frontiers in Physics, Vol: 8, Pages: 1-21, ISSN: 2296-424X
The “Laser-hybrid Accelerator for Radiobiological Applications,” LhARA, is conceived as a novel, flexible facility dedicated to the study of radiobiology. The technologies demonstrated in LhARA, which have wide application, will be developed to allow particle-beam therapy to be delivered in a new regimen, combining a variety of ion species in a single treatment fraction and exploiting ultra-high dose rates. LhARA will be a hybrid accelerator system in which laser interactions drive the creation of a large flux of protons or light ions that are captured using a plasma (Gabor) lens and formed into a beam. The laser-driven source allows protons and ions to be captured at energies significantly above those that pertain in conventional facilities, thus evading the current space-charge limit on the instantaneous dose rate that can be delivered. The laser-hybrid approach, therefore, will allow the radiobiology that determines the response of tissue to ionizing radiation to be studied with protons and light ions using a wide variety of time structures, spectral distributions, and spatial configurations at instantaneous dose rates up to and significantly beyond the ultra-high dose-rate “FLASH” regime. It is proposed that LhARA be developed in two stages. In the first stage, a programme of in vitro radiobiology will be served with proton beams with energies between 10 and 15 MeV. In stage two, the beam will be accelerated using a fixed-field alternating-gradient accelerator (FFA). This will allow experiments to be carried out in vitro and in vivo with proton beam energies of up to 127 MeV. In addition, ion beams with energies up to 33.4 MeV per nucleon will be available for in vitro and in vivo experiments. This paper presents the conceptual design for LhARA and the R&D programme by which the LhARA consortium seeks to establish the facility.
Aymar G, Becker T, Boogert S, et al., 2020, The laser-hybrid accelerator for radiobiological applications, Publisher: arXiv
The `Laser-hybrid Accelerator for Radiobiological Applications', LhARA, isconceived as a novel, uniquely-flexible facility dedicated to the study ofradiobiology. The technologies demonstrated in LhARA, which have wideapplication, will be developed to allow particle-beam therapy to be deliveredin a completely new regime, combining a variety of ion species in a singletreatment fraction and exploiting ultra-high dose rates. LhARA will be a hybridaccelerator system in which laser interactions drive the creation of a largeflux of protons or light ions that are captured using a plasma (Gabor) lens andformed into a beam. The laser-driven source allows protons and ions to becaptured at energies significantly above those that pertain in conventionalfacilities, thus evading the current space-charge limit on the instantaneousdose rate that can be delivered. The laser-hybrid approach, therefore, willallow the vast ``terra incognita'' of the radiobiology that determines theresponse of tissue to ionising radiation to be studied with protons and lightions using a wide variety of time structures, spectral distributions, andspatial configurations at instantaneous dose rates up to and significantlybeyond the ultra-high dose-rate `FLASH' regime. It is proposed that LhARA be developed in two stages. In the first stage, aprogramme of in vitro radiobiology will be served with proton beams withenergies between 10MeV and 15MeV. In stage two, the beam will be acceleratedusing a fixed-field accelerator (FFA). This will allow experiments to becarried out in vitro and in vivo with proton beam energies of up to 127MeV. Inaddition, ion beams with energies up to 33.4MeV per nucleon will be availablefor in vitro and in vivo experiments. This paper presents the conceptual designfor LhARA and the R&D programme by which the LhARA consortium seeks toestablish the facility.
Kurup A, Pasternak J, Taylor R, et al., 2019, Simulation of a radiobiology facility for the Centre for the Clinical Application of Particles, Physica Medica, Vol: 65, Pages: 21-28, ISSN: 1120-1797
The Centre for the Clinical Application of Particles’ Laser-hybrid Accelerator for Radiobiological Applications (LhARA) facility is being studied and requires simulation of novel accelerator components (such as the Gabor lens capture system), detector simulation and simulation of the ion beam interaction with cells. The first stage of LhARA will provide protons up to 15 MeV for in vitro studies. The second stage of LhARA will use a fixed-field accelerator to increase the energy of the particles to allow in vivo studies with protons and in vitro studies with heavier ions.BDSIM, a Geant4 based accelerator simulation tool, has been used to perform particle tracking simulations to verify the beam optics design done by BeamOptics and these show good agreement. Design parameters were defined based on an EPOCH simulation of the laser source and a series of mono-energetic input beams were generated from this by BDSIM. The tracking results show the large angular spread of the input beam (0.2 rad) can be transported with a transmission of almost 100% whilst keeping divergence at the end station very low (<0.1 mrad). The legacy of LhARA will be the demonstration of technologies that could drive a step-change in the provision of proton and light ion therapy (i.e. a laser source coupled to a Gabor lens capture and a fixed-field accelerator), and a system capable of delivering a comprehensive set of experimental data that can be used to enhance the clinical application of proton and light ion therapy.
Gibson SM, Alden SE, Bosco A, et al., 2018, A novel longitudinal laserwire to non-invasively measure 6-dimensional bunch parameters at high current hydrogen ion accelerators, 9th International Particle Accelerator Conference, IPAC18, ISSN: 1742-6588
© Published under licence by IOP Publishing Ltd. Optical methods for non-invasive beam diagnostics of high current H- ion accelerators have been developed in recent years. Such laserwires typically measure a 1D beam profile and/or 2D transverse emittance from the products of photo-detached ions as a laser beam is scanned across the H- beam. For laser pulse durations (∼80 ns) longer than the RF period (∼3ns), the detector integrates many complete bunches, enabling only transverse beam monitoring. This paper presents a new technique to capture a series of time resolved transverse emittance measurements along the bunch train. A fast (∼10 ps) pulsed laser photo-detaches ions within each bunch and is synchronised to sample consecutive bunches at certain longitudinal positions along each bunch. A fast detector records the spatial distribution and time-of-flight of the neutralised H0, thus both the transverse and longitudinal emittance are reconstructed. We present simulations of a time varying pulsed laser field interacting within an H- bunch, and estimate the yield, spatial and time distributions of H0 arriving at the detector. We summarise the design of a recently funded longitudinal laserwire being installed in FETS at RAL, UK.
Promdee W, Edgecock TR, Boorman G, et al., 2017, Bead pull measurements of the FETS RFQ at RAL, Pages: 4349-4351
A Radio Frequency Quadrupole (RFQ) is a part of the Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL), Didcot, UK. The aim of the FETS project is to produce a 60 mA H-beam at 3 MeV. The RFQ is a four-vane type with 4 modules, each of 1 m length, and is designed to accelerate the beam from 65 keV to 3 MeV at 324 MHz. A bead pull system has been designed to measure the field along the RFQ. This will be used in conjunction with 64 tuners to produce a uniform field. In order to optimise the tuning procedure, a model of the RFQ has been created in COMSOL Multiphysics. This study shows the results from the bead pull measurements and the tuning studies.
Edgecock TR, Caretta O, Davenne T, et al., 2016, Publisher’s Note: High intensity neutrino oscillation facilities in Europe [Phys. Rev. Accel. Beams 16, 021002 (2013)], Physical Review Accelerators and Beams, Vol: 19, ISSN: 2469-9888
Posocco PA, Pozimski JR, Xia Y, et al., 2016, First Test of The Imperial College Gabor (Plasma) Lens prototype at the Surrey Ion Beam centre, 7th International Particle Accelerator Conference (IPAC 2016), Publisher: Joint Accelerator Conferences, Pages: 1598-1600
The first plasma (Gabor) lens prototype operating at high electron density was built by the Imperial College London in 2015. In November 2015 the lens was tested at the Ion Beam Centre of the University of Surrey with a 1 MeV proton beam. Over 500 snapshots of the beam hitting a scintillator screen installed 0.5 m downstream of the lens were taken for a wide range of settings. Unexpectedly, instead of over- or underfocusing the incoming particles, the lens converted pencil beams into rings. In addition to the dependence of their radius on the lens settings, periodic features appeared along the circumference, suggesting that the electron plasma was exited into a coherent off-axis rotation. The cause of this phenomenon is under investigation.
Pozimski JR, Aslaninejad M, Posocco PA, 2016, Advanced Gabor Lens Lattice for Laser Driven Hadron Therapy and Other Applications, 7th International Particle Accelerator Conference (IPAC 2016), Publisher: Joint Accelerator Conferences, Pages: 1595-1597
The application of laser accelerated ion beams in hadron therapy requires a beam optics with unique features. Due to the spectral and spatial distribution of laser accelerated protons a compact ion optical system with therapy applications, based on Gabor space charge lenses for collecting, focusing and energy filtering the laser produced proton beam, has significant advantages compared with other setups. While a passive momentum selection could improve already the usability of laser driven hadron, we show that an advanced lattice utilizing additional RF cavities not only will deliver a momentum spread smaller than conventional accelerators, but also will increases the dose delivered. Furthermore, a possible near term application in the field of radio nuclide production is presented.
Posocco PA, Pozimski JK, Merchant MJ, et al., 2016, FIRST TEST OF THE IMPERIAL COLLEGE GABOR (PLASMA) LENS PROTOTYPE AT THE SURREY ION BEAM CENTRE, IPAC16
Caldwell A, Adli E, Amorim L, et al., 2016, Path to AWAKE: Evolution of the concept, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol: 829, Pages: 3-16, ISSN: 0168-9002
This paper describes the conceptual steps in reaching the design of the AWAKE experiment currently under construction at CERN. We start with an introduction to plasma wakefield acceleration and the motivation for using proton drivers. We then describe the self-modulation instability - a key to an early realization of the concept. This is then followed by the historical development of the experimental design, where the critical issues that arose and their solutions are described. We conclude with the design of the experiment as it is being realized at CERN and some words on the future outlook. A summary of the AWAKE design and construction status as presented in this conference is given in Gschwendtner et al. [1].
Hofmann T, Kruchinin KO, Bosco A, et al., 2015, Demonstration of a laserwire emittance scanner for hydrogen ion beams at CERN, Physical Review Special Topics-Accelerators and Beams, Vol: 18, ISSN: 1098-4402
A noninvasive, compact laserwire system has been developed to measure the transverse emittance of an H− beam and has been demonstrated at the new LINAC4 injector for the LHC at CERN. Light from a low power, pulsed laser source is conveyed via fiber to collide with the H− beam, a fraction of which is neutralized and then intercepted by a downstream diamond detector. Scanning the focused laser across the H− beam and measuring the distribution of the photo-neutralized particles enables the transverse emittance to be reconstructed. The vertical phase-space distribution of a 3 MeV beam during LINAC4 commissioning has been measured by the laserwire and verified with a conventional slit and grid method.
Alsari S, Aslaninejad M, Pozimski J, 2015, Use of phase information with a stepper motor to control frequency for tuning system of the Front End Test Stand Radio Frequency Quadrupole at Rutherford Appleton Laboratory, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, Vol: 775, Pages: 105-111, ISSN: 0168-9002
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Kurup A, Pozimski J, Savage P, et al., 2015, Simulations of the FETS laser diagnostic, Pages: 521-525
The Front-End Test Stand (FETS) aims to demonstrate clean chopping of a 60mA, 3MeV H- ion beam. Such high beam intensities require unconventional emittance and profile measuring devices such as the laserwire system that will be used on FETS. A laser is used to neutralise part of the H- ion beam. The main beam is then separated from the stripped beam by using a dipole magnet. This paper presents tracking results of the laser diagnostic lattice using a simulated field map of an existing dipole magnet and investigates the possibility of laser stripping upstream of the dipole.
Boorman G, Gibson SM, Rajaeifar N, et al., 2015, Characterising the signal processing system for beam position monitors at the front end test stand, Pages: 526-529
A number of beam position monitors (BPM) are being installed at the Front End Test Stand (FETS) H– ion source at the Rutherford Appleton Laboratory, UK, as part of the 3 MeV medium energy beam transport. The FETS ion source delivers pulses up to 2 ms long at a rate up to 50 Hz and a maximum current of 60 mA, with a 324 MHz micro-bunch structure imposed by the frequency of the FETS RF acceleration cavity. The response of an in-house designed button BPM has been simulated and then characterised on a wire-based test-rig and the results are presented. The output from a custom algorithm running on a commercial PXI-based FPGA signal processing system is evaluated using test signals from both a function generator and the BPM in the test-rig, to verify the speed and precision of the processing algorithm. The processing system can determine the beam position in eight BPMs, with a precision of better than 20 µm, within one microsecond of the signal sampling being completed.
Kruchinin KO, Boorman G, Bosco A, et al., 2015, Laserwire emittance scanner at CERN LINAC4, Pages: 1146-1149
Linac 4 presently under construction at CERN is designed to replace the existing 50 MeV Linac 2 in the LHC injector chain and will accelerate the beam of high current negative hydrogen ions to 160 MeV. During the commissioning a laserwire emittance scanner has been installed allowing noninvasive measuring of the emittance at 3 MeV and 12 MeV setups. A relatively low power infrared fibre coupled laser w a s focused in the interaction region down to ∼150 μm and collided with the ion beam neutralising negative ions. A t each transverse laser position with respect to the ion beam the angular distribution of the neutral particle beamlets w a s recorded b y scanning a diamond detector across the beamlet at a certain distance from the interaction point while the main beam of the H- ions w a s deflected using the dipole magnet installed upstream the detector. Measuring the profile of the beamlet b y scanning the laser across the beam allows to directly measure the transverse phase-space distribution and reconstruct the transverse beam emittance. In this report w e will describe the analysis of the data collected during the 3 MeV and 12 MeV operation of the Linac 4. W e will discuss the hardware status and future plans.
Bogomilov M, Matev R, Tsenov R, et al., 2014, Neutrino factory, PHYSICAL REVIEW SPECIAL TOPICS-ACCELERATORS AND BEAMS, Vol: 17, ISSN: 1098-4402
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Aslaninejad M, Pozimski J, Savage P, et al., 2014, Lattice and component design for the front end test stand MEBT at RAL, Pages: 1205-1207
The Front End Test Stand (FETS) linear accelerator at Rutherford Appleton Laboratory (RAL) will accelerate a 60 mA, 2 ms, 50 pps H- beam to 3MeV energy. The aim of FETS is to demonstrate perfect chopping using a novel 2 stage (fast / slow) chopper scheme. The beam chopper and associated beam dumps are located in the MEBT. Achieving a low emittance-growth under the influence of strong, non-linear space-charge forces in a lattice which has to accommodate the long chopping elements is challenging. The baseline FETS MEBT design is 4.3 m long and contains 7 quadrupoles, 3 rebunching cavities, a fast and slow chopper deflector and two beam dumps. In particle dynamics simulations using a distribution from an RFQ simulation as an input, beam loss for the un-chopped beam is below 1% while the chopping efficiency is >99 % in both choppers. The final MEBT lattice chosen for FETS will be presented together with particle tracking results and design details of the beam line components.
Kruchinin KO, Bosco A, Gibson SM, et al., 2014, Simulation results of the FETS laserwire emittance scanner, Pages: 3729-3731
The Front EndTest 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. Atsuch 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. W e 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.
Gibson SM, Boorman G, Bosco A, et al., 2014, A fibre coupled, low power laserwire emittance scanner at CERN LINAC4, Pages: 3725-3728
The new LINAC4 will accelerate H- ions to 160 MeV and ultimately replace the existing 50 MeV LINAC2 in the injector chain for the LHC upgrade. During commissioning in 2013, a laserwire scanner and diamond strip detector were installed for non-invasive emittance measurements of the 3MeV H- beam. Synergy with the 3MeV H- Front End Test Stand at RAL, has stimulated collaborative development of a novel laserwire system. A low peak power (8 kW) pulsed laser is fibre-coupled for remote installation and alignment free operation. Motorized focusing optics enable remote control of the thickness and position of the laserwire delivered to the vacuum chamber, in which the laser light neutralises a small fraction of H- ions. Unde-flected by a dipole magnet, these H atoms drift downstream, where their spatial profile is recorded by a highly sensitive diamond strip detector with ns-time resolution. We present first tests of the laserwire emittance scanner, including measurements of the photo detachment signal with respect to the background from residual gas interactions. The first laserwire transverse beam profile and emittance measurements are compared with conventional slit-grid diagnostics.
Alsari S, Pozimski JK, Savage P, et al., 2014, RF delivery system for fets, Pages: 3902-3904
The Front End Test Stand (FETS) is an experiment based at the Rutherford Appleton Laboratory (RAL) in the UK. In this experiment, the first stages necessary to produce a very high quality, chopped H-ion beam as required for the next generation of high power proton accelerators (HPPAs) are designed, built and tested. HPPAs with beam powers in the megawatt range have many possible applications including drivers for spallation neutron sources, neutrino factories, accelerator driven sub-critical systems, waste transmuters and tritium production facilities. An RF system outline, RF circulator installation, RFQ frequency test, and Buncher RF amplifiers test are presented and discussed. Experimental measurements of the RFQ frequency for the first metre of the 4-metre RFQ and chopping cavities' RF power amplifiers operating will be presented as part of the system testing results.
Back J, Faircloth D, Gabor C, et al., 2014, Performance of the low energy beam transport at the RAL front end test stand, Pages: 3406-3408
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 protondrivers 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.
Jolly S, Easton M, Lawrie S, et al., 2014, Novel integrated design framework for radio frequency quadrupoles, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, Vol: 735, Pages: 240-259, ISSN: 0168-9002
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Savage P, Aslaninejad M, Pozimski J, et al., 2013, Production of the fets RFQ, IPAC 2013: Proceedings of the 4th International Particle Accelerator Conference, Pages: 3726-3728
The Front End Test Stand (FETS) project at RAL will use a 324 MHz 4-vane Radio Frequency Quadrupole (RFQ) to accelerate H- ions from 65keV to 3 MeV. This paper will report on the current status of the production of the FETS RFQ and will detail the manufacturing strategy used to produce the major and minor vanes. In addition the inspection results will be shown and the experiences from the assembly and alignment operations will be shared. Finally, the design of the bead-pull apparatus, end flanges, tuners and pick-ups required to measure the frequency and field-flatness of the assembled RFQ will be discussed.
Aslaninejad JM, Pozimski J, Savage P, 2013, Mebt design for the front end test stand project at RAL, IPAC 2013: Proceedings of the 4th International Particle Accelerator Conference, Pages: 3969-3971
The Front End Test Stand (FETS) linear accelerator at the Rutherford Appleton laboratory (RAL) will accelerate a 60 mA, 2 ms, 50 pps H- beam to 3 MeV. A new lattice for the Medium Energy Beam Transport (MEBT) with a fast-slow chopping system is presented. The new lattice has more free space to position the diagnostics. Beam dynamic simulation, with the space charge effects included, has shown very good particle transmission in the new lattice.
Letchford A, Clarke-Gayther M, Faircloth D, et al., 2013, Status of the ral front end test stand, IPAC 2013: Proceedings of the 4th International Particle Accelerator Conference, Pages: 3963-3965
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.
Jolly S, D'arcy R, Pozimski J, et al., 2013, Acceptance and transmission simulations of the fets RFQ, IPAC 2013: Proceedings of the 4th International Particle Accelerator Conference, Pages: 3720-3722
A 4 m-long, 324MHz four-vane RFQ, consisting of four coupled sections, has been designed for the Front End Test Stand (FETS) at RAL in the UK. A novel design method, integrating the CAD and electromagnetic design of the RFQ with beam dynamics simulations, was used to optimise the design of the RFQ. With the design of the RFQ fixed, the focus has been on optimising the transmission of the RFQ at 3MeV and matching the output of the FETS Low Energy Beam Transport (LEBT) to the RFQ acceptance. Extensive simulations have been carried out using General Particle Tracer (GPT) to map out the acceptance of the FETS RFQ for a 65 keV H- input beam. Particular attention has focussed on optimising the simulations to match the optimised output of the FETS Penning-type H- ion source. Results are presented of the transverse phase space limits on the RFQ input acceptance in both the zero current and full space charge regimes.
Alsari S, Pozimski JK, Savage P, et al., 2013, FETS RF system design and circulator testing, IPAC 2013: Proceedings of the 4th International Particle Accelerator Conference, Pages: 2851-2853
The Front End Test Stand (FETS) is an experiment based at the Rutherford Appleton Laboratory (RAL) in the UK. In this experiment, the first stages necessary to produce a very high quality, chopped H- ion beam as required for the next generation of high power proton accelerators (HPPAs) are designed, built and tested. HPPAs with beam powers in the megawatt range have many possible applications including drivers for spallation neutron sources, neutrino factories, accelerator driven sub-critical systems, waste transmuters and tritium production facilities. An RF system outline and design options of the waveguide and coaxial parts with shielding are presented and discussed in this paper. Experimental measurements of the system's circulator low power test will be presented as part of the system testing results. Copyright © 2013 by JACoW- cc Creative Commons Attribution 3.0 (CC-BY-3.0).
Pozimski J, Savage P, Alsari S, et al., 2013, Investigation of space charge compensation at fets, IPAC 2013: Proceedings of the 4th International Particle Accelerator Conference, Pages: 3723-3725
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 sec could be concluded from measurements [2]. In this paper the results of further experimental work will be presented together with discussion of the findings.,.
Gibson SM, Boorman G, Bosco A, et al., 2013, Overview of laserwire beam profile and emittance measurements for high power proton accelerators, Pages: 531-534
Laserwires were originally developed to measure micron-sized electron beams via Compton scattering, where traditional wire scanners are at the limit of their resolution. Laserwires have since been applied to larger beam-size, high power H- ion beams, where the non-invasive method can probe beam densities that would damage traditional diagnostics. While photo-detachment of H- ions is now routine to measure beam profiles, extending the technique to transverse and longitudinal emittance measurements is a key aim of the laserwire emittance scanner under construction at the Front End Test Stand (FETS) at the RAL. A pulsed, 30 kHz, 8 kW peak power laser is fibre-coupled to motorized collimating optics, which controls the position and thickness of the laserwire delivered to the H-interaction chamber. The laserwire slices out a beamlet of neutralized particles, which propagate to a downstream scintillator and camera. The emittance is reconstructed from 2D images as the laserwire position is scanned. Results from the delivery optics, scintillator tests and particle tracking simulations of the full system are reviewed. Plans to deploy the FETS laser system at the LINAC4 at CERN are outlined.
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