IPAC2014 - List of Authors (Letchford, A.P.)

Paper	Title	Page
TUPRO072	Lattice and Component Design for the Front End Test Stand MEBT at RAL	1205
	M. Aslaninejad, J.K. Pozimski, P. Savage Imperial College of Science and Technology, Department of Physics, London, United Kingdom M.A. Clarke-Gayther, A.P. Letchford, D.C. Plostinar STFC/RAL, Chilton, Didcot, Oxon, United Kingdom S.R. Lawrie STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	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. 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 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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRO072
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THPME073	Performance of the Low Energy Beam Transport at the RAL Front End Test Stand	3406
	J.J. Back University of Warwick, Coventry, United Kingdom D.C. Faircloth, A.P. Letchford STFC/RAL, Chilton, Didcot, Oxon, United Kingdom C. Gabor STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom S.R. Lawrie STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom J.K. Pozimski Imperial College of Science and Technology, Department of Physics, London, United Kingdom
	The Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL) 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 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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPME073
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THPRI058	RF Delivery System for FETS	3902
	S.M.H. Alsari, M. Aslaninejad, J.K. Pozimski, P. Savage Imperial College of Science and Technology, Department of Physics, London, United Kingdom M. Dudman, A.P. Letchford STFC/RAL, Chilton, Didcot, Oxon, United Kingdom
	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, circulator high power tests, RF amplifiers tests, waveguide run with shielding and couplers design are presented and discussed in this paper. Experimental measurements of the system’s circulator and RF Amplifiers high power test will be presented as part of the system testing results.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI058
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MOPRI015	Installing the VESPA H⁻ Ion Source Test Stand at RAL	614
	S.R. Lawrie, D.C. Faircloth, A.P. Letchford, M. Perkins, M. Whitehead, T. Wood STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-MOPRI015
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THPME186	Development of a BPM System using a Commercial FPGA Card and Digitizer Adaptor Module for FETS	3716
	G.E. Boorman, S.M. Gibson Royal Holloway, University of London, Surrey, United Kingdom R.T.P. D'Arcy, S. Jolly UCL, London, United Kingdom S.R. Lawrie, A.P. Letchford STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	A series of beam position monitors (BPMs) will be installed at the Front End Test Stand (FETS) at RAL as part of the 3 MeV Medium Energy Beam Transport (MEBT). The BPMs analyse 2 ms long, 60 mA beam pulses delivered to the MEBT by a 324 MHz Radio Frequency Quadrupole (RFQ). Initial linearity and resolution measurements from the prototype button BPMs are shown. The development of the algorithm for the processing of the BPM signals using a commercial PXI-based FPGA card is discussed and initial measurements of the electronics and signal processing are presented. The test-rig used to characterise each BPM and further develop the processing algorithm is described. The position and phase are measured several times throughout the duration of each pulse, and the measurements are made available via an EPICS server.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPME186
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THPME190	A Fibre Coupled, Low Power Laserwire Emittance Scanner at CERN LINAC4	3725
	S.M. Gibson, G.E. Boorman, A. Bosco, K.O. Kruchinin Royal Holloway, University of London, Surrey, United Kingdom C. Gabor STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom T. Hofmann, F. Roncarolo CERN, Geneva, Switzerland A.P. Letchford STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom J.K. Pozimski, P. Savage Imperial College of Science and Technology, Department of Physics, London, United Kingdom
	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 3 MeV H⁻ beam. Synergy with the 3 MeV H⁻ Front End Test Stand at RAL, has stimulated collaborative development of a novel laserwire system. A low peak power (8kW) 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. Undeflected 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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPME190
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THPRI056	A New Debunching Cavity for the ISIS H⁻ Injector	3899
	B.S. Drumm, A.P. Letchford, R.E. Williamson STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom M. Keelan STFC/RAL, Chilton, Didcot, Oxon, United Kingdom
	The energy range of the ISIS 70MeV H⁻ injected beam is reduced using an RF debunching cavity. The existing cavity consists of a mild steel vacuum vessel containing a water-cooled copper shell into which RF power is fed. The unit is made up of components designed for the 50 MeV Proton Linear Accelerator (PLA) which used to occupy the Rutherford Appleton Laboratory (RAL) site between 1957 and 1969. The component drawings date back to the late 1960s. Due to its age, complexity and a lack of spares, there is a need for a modern solution. This paper documents the development of a new debunching cavity for the ISIS neutron source.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI056
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Lattice and Component Design for the Front End Test Stand MEBT at RAL

1205

M. Aslaninejad, J.K. Pozimski, P. Savage
Imperial College of Science and Technology, Department of Physics, London, United Kingdom
M.A. Clarke-Gayther, A.P. Letchford, D.C. Plostinar
STFC/RAL, Chilton, Didcot, Oxon, United Kingdom
S.R. Lawrie
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom

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. 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 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.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRO072

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPME073

Performance of the Low Energy Beam Transport at the RAL Front End Test Stand

3406

J.J. Back
University of Warwick, Coventry, United Kingdom
D.C. Faircloth, A.P. Letchford
STFC/RAL, Chilton, Didcot, Oxon, United Kingdom
C. Gabor
STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom
S.R. Lawrie
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
J.K. Pozimski
Imperial College of Science and Technology, Department of Physics, London, United Kingdom

The Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL) 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 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.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPME073

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPRI058

RF Delivery System for FETS

3902

S.M.H. Alsari, M. Aslaninejad, J.K. Pozimski, P. Savage
Imperial College of Science and Technology, Department of Physics, London, United Kingdom
M. Dudman, A.P. Letchford
STFC/RAL, Chilton, Didcot, Oxon, United Kingdom

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, circulator high power tests, RF amplifiers tests, waveguide run with shielding and couplers design are presented and discussed in this paper. Experimental measurements of the system’s circulator and RF Amplifiers high power test will be presented as part of the system testing results.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI058

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPRI015

Installing the VESPA H⁻ Ion Source Test Stand at RAL

614

S.R. Lawrie, D.C. Faircloth, A.P. Letchford, M. Perkins, M. Whitehead, T. Wood
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom

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.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-MOPRI015

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPME186

Development of a BPM System using a Commercial FPGA Card and Digitizer Adaptor Module for FETS

3716

G.E. Boorman, S.M. Gibson
Royal Holloway, University of London, Surrey, United Kingdom
R.T.P. D'Arcy, S. Jolly
UCL, London, United Kingdom
S.R. Lawrie, A.P. Letchford
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom

A series of beam position monitors (BPMs) will be installed at the Front End Test Stand (FETS) at RAL as part of the 3 MeV Medium Energy Beam Transport (MEBT). The BPMs analyse 2 ms long, 60 mA beam pulses delivered to the MEBT by a 324 MHz Radio Frequency Quadrupole (RFQ). Initial linearity and resolution measurements from the prototype button BPMs are shown. The development of the algorithm for the processing of the BPM signals using a commercial PXI-based FPGA card is discussed and initial measurements of the electronics and signal processing are presented. The test-rig used to characterise each BPM and further develop the processing algorithm is described. The position and phase are measured several times throughout the duration of each pulse, and the measurements are made available via an EPICS server.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPME186

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPME190

A Fibre Coupled, Low Power Laserwire Emittance Scanner at CERN LINAC4

3725

S.M. Gibson, G.E. Boorman, A. Bosco, K.O. Kruchinin
Royal Holloway, University of London, Surrey, United Kingdom
C. Gabor
STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom
T. Hofmann, F. Roncarolo
CERN, Geneva, Switzerland
A.P. Letchford
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
J.K. Pozimski, P. Savage
Imperial College of Science and Technology, Department of Physics, London, United Kingdom

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 3 MeV H⁻ beam. Synergy with the 3 MeV H⁻ Front End Test Stand at RAL, has stimulated collaborative development of a novel laserwire system. A low peak power (8kW) 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. Undeflected 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.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPME190

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPRI056

A New Debunching Cavity for the ISIS H⁻ Injector

3899

B.S. Drumm, A.P. Letchford, R.E. Williamson
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
M. Keelan
STFC/RAL, Chilton, Didcot, Oxon, United Kingdom

The energy range of the ISIS 70MeV H⁻ injected beam is reduced using an RF debunching cavity. The existing cavity consists of a mild steel vacuum vessel containing a water-cooled copper shell into which RF power is fed. The unit is made up of components designed for the 50 MeV Proton Linear Accelerator (PLA) which used to occupy the Rutherford Appleton Laboratory (RAL) site between 1957 and 1969. The component drawings date back to the late 1960s. Due to its age, complexity and a lack of spares, there is a need for a modern solution. This paper documents the development of a new debunching cavity for the ISIS neutron source.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI056

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)