IPAC2011 - List of Authors (Warsop, C.M.)

Paper	Title	Page
MOPS018	Simulation and Measurement of Half Integer Resonance in Coasting Beams on the ISIS Ring	637
	C.M. Warsop STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom D.J. Adams, B. Jones, B.G. Pine, H. V. Smith, R.E. Williamson STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	ISIS is the spallation neutron source at the Rutherford Appleton Laboratory in the UK. Operation centres on an 800 MeV rapid cycling synchrotron (RCS), which provides 3·10¹³ protons per pulse at 50 Hz, corresponding to a beam power of 0.2 MW. In common with many lower energy, high intensity proton rings, a key loss mechanism on ISIS is half integer resonance under space charge. This paper summarises experimental and simulation work studying half integer resonance in a “2D” coasting beam in the ISIS ring: understanding this is an essential prerequisite for explaining the more complicated case of RCS operation. For coasting beam experiments, the ring is reconfigured to storage ring mode with RF off and main magnets powered on DC current only. A 70 MeV beam is injected, painted appropriately, and manipulated so as to approach resonance. Understanding how the resonant condition develops is central to explaining observations, so realistic simulations of resonance, including injection, ramping of intensity and tunes are being developed. Results from the ORBIT code are presented and compared with experimental and theoretical results. Finally, future plans are summarized.

MOPS019	High Intensity Longitudinal Dynamics Studies for Higher Energy Injection into the ISIS Synchrotron	640
	R.E. Williamson, D.J. Adams, C.M. Warsop STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	ISIS is the world’s most productive pulsed neutron and muon source, at the Rutherford Appleton Laboratory in the UK. Operation is centred on a loss-limited 50 Hz proton synchrotron which accelerates 3·10¹³ protons per pulse from 70 MeV to 800 MeV, delivering a mean beam power of 0.2 MW. Present studies on ISIS upgrades are focussed on a new linac for higher energy injection into the existing ring, potentially increasing beam current through reduction in space charge and optimized injection. Studies assume injection of a chopped beam at 180 MeV and offer the possibility of beam powers in the 0.5 MW regime. A critical aspect of such an upgrade is the longitudinal dynamics, associated RF parameters, space charge levels and stringent requirements on beam loss. This paper outlines studies optimizing longitudinal parameters including key design requirements such as bunching factor and satisfying the Keil-Schnell-Boussard stability criterion throughout acceleration. Work developing and benchmarking the in-house longitudinal dynamics code used for these studies is also summarized.

WEPS104	Transverse Beam Dynamics for the ISIS Synchrotron with Higher Energy Injection	2754
	B.G. Pine, C.M. Warsop STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	ISIS is the spallation neutron source at the Rutherford Appleton Laboratory in the UK. Operation centres on an 800 MeV rapid cycling synchrotron, which provides 3·10¹³ protons per pulse at 50 Hz, corresponding to a beam power of 200 kW. Studies are underway to increase the energy of the ISIS linac from 70 to 180 MeV. This would reduce space charge in the synchrotron, and enable a larger current to be accumulated, possibly up to 0.5 MW. As part of the study, transverse beam dynamics have been re-examined on ISIS, building up models from incoherent space charge tune shift, through smooth focusing models with space charge to 2D alternating gradient lattice simulations. These later simulations, using the in-house space charge code Set, include harmonic perturbations to the focusing lattice, closed orbits and images. A clearer picture of the dynamics is emerging, where there may be important constraints on the highest intensities, including half integer resonance, image induced structure resonances and transverse instabilities.

WEPS106	Status of Injection Upgrade Studies for the ISIS Synchrotron	2760
	C.M. Warsop, D.J. Adams, D.J.S. Findlay, I.S.K. Gardner, S.J.S. Jago, B. Jones, R.J. Mathieson, S.J. Payne, B.G. Pine, A. Seville, H. V. Smith, J.W.G. Thomason, R.E. Williamson STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom J. Pasternak Imperial College of Science and Technology, Department of Physics, London, United Kingdom C.R. Prior, G.H. Rees STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom
	ISIS is the spallation neutron source at the Rutherford Appleton Laboratory in the UK. Operation centres on a high intensity proton accelerator, consisting of a 70 MeV linac and an 800 MeV rapid cycling synchrotron, which provides a beam power of 0.2 MW. Obsolescence issues are motivating plans to replace the ageing 70 MeV linac, and this paper summarises the status of studies looking at how a new, higher energy linac (~180 MeV) could be used to increase beam power in the existing synchrotron. Reduced space charge and optimized injection might allow beam powers in the 0.5 MW regime, thus providing a very cost effective upgrade. The key areas of study are: design of a practical injection straight and magnets; injection painting and dynamics; foil specifications; acceleration dynamics; transverse space charge; instabilities; RF beam loading; beam loss and activation; diagnostics and possible damping systems. Results from work on most of these topics suggest that beam powers of ~0.5 MW may well be possible, but a number of topics, particularly transverse stability, still look challenging. Conclusions so far are presented, as is progress on R&D on the main intensity limiting issues.

THPS057	Stripping Foil Simulations for ISIS Injection Upgrades	3556
	H. V. Smith, D.J. Adams, B. Jones, C.M. Warsop STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	ISIS, the pulsed neutron and muon spallation source located at the Rutherford Appleton Laboratory (UK), currently delivers a mean beam power of 0.2 MW to target. A 70 MeV H⁻ linear accelerator feeds into a 50 Hz, 800 MeV proton synchrotron (through a 0.3·10^-6 m Aluminium Oxide stripping foil), accelerating up to 3·10¹³ protons per pulse. Potential injection scheme upgrades, aiming to raise average beam power towards 0.5 MW with a new 180 MeV linear accelerator, are being studied. Detailed consideration of the injection stripping foil forms a key element of this study: scattering, stripping efficiency and foil lifetime are significant factors in determining loss levels, which consequently limit operational intensity. This paper describes the identification of a suitable stripping foil specification for successful 180 MeV H⁻ charge exchange injection into the ISIS synchrotron. Simulation code was developed to investigate electron stripping, scattering events and temperature rises, in order to witness their subsequent effect on foil lifetime. ANSYS models were also used to investigate the heat transfer and temperature distribution within thin foils.

Paper

Title

Page

Simulation and Measurement of Half Integer Resonance in Coasting Beams on the ISIS Ring

637

C.M. Warsop
STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom
D.J. Adams, B. Jones, B.G. Pine, H. V. Smith, R.E. Williamson
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom

ISIS is the spallation neutron source at the Rutherford Appleton Laboratory in the UK. Operation centres on an 800 MeV rapid cycling synchrotron (RCS), which provides 3·10¹³ protons per pulse at 50 Hz, corresponding to a beam power of 0.2 MW. In common with many lower energy, high intensity proton rings, a key loss mechanism on ISIS is half integer resonance under space charge. This paper summarises experimental and simulation work studying half integer resonance in a “2D” coasting beam in the ISIS ring: understanding this is an essential prerequisite for explaining the more complicated case of RCS operation. For coasting beam experiments, the ring is reconfigured to storage ring mode with RF off and main magnets powered on DC current only. A 70 MeV beam is injected, painted appropriately, and manipulated so as to approach resonance. Understanding how the resonant condition develops is central to explaining observations, so realistic simulations of resonance, including injection, ramping of intensity and tunes are being developed. Results from the ORBIT code are presented and compared with experimental and theoretical results. Finally, future plans are summarized.

MOPS019

High Intensity Longitudinal Dynamics Studies for Higher Energy Injection into the ISIS Synchrotron

640

R.E. Williamson, D.J. Adams, C.M. Warsop
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom

ISIS is the world’s most productive pulsed neutron and muon source, at the Rutherford Appleton Laboratory in the UK. Operation is centred on a loss-limited 50 Hz proton synchrotron which accelerates 3·10¹³ protons per pulse from 70 MeV to 800 MeV, delivering a mean beam power of 0.2 MW. Present studies on ISIS upgrades are focussed on a new linac for higher energy injection into the existing ring, potentially increasing beam current through reduction in space charge and optimized injection. Studies assume injection of a chopped beam at 180 MeV and offer the possibility of beam powers in the 0.5 MW regime. A critical aspect of such an upgrade is the longitudinal dynamics, associated RF parameters, space charge levels and stringent requirements on beam loss. This paper outlines studies optimizing longitudinal parameters including key design requirements such as bunching factor and satisfying the Keil-Schnell-Boussard stability criterion throughout acceleration. Work developing and benchmarking the in-house longitudinal dynamics code used for these studies is also summarized.

WEPS104

Transverse Beam Dynamics for the ISIS Synchrotron with Higher Energy Injection

2754

B.G. Pine, C.M. Warsop
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom

ISIS is the spallation neutron source at the Rutherford Appleton Laboratory in the UK. Operation centres on an 800 MeV rapid cycling synchrotron, which provides 3·10¹³ protons per pulse at 50 Hz, corresponding to a beam power of 200 kW. Studies are underway to increase the energy of the ISIS linac from 70 to 180 MeV. This would reduce space charge in the synchrotron, and enable a larger current to be accumulated, possibly up to 0.5 MW. As part of the study, transverse beam dynamics have been re-examined on ISIS, building up models from incoherent space charge tune shift, through smooth focusing models with space charge to 2D alternating gradient lattice simulations. These later simulations, using the in-house space charge code Set, include harmonic perturbations to the focusing lattice, closed orbits and images. A clearer picture of the dynamics is emerging, where there may be important constraints on the highest intensities, including half integer resonance, image induced structure resonances and transverse instabilities.

WEPS106

Status of Injection Upgrade Studies for the ISIS Synchrotron

2760

C.M. Warsop, D.J. Adams, D.J.S. Findlay, I.S.K. Gardner, S.J.S. Jago, B. Jones, R.J. Mathieson, S.J. Payne, B.G. Pine, A. Seville, H. V. Smith, J.W.G. Thomason, R.E. Williamson
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
J. Pasternak
Imperial College of Science and Technology, Department of Physics, London, United Kingdom
C.R. Prior, G.H. Rees
STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom

ISIS is the spallation neutron source at the Rutherford Appleton Laboratory in the UK. Operation centres on a high intensity proton accelerator, consisting of a 70 MeV linac and an 800 MeV rapid cycling synchrotron, which provides a beam power of 0.2 MW. Obsolescence issues are motivating plans to replace the ageing 70 MeV linac, and this paper summarises the status of studies looking at how a new, higher energy linac (~180 MeV) could be used to increase beam power in the existing synchrotron. Reduced space charge and optimized injection might allow beam powers in the 0.5 MW regime, thus providing a very cost effective upgrade. The key areas of study are: design of a practical injection straight and magnets; injection painting and dynamics; foil specifications; acceleration dynamics; transverse space charge; instabilities; RF beam loading; beam loss and activation; diagnostics and possible damping systems. Results from work on most of these topics suggest that beam powers of ~0.5 MW may well be possible, but a number of topics, particularly transverse stability, still look challenging. Conclusions so far are presented, as is progress on R&D on the main intensity limiting issues.

THPS057

Stripping Foil Simulations for ISIS Injection Upgrades

3556

H. V. Smith, D.J. Adams, B. Jones, C.M. Warsop
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom

ISIS, the pulsed neutron and muon spallation source located at the Rutherford Appleton Laboratory (UK), currently delivers a mean beam power of 0.2 MW to target. A 70 MeV H⁻ linear accelerator feeds into a 50 Hz, 800 MeV proton synchrotron (through a 0.3·10^-6 m Aluminium Oxide stripping foil), accelerating up to 3·10¹³ protons per pulse. Potential injection scheme upgrades, aiming to raise average beam power towards 0.5 MW with a new 180 MeV linear accelerator, are being studied. Detailed consideration of the injection stripping foil forms a key element of this study: scattering, stripping efficiency and foil lifetime are significant factors in determining loss levels, which consequently limit operational intensity. This paper describes the identification of a suitable stripping foil specification for successful 180 MeV H⁻ charge exchange injection into the ISIS synchrotron. Simulation code was developed to investigate electron stripping, scattering events and temperature rises, in order to witness their subsequent effect on foil lifetime. ANSYS models were also used to investigate the heat transfer and temperature distribution within thin foils.