HB2014 - List of Authors (Williamson, R.E.)

Paper

Title

Page

Simulations of the Head-tail Instability on the ISIS Synchrotron

113

R.E. Williamson, D.J. Adams, B. Jones, C.M. Warsop
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
V. Kornilov
GSI, Darmstadt, Germany

ISIS is the pulsed spallation 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 (ppp) from 70 MeV to 800 MeV, delivering a mean beam power of 0.2 MW. Present studies are focussed on key aspects of high intensity beam dynamics with a view to increasing operational intensity, understanding loss mechanisms and identifying possible upgrade routes. Of particular interest is the head-tail instability observed on ISIS, which is currently the main limitation on beam intensity. This paper presents initial simulations using HEADTAIL to compare with experimental data taken on the ISIS synchrotron. The details and assumptions of the impedance model and simulations are discussed. Plans for future head-tail measurements, simulations and analysis are outlined.

MOPAB40

Studies of Loss Mechanisms Associated with the Half Integer Limit on the ISIS Ring

123

C.M. Warsop, D.J. Adams, B. Jones, B.G. Pine, H. V. Smith, C.C. Wilcox, 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. The facility centres on an 800 MeV rapid cycling proton synchrotron, which provides 0.2 MW of beam power operating at high levels of transverse space charge (peak incoherent tune shift ~ 0.5), but with low loss. Half integer resonance is considered to be a main driver for loss that limits the intensity in high power, medium energy proton rings like ISIS. However, the detailed mechanisms causing loss as the half integer limit is approached are not well understood, particularly in the context of a real machine. In this paper we report progress on experiments on the ISIS synchrotron inducing half integer loss, comparing with detailed simulations and attempts to relate these to simplified theoretical and simulation models. Effects of longitudinal motion on growth mechanisms, e.g. in coasting, “frozen” bunched and rapid cycling bunched beams are discussed, as is how these losses might be minimised and thus the real space charge limit effectively increased.

TUO3LR03

High Intensity Loss Mechanisms on the ISIS Rapid Cycling Synchrotron

203

C.M. Warsop, D.J. Adams, B. Jones, S.J. Payne, B.G. Pine, H. V. Smith, R.E. Williamson
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
V. Kornilov
GSI, Darmstadt, Germany

ISIS is the spallation neutron source at the Rutherford Appleton laboratory in the UK. Operation centres on a loss limited, 800 MeV, 50 Hz proton synchrotron which delivers 0.2 MW to two targets. Understanding loss mechanisms on the ISIS ring is important for optimal operation, machine developments and upgrades, as well as improving understanding for future machines. The high space charge levels, combined with the low loss achieved for high power operation, makes the ring an ideal tool for studying the physics of beam loss, particularly in a fast ramping context. The ability to reconfigure the beam in storage ring mode, and ongoing developments of diagnostics and beam measurements, are allowing detailed studies of image effects, resonances, beam stability and activation. We summarise recent work and progress on these topics, comparing with theory and simulation where appropriate.

Slides TUO3LR03 [2.534 MB]

WEO1LR02

Thresholds of the Head-Tail Instability in Bunches with Space Charge

240

V. Kornilov, O. Boine-Frankenheim
GSI, Darmstadt, Germany
D.J. Adams, B. Jones, B.G. Pine, C.M. Warsop, R.E. Williamson
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom

Recent experimental studies of the unstable head-tail modes in the ISIS synchrotron (RAL, UK) provided intriguing findings about the intensity thresholds for the instability/stability along the acceleration ramp for different bunch parameters in single-rf and dual-rf operation. We explain the role of space-charge and the related Landau damping using particle tracking simulations and an airbag-bunch theory, and relate the observations to the classical single-rf, no space-charge theories in order to identify the driving impedances.

Slides WEO1LR02 [3.203 MB]

THO3LR02

Ring Simulation and Beam Dynamics Studies for ISIS Upgrades 0.5 to 10 MW

374

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

Various upgrade routes are under study for the ISIS spallation neutron source at RAL in the UK. Recent work has concentrated on upgrading the injector, increasing injection energy from 70 to 180 MeV, and studying the challenging possibility of reaching powers up to 0.5 MW in the existing 800 MeV RCS. Studies for the longer term are exploring the possibilities of a 5 MW, 3.2 GeV RCS that could form part of a new stand-alone 10+ MW next generation “ISIS II” facility. A central part of these ring studies is the use of computer simulations to guide designs, for example optimising the injection painting configuration and providing an indication of expected loss levels. Here we summarise the computer models used, indicate where benchmarking has been possible, describe optimisations and results from studies, and outline the main uncertainties. Understanding the limitations in high power RCS accelerators is an important part of determining optimal facility designs for the future.

Slides THO3LR02 [2.658 MB]

Paper	Title	Page
MOPAB38	Simulations of the Head-tail Instability on the ISIS Synchrotron	113
	R.E. Williamson, D.J. Adams, B. Jones, C.M. Warsop STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom V. Kornilov GSI, Darmstadt, Germany
	ISIS is the pulsed spallation 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 (ppp) from 70 MeV to 800 MeV, delivering a mean beam power of 0.2 MW. Present studies are focussed on key aspects of high intensity beam dynamics with a view to increasing operational intensity, understanding loss mechanisms and identifying possible upgrade routes. Of particular interest is the head-tail instability observed on ISIS, which is currently the main limitation on beam intensity. This paper presents initial simulations using HEADTAIL to compare with experimental data taken on the ISIS synchrotron. The details and assumptions of the impedance model and simulations are discussed. Plans for future head-tail measurements, simulations and analysis are outlined.

MOPAB40	Studies of Loss Mechanisms Associated with the Half Integer Limit on the ISIS Ring	123
	C.M. Warsop, D.J. Adams, B. Jones, B.G. Pine, H. V. Smith, C.C. Wilcox, 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. The facility centres on an 800 MeV rapid cycling proton synchrotron, which provides 0.2 MW of beam power operating at high levels of transverse space charge (peak incoherent tune shift ~ 0.5), but with low loss. Half integer resonance is considered to be a main driver for loss that limits the intensity in high power, medium energy proton rings like ISIS. However, the detailed mechanisms causing loss as the half integer limit is approached are not well understood, particularly in the context of a real machine. In this paper we report progress on experiments on the ISIS synchrotron inducing half integer loss, comparing with detailed simulations and attempts to relate these to simplified theoretical and simulation models. Effects of longitudinal motion on growth mechanisms, e.g. in coasting, “frozen” bunched and rapid cycling bunched beams are discussed, as is how these losses might be minimised and thus the real space charge limit effectively increased.

TUO3LR03	High Intensity Loss Mechanisms on the ISIS Rapid Cycling Synchrotron	203
	C.M. Warsop, D.J. Adams, B. Jones, S.J. Payne, B.G. Pine, H. V. Smith, R.E. Williamson STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom V. Kornilov GSI, Darmstadt, Germany
	ISIS is the spallation neutron source at the Rutherford Appleton laboratory in the UK. Operation centres on a loss limited, 800 MeV, 50 Hz proton synchrotron which delivers 0.2 MW to two targets. Understanding loss mechanisms on the ISIS ring is important for optimal operation, machine developments and upgrades, as well as improving understanding for future machines. The high space charge levels, combined with the low loss achieved for high power operation, makes the ring an ideal tool for studying the physics of beam loss, particularly in a fast ramping context. The ability to reconfigure the beam in storage ring mode, and ongoing developments of diagnostics and beam measurements, are allowing detailed studies of image effects, resonances, beam stability and activation. We summarise recent work and progress on these topics, comparing with theory and simulation where appropriate.
	Slides TUO3LR03 [2.534 MB]

WEO1LR02	Thresholds of the Head-Tail Instability in Bunches with Space Charge	240
	V. Kornilov, O. Boine-Frankenheim GSI, Darmstadt, Germany D.J. Adams, B. Jones, B.G. Pine, C.M. Warsop, R.E. Williamson STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	Recent experimental studies of the unstable head-tail modes in the ISIS synchrotron (RAL, UK) provided intriguing findings about the intensity thresholds for the instability/stability along the acceleration ramp for different bunch parameters in single-rf and dual-rf operation. We explain the role of space-charge and the related Landau damping using particle tracking simulations and an airbag-bunch theory, and relate the observations to the classical single-rf, no space-charge theories in order to identify the driving impedances.
	Slides WEO1LR02 [3.203 MB]

THO3LR02	Ring Simulation and Beam Dynamics Studies for ISIS Upgrades 0.5 to 10 MW	374
	D.J. Adams, B. Jones, B.G. Pine, H. V. Smith, C.M. Warsop, R.E. Williamson STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom C.R. Prior, G.H. Rees STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom
	Various upgrade routes are under study for the ISIS spallation neutron source at RAL in the UK. Recent work has concentrated on upgrading the injector, increasing injection energy from 70 to 180 MeV, and studying the challenging possibility of reaching powers up to 0.5 MW in the existing 800 MeV RCS. Studies for the longer term are exploring the possibilities of a 5 MW, 3.2 GeV RCS that could form part of a new stand-alone 10+ MW next generation “ISIS II” facility. A central part of these ring studies is the use of computer simulations to guide designs, for example optimising the injection painting configuration and providing an indication of expected loss levels. Here we summarise the computer models used, indicate where benchmarking has been possible, describe optimisations and results from studies, and outline the main uncertainties. Understanding the limitations in high power RCS accelerators is an important part of determining optimal facility designs for the future.
	Slides THO3LR02 [2.658 MB]