IPAC2011 - Classification: 05 Beam Dynamics and Electromagnetic Fields / D03 High Intensity in Circular Machines

Paper

Title

Page

Electron-cloud Pinch Dynamics in Presence of Lattice Magnet Fields

586

G. Franchetti
GSI, Darmstadt, Germany
F. Zimmermann
CERN, Geneva, Switzerland

The pinch of the electron cloud due to a passing proton bunch was extensively studied in a field free region and in a dipolar magnetic field. For the latter study, a strong field approximation helped to formulate the equations of motion and to understand the complex electron pinch dynamics, which exhibited some similarities with the field-free situation. Here we extend the analysis to the case of electron pinch in quadrupoles and in sextupoles. We discuss the limits of validity for the strong field approximation and we evaluate the relative magnitude of the peak tune shift along the bunch expected for the different fields.

MOPS002

Mitigation of Space Charge and Nonlinear Resonance Induced Beam Loss in SIS100

589

G. Franchetti
GSI, Darmstadt, Germany

The control of beam loss in SIS100 is essential for avoiding vacuum instability and guarantee the delivery of the foreseen beam intensity. On the other hand simulations show that the simultaneous presence of space charge and lattice resonances creates during 1 second cycle a progressive beam loss exceeding the limit of 5%. Until now the mechanism of periodic resonance crossing were suspected to be, in conjunction with pure dynamic aperture effects, at the base of the beam loss. In this proceeding we present the state of the art in the beam loss prediction and we prove that the periodic resonance crossing is the deteriorating mechanism, and show that the compensation of a relevant resonance intercepting the space charge tune spread sensibly mitigate the beam loss. A short discussion on beam loss during acceleration is addressed as well.

MOPS003

Coherent Beam-beam Resonances in SuperB with Asymmetric Rings

592

M. Zobov
INFN/LNF, Frascati (Roma), Italy
Y. Zhang
IHEP Beijing, Beijing, People's Republic of China

One of the latest options of SuperB foresees exploiting rings with unequal circumferences. In such a configuration additional coherent beam-beam resonances can arise. In this paper we discuss the possible impact of the resonances on beam dynamics in SuperB, maximum achievable tune shifts and working point choice.

MOPS004

Mitigation of Beam Instability due to Space Charge Effects at 3 GeV RCS in J-PARC

595

Y. Shobuda, M. Yamamoto
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
Y.H. Chin
KEK, Ibaraki, Japan
F. Tamura
KEK/JAEA, Ibaraki-Ken, Japan

In order to accomplish high intensity proton beams, it is important to identify the impedance source in accelerators. At 3 GeV rapid cycling synchrotron (RCS) in Japan Proton Research Complex (J-PARC), the kicker impedance is the most dominant among such impedance sources. Beam instability can be observed by correcting chromaticity during the acceleration. Growth rate due to the beam instability can be reduced by making peak current larger (bunching factor smaller). In other words, it is experimentally found that space charge effects mitigate the beam instability.

MOPS005

Beam Dynamics Simulations of J-PARC Main Ring for Upgrade Plan of Fast Extraction Operation

598

Y. Sato, K. Hara, S. Igarashi, T. Koseki, K. Ohmi, C. Ohmori, M. Tomizawa
KEK, Ibaraki, Japan
H. Hotchi
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan

Beam loss simulations under space charge effects are necessary to seek higher intensity proton beams. This paper presents simulations for fast extraction operation of Japan Proton Accelerator Research Complex (J-PARC) Main Ring. For upgrade plan, increasing protons per bunch and making higher repetition pattern are considered. Their optimal balance is discussed to minimize beam losses for aimed beam power considering space charge effects. We found that to optimize RF voltage pattern is a strong key to reduce beam losses for higher repetition. As benchmark works, we compare our simulations with the measured beam loss in our past operation.

MOPS006

Beam Tilt due to Transverse Wakefields for DAΦNE, SuperB, KEKB and SuperKEKB

601

D.M. Zhou, K. Ohmi
KEK, Ibaraki, Japan
A. Chao
SLAC, Menlo Park, California, USA

When a beam bunch traverses a transverse impedance, the bunch head generates a transverse wakefield that kicks the bunch tail, generating a betatron motion of the tail relative to the head. In a storage ring, in a steady state, this kick to the bunch tail produces a transverse closed orbit (e.g. in the y-direction) of the bunch tail relative to the bunch head, which means the beam now has a y-z tilt. Such beam tilt due to transverse wakefields may cause a loss of luminosity in storage ring colliders or loss of brightness in light sources. In this paper, we present a preliminary study of the beam tilt effect for the colliders DAΦNE, SuperB, KEKB and SuperKEKB.

MOPS008

Simulation of Longitudinal Emittance Control in J-PARC RCS for 400 MeV Injection

607

M. Yamamoto, M. Nomura, A. Schnase, T. Shimada, F. Tamura
JAEA/J-PARC, Tokai-mura, Japan
E. Ezura, K. Hara, K. Hasegawa, C. Ohmori, A. Takagi, K. Takata, M. Toda, M. Yoshii
KEK, Ibaraki, Japan

The injection energy upgrade of the J-PARC RCS from 181 MeV to 400 MeV is scheduled, this is necessary to achieve the design beam intensity. The high intensity beam is delivered to the MR, and the space charge effect at the MR injection should be alleviated by optimizing the longitudinal beam emittance at RCS extraction. This is realized by matching the shape of the beam emittance between the RCS and the MR. We describe the results of particle tracking simulation with the longitudinal emittance control during the whole acceleration period of the RCS.

MOPS009

Probing Intensity Limits of LHC-type Bunches in the CERN SPS with Nominal Optics

610

B. Salvant, G. Adrian, D.J. Allen, O. Andujar, T. Argyropoulos, J. Axensalva, J. Baldy, H. Bartosik, S. Cettour Cave, F. Chapuis, J.F. Comblin, K. Cornelis, D.G. Cotte, K. Cunnington, H. Damerau, M. Delrieux, J.L. Duran-Lopez, A. Findlay, J. Fleuret, F. Follin, P. Freyermuth, H. Genoud, S.S. Gilardoni, A. Guerrero, S. Hancock, K. Hanke, O. Hans, R. Hazelaar, W. Höfle, L.K. Jensen, J. Kuczerowski, Y. Le Borgne, R. Maillet, D. Manglunki, S. Massot, E. Matli, G. Metral, B. Mikulec, E. Métral, J.-M. Nonglaton, E. Ovalle, L. Pereira, F.C. Peters, A. Rey, J.P. Ridewood, G. Rumolo, J.L. Sanchez Alvarez, E.N. Shaposhnikova, R.R. Steerenberg, R.J. Steinhagen, J. Tan, B. Vandorpe, E. Veyrunes
CERN, Geneva, Switzerland

Some of the upgrade scenarios of the high-luminosity LHC require large intensity per bunch from the injector chain. Single bunch beams with intensities of up to 3.5 to 4·10¹¹ p/b and nominal emittances were successfully produced in the PS Complex and delivered to the SPS in 2010. This contribution presents results of studies with this new intense beam in the SPS to probe single bunch intensity limitations with nominal gamma transition. In particular, the vertical Transverse Mode Coupling Instability (TMCI) threshold with low chromaticity was observed at 1.6·10¹¹ p/b for single nominal LHC bunches in the SPS. With increased vertical chromaticity, larger intensities could be injected, stored along the flat bottom and accelerated up to 450 GeV/c. However, significant losses and/or transverse emittance blow up were then observed. Longitudinal and transverse optimization efforts in the PSB, PS and SPS were put in place to minimize this beam degradation and succeeded to obtain single 2.3·10¹¹ p/b LHC type bunches with satisfying parameters at extraction of the SPS.

MOPS012

Optics Considerations for Lowering Transition Energy in the SPS

619

H. Bartosik, G. Arduini, Y. Papaphilippou
CERN, Geneva, Switzerland

Beam stability for high intensity LHC beams in the SPS can be improved by increasing the slippage factor, i.e. reducing the transition energy. In this paper, possible ways of modifying the optics of the SPS for lower transition energy are reviewed. In particular, a threefold increase of the slippage factor at injection can be achieved by decreasing the integer part of the tunes by 6 units. The properties of this new low-transition optics are compared with the nominal SPS optics, including working point and resonance behavior. Possible limitations are discussed.

MOPS014

Tune and Space Charge Studies for High-brightness and High-intensity Beams at CERN PS

625

S.S. Gilardoni, S. Aumon, J. Brenas, P. Freyermuth, A. Huschauer, R. Maillet, E. Matli, R.R. Steerenberg, B. Vandorpe
CERN, Geneva, Switzerland
E. Benedetto
National Technical University of Athens, Zografou, Greece

The current 1.4 GeV CERN PS injection energy limits the maximum intensity required by the future High-Luminosity LHC. The bare-machine large chromaticity combined with the non-linear space charge forces make high-brightness and high-intensity beams crossing betatron resonances along the injection flat bottom, inducing transverse emittance blow-up and beam losses. A scan of the working point plane {Qx,Qy} was done in order to identify beam destructive resonances, in the framework of a possible 2 GeV injection energy upgrade which would reduce the space charge effect on the tune. Experiments were carried out in order to review the maximum space charge tune shift for which no transverse emittance blow-up is observed. The results of measurements and simulations will be presented in this paper.

MOPS016

First Observations of Intensity-dependent Effects for Transversally Split Beams

631

S.S. Gilardoni, M. Giovannozzi
CERN, Geneva, Switzerland

During the commissioning of the CERN PS Multi-Turn Extraction (MTE) tests with different beam intensities were performed. The beam current before transverse splitting was varied and the properties of the five beamlets obtained by crossing the fourth-order horizontal resonance were studied. A clear dependence of the beamlets’ parameters on the total intensity was found, which is a first observation of intensity-dependent effects for such a peculiar beam type. The experimental results are presented and discussed in this paper.

MOPS017

Simulation Studies of Macro-particles Falling into the LHC Proton Beam

634

F. Zimmermann, T. Baer, M. Giovannozzi, E.B. Holzer, E. Nebot Del Busto, A. Nordt, M. Sapinski
CERN, Geneva, Switzerland
N. Fuster
Valencia University, Atomic Molecular and Nuclear Physics Department, Valencia, Spain
Z. Yang
EPFL, Lausanne, Switzerland

We report updated simulations on the interaction of macro-particles falling from the top of the vacuum chamber into the circulating LHC proton beam. The path and charge state of micron size micro-particles are computed together with the resulting beam losses, which – if high enough - can lead to the local quench of SC magnets. The simulated time evolution of the beam loss is compared with observations in order to constrain some macro-particle parameters. We also discuss the possibility of a "multiple crossing" by the same macro-particle, the effect of a strong dipole field, and the dependence of peak loss rate and loss duration on beam current and on beam size.

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.

MOPS021

Beam Dynamics of a Compact SC Isochronous Cyclotron - Preliminary Study of Central Region*

643

J.X. Zhang, T.A. Antaya, R.E. Block
MIT/PSFC, Cambridge, Massachusetts, USA

Funding: Pennsylvania State University ARL S11-07 and N00024-02-D-6604 US Defense Threat Reduction Agency
A compact high field superconducting isochronous cyclotron, Megatron (K250), is designed as a proof-of-principle for a single stage high power proton accelerator. This cyclotron is to accelerate proton to a final energy of 250 MeV with two 45° Dees with a radius ~40 cm. By employing a 20 mA external ECR proton source, the injected proton beam currents at high brightness are foreseen. Using phase selection in the center, a fully magnetized elliptical pole, low energy gain per turn, a precise relation between momentum and radius at large radius are expected. Two goals, a) to use this relationship to develop multi-turn extraction with passive elements only, to achieve a high external proton beam intensity (~1 mA); and b) to see if it is possible to achieve a high extraction efficiency (> 99%) without single turn extraction, with an energy spread |DE/E| ~0.1%. The RF acceleration is on the first harmonic with ωrf=ω0~64 MHz. Superconductor coils will provide a central field of B0 = 4.3 T and a peak hill field of 6.6 T. The general beam dynamics studies will be performed. Precise central field design including space charge effect will be shown in the presentation.

THOBA01

Electron Cloud Observations in LHC

2862

G. Rumolo, G. Arduini, V. Baglin, H. Bartosik, P. Baudrenghien, N. Biancacci, G. Bregliozzi, S.D. Claudet, R. De Maria, J. Esteban Muller, M. Favier, C. Hansen, W. Höfle, J.M. Jimenez, V. Kain, E. Koukovini, G. Lanza, K.S.B. Li, G.H.I. Maury Cuna, E. Métral, G. Papotti, T. Pieloni, F. Roncarolo, B. Salvant, E.N. Shaposhnikova, R.J. Steinhagen, L.J. Tavian, D. Valuch, W. Venturini Delsolaro, F. Zimmermann
CERN, Geneva, Switzerland
C.M. Bhat
Fermilab, Batavia, USA
U. Iriso
CELLS-ALBA Synchrotron, Cerdanyola del Vallès, Spain
N. Mounet, C. Zannini
EPFL, Lausanne, Switzerland

Operation of LHC with bunch trains different spacings has revealed the formation of an electron cloud inside the machine. The main observations of electron cloud build-up are the pressure rise measured at the vacuum gauges in the warm regions, as well as the increase of the beam screen temperature in the cold regions due to an additional heat load. The effects of the electron cloud were also visible as a strong instability and emittance growth affecting the last bunches of longer trains, which could be improved running with higher chromaticity and/or larger transverse emittances. A summary of the 2010 and 2011 observations and measurements and a comparison with existing models will be presented. The efficiency of scrubbing and scrubbing strategies to improve the machine running performance will be also briefly discussed.

Slides THOBA01 [2.911 MB]

FRXAA01

Theory of Microwave Instability and Coherent Synchrotron Radiation in Electron Storage Rings

3774

Y. Cai
SLAC, Menlo Park, California, USA

Funding: This work was supported by Department of Energy Contract No. DE-AC02-76SF00515.
Bursting of coherent synchrotron radiation has been observed and in fact used to generate THz radiation in many electron storage rings. In order to understand and control the bursting, we return to the study of the microwave instability. In this talk, we will report on the theoretical understanding, including recent developments, of the microwave instability in electron storage rings. The historical progress of the theories will be surveyed, starting from the dispersion relation of coasting beams, to the work of Sacherer on a bunched beam, and ending with the Oide and Yokoya method of discretization. This theoretical survey will be supplemented with key experimental results over the years. Finally, we will describe the recent theoretical development of utilizing the Laguerre polynomials in the presence of potential-well distortion. This self-consistent method will be applied to study the microwave instability driven by commonly known impedances, including that of coherent synchrotron radiation.

Slides FRXAA01 [0.948 MB]

Paper	Title	Page
MOPS001	Electron-cloud Pinch Dynamics in Presence of Lattice Magnet Fields	586
	G. Franchetti GSI, Darmstadt, Germany F. Zimmermann CERN, Geneva, Switzerland
	The pinch of the electron cloud due to a passing proton bunch was extensively studied in a field free region and in a dipolar magnetic field. For the latter study, a strong field approximation helped to formulate the equations of motion and to understand the complex electron pinch dynamics, which exhibited some similarities with the field-free situation. Here we extend the analysis to the case of electron pinch in quadrupoles and in sextupoles. We discuss the limits of validity for the strong field approximation and we evaluate the relative magnitude of the peak tune shift along the bunch expected for the different fields.

MOPS002	Mitigation of Space Charge and Nonlinear Resonance Induced Beam Loss in SIS100	589
	G. Franchetti GSI, Darmstadt, Germany
	The control of beam loss in SIS100 is essential for avoiding vacuum instability and guarantee the delivery of the foreseen beam intensity. On the other hand simulations show that the simultaneous presence of space charge and lattice resonances creates during 1 second cycle a progressive beam loss exceeding the limit of 5%. Until now the mechanism of periodic resonance crossing were suspected to be, in conjunction with pure dynamic aperture effects, at the base of the beam loss. In this proceeding we present the state of the art in the beam loss prediction and we prove that the periodic resonance crossing is the deteriorating mechanism, and show that the compensation of a relevant resonance intercepting the space charge tune spread sensibly mitigate the beam loss. A short discussion on beam loss during acceleration is addressed as well.

MOPS003	Coherent Beam-beam Resonances in SuperB with Asymmetric Rings	592
	M. Zobov INFN/LNF, Frascati (Roma), Italy Y. Zhang IHEP Beijing, Beijing, People's Republic of China
	One of the latest options of SuperB foresees exploiting rings with unequal circumferences. In such a configuration additional coherent beam-beam resonances can arise. In this paper we discuss the possible impact of the resonances on beam dynamics in SuperB, maximum achievable tune shifts and working point choice.

MOPS004	Mitigation of Beam Instability due to Space Charge Effects at 3 GeV RCS in J-PARC	595
	Y. Shobuda, M. Yamamoto JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan Y.H. Chin KEK, Ibaraki, Japan F. Tamura KEK/JAEA, Ibaraki-Ken, Japan
	In order to accomplish high intensity proton beams, it is important to identify the impedance source in accelerators. At 3 GeV rapid cycling synchrotron (RCS) in Japan Proton Research Complex (J-PARC), the kicker impedance is the most dominant among such impedance sources. Beam instability can be observed by correcting chromaticity during the acceleration. Growth rate due to the beam instability can be reduced by making peak current larger (bunching factor smaller). In other words, it is experimentally found that space charge effects mitigate the beam instability.

MOPS005	Beam Dynamics Simulations of J-PARC Main Ring for Upgrade Plan of Fast Extraction Operation	598
	Y. Sato, K. Hara, S. Igarashi, T. Koseki, K. Ohmi, C. Ohmori, M. Tomizawa KEK, Ibaraki, Japan H. Hotchi JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
	Beam loss simulations under space charge effects are necessary to seek higher intensity proton beams. This paper presents simulations for fast extraction operation of Japan Proton Accelerator Research Complex (J-PARC) Main Ring. For upgrade plan, increasing protons per bunch and making higher repetition pattern are considered. Their optimal balance is discussed to minimize beam losses for aimed beam power considering space charge effects. We found that to optimize RF voltage pattern is a strong key to reduce beam losses for higher repetition. As benchmark works, we compare our simulations with the measured beam loss in our past operation.

MOPS006	Beam Tilt due to Transverse Wakefields for DAΦNE, SuperB, KEKB and SuperKEKB	601
	D.M. Zhou, K. Ohmi KEK, Ibaraki, Japan A. Chao SLAC, Menlo Park, California, USA
	When a beam bunch traverses a transverse impedance, the bunch head generates a transverse wakefield that kicks the bunch tail, generating a betatron motion of the tail relative to the head. In a storage ring, in a steady state, this kick to the bunch tail produces a transverse closed orbit (e.g. in the y-direction) of the bunch tail relative to the bunch head, which means the beam now has a y-z tilt. Such beam tilt due to transverse wakefields may cause a loss of luminosity in storage ring colliders or loss of brightness in light sources. In this paper, we present a preliminary study of the beam tilt effect for the colliders DAΦNE, SuperB, KEKB and SuperKEKB.

MOPS008	Simulation of Longitudinal Emittance Control in J-PARC RCS for 400 MeV Injection	607
	M. Yamamoto, M. Nomura, A. Schnase, T. Shimada, F. Tamura JAEA/J-PARC, Tokai-mura, Japan E. Ezura, K. Hara, K. Hasegawa, C. Ohmori, A. Takagi, K. Takata, M. Toda, M. Yoshii KEK, Ibaraki, Japan
	The injection energy upgrade of the J-PARC RCS from 181 MeV to 400 MeV is scheduled, this is necessary to achieve the design beam intensity. The high intensity beam is delivered to the MR, and the space charge effect at the MR injection should be alleviated by optimizing the longitudinal beam emittance at RCS extraction. This is realized by matching the shape of the beam emittance between the RCS and the MR. We describe the results of particle tracking simulation with the longitudinal emittance control during the whole acceleration period of the RCS.

MOPS009	Probing Intensity Limits of LHC-type Bunches in the CERN SPS with Nominal Optics	610
	B. Salvant, G. Adrian, D.J. Allen, O. Andujar, T. Argyropoulos, J. Axensalva, J. Baldy, H. Bartosik, S. Cettour Cave, F. Chapuis, J.F. Comblin, K. Cornelis, D.G. Cotte, K. Cunnington, H. Damerau, M. Delrieux, J.L. Duran-Lopez, A. Findlay, J. Fleuret, F. Follin, P. Freyermuth, H. Genoud, S.S. Gilardoni, A. Guerrero, S. Hancock, K. Hanke, O. Hans, R. Hazelaar, W. Höfle, L.K. Jensen, J. Kuczerowski, Y. Le Borgne, R. Maillet, D. Manglunki, S. Massot, E. Matli, G. Metral, B. Mikulec, E. Métral, J.-M. Nonglaton, E. Ovalle, L. Pereira, F.C. Peters, A. Rey, J.P. Ridewood, G. Rumolo, J.L. Sanchez Alvarez, E.N. Shaposhnikova, R.R. Steerenberg, R.J. Steinhagen, J. Tan, B. Vandorpe, E. Veyrunes CERN, Geneva, Switzerland
	Some of the upgrade scenarios of the high-luminosity LHC require large intensity per bunch from the injector chain. Single bunch beams with intensities of up to 3.5 to 4·10¹¹ p/b and nominal emittances were successfully produced in the PS Complex and delivered to the SPS in 2010. This contribution presents results of studies with this new intense beam in the SPS to probe single bunch intensity limitations with nominal gamma transition. In particular, the vertical Transverse Mode Coupling Instability (TMCI) threshold with low chromaticity was observed at 1.6·10¹¹ p/b for single nominal LHC bunches in the SPS. With increased vertical chromaticity, larger intensities could be injected, stored along the flat bottom and accelerated up to 450 GeV/c. However, significant losses and/or transverse emittance blow up were then observed. Longitudinal and transverse optimization efforts in the PSB, PS and SPS were put in place to minimize this beam degradation and succeeded to obtain single 2.3·10¹¹ p/b LHC type bunches with satisfying parameters at extraction of the SPS.

MOPS012	Optics Considerations for Lowering Transition Energy in the SPS	619
	H. Bartosik, G. Arduini, Y. Papaphilippou CERN, Geneva, Switzerland
	Beam stability for high intensity LHC beams in the SPS can be improved by increasing the slippage factor, i.e. reducing the transition energy. In this paper, possible ways of modifying the optics of the SPS for lower transition energy are reviewed. In particular, a threefold increase of the slippage factor at injection can be achieved by decreasing the integer part of the tunes by 6 units. The properties of this new low-transition optics are compared with the nominal SPS optics, including working point and resonance behavior. Possible limitations are discussed.

MOPS014	Tune and Space Charge Studies for High-brightness and High-intensity Beams at CERN PS	625
	S.S. Gilardoni, S. Aumon, J. Brenas, P. Freyermuth, A. Huschauer, R. Maillet, E. Matli, R.R. Steerenberg, B. Vandorpe CERN, Geneva, Switzerland E. Benedetto National Technical University of Athens, Zografou, Greece
	The current 1.4 GeV CERN PS injection energy limits the maximum intensity required by the future High-Luminosity LHC. The bare-machine large chromaticity combined with the non-linear space charge forces make high-brightness and high-intensity beams crossing betatron resonances along the injection flat bottom, inducing transverse emittance blow-up and beam losses. A scan of the working point plane {Qx,Qy} was done in order to identify beam destructive resonances, in the framework of a possible 2 GeV injection energy upgrade which would reduce the space charge effect on the tune. Experiments were carried out in order to review the maximum space charge tune shift for which no transverse emittance blow-up is observed. The results of measurements and simulations will be presented in this paper.

MOPS016	First Observations of Intensity-dependent Effects for Transversally Split Beams	631
	S.S. Gilardoni, M. Giovannozzi CERN, Geneva, Switzerland
	During the commissioning of the CERN PS Multi-Turn Extraction (MTE) tests with different beam intensities were performed. The beam current before transverse splitting was varied and the properties of the five beamlets obtained by crossing the fourth-order horizontal resonance were studied. A clear dependence of the beamlets’ parameters on the total intensity was found, which is a first observation of intensity-dependent effects for such a peculiar beam type. The experimental results are presented and discussed in this paper.

MOPS017	Simulation Studies of Macro-particles Falling into the LHC Proton Beam	634
	F. Zimmermann, T. Baer, M. Giovannozzi, E.B. Holzer, E. Nebot Del Busto, A. Nordt, M. Sapinski CERN, Geneva, Switzerland N. Fuster Valencia University, Atomic Molecular and Nuclear Physics Department, Valencia, Spain Z. Yang EPFL, Lausanne, Switzerland
	We report updated simulations on the interaction of macro-particles falling from the top of the vacuum chamber into the circulating LHC proton beam. The path and charge state of micron size micro-particles are computed together with the resulting beam losses, which – if high enough - can lead to the local quench of SC magnets. The simulated time evolution of the beam loss is compared with observations in order to constrain some macro-particle parameters. We also discuss the possibility of a "multiple crossing" by the same macro-particle, the effect of a strong dipole field, and the dependence of peak loss rate and loss duration on beam current and on beam size.

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.

MOPS021	Beam Dynamics of a Compact SC Isochronous Cyclotron - Preliminary Study of Central Region*	643
	J.X. Zhang, T.A. Antaya, R.E. Block MIT/PSFC, Cambridge, Massachusetts, USA
	Funding: Pennsylvania State University ARL S11-07 and N00024-02-D-6604 US Defense Threat Reduction Agency A compact high field superconducting isochronous cyclotron, Megatron (K250), is designed as a proof-of-principle for a single stage high power proton accelerator. This cyclotron is to accelerate proton to a final energy of 250 MeV with two 45° Dees with a radius ~40 cm. By employing a 20 mA external ECR proton source, the injected proton beam currents at high brightness are foreseen. Using phase selection in the center, a fully magnetized elliptical pole, low energy gain per turn, a precise relation between momentum and radius at large radius are expected. Two goals, a) to use this relationship to develop multi-turn extraction with passive elements only, to achieve a high external proton beam intensity (~1 mA); and b) to see if it is possible to achieve a high extraction efficiency (> 99%) without single turn extraction, with an energy spread \|DE/E\| ~0.1%. The RF acceleration is on the first harmonic with ωrf=ω0~64 MHz. Superconductor coils will provide a central field of B0 = 4.3 T and a peak hill field of 6.6 T. The general beam dynamics studies will be performed. Precise central field design including space charge effect will be shown in the presentation.

THOBA01	Electron Cloud Observations in LHC	2862
	G. Rumolo, G. Arduini, V. Baglin, H. Bartosik, P. Baudrenghien, N. Biancacci, G. Bregliozzi, S.D. Claudet, R. De Maria, J. Esteban Muller, M. Favier, C. Hansen, W. Höfle, J.M. Jimenez, V. Kain, E. Koukovini, G. Lanza, K.S.B. Li, G.H.I. Maury Cuna, E. Métral, G. Papotti, T. Pieloni, F. Roncarolo, B. Salvant, E.N. Shaposhnikova, R.J. Steinhagen, L.J. Tavian, D. Valuch, W. Venturini Delsolaro, F. Zimmermann CERN, Geneva, Switzerland C.M. Bhat Fermilab, Batavia, USA U. Iriso CELLS-ALBA Synchrotron, Cerdanyola del Vallès, Spain N. Mounet, C. Zannini EPFL, Lausanne, Switzerland
	Operation of LHC with bunch trains different spacings has revealed the formation of an electron cloud inside the machine. The main observations of electron cloud build-up are the pressure rise measured at the vacuum gauges in the warm regions, as well as the increase of the beam screen temperature in the cold regions due to an additional heat load. The effects of the electron cloud were also visible as a strong instability and emittance growth affecting the last bunches of longer trains, which could be improved running with higher chromaticity and/or larger transverse emittances. A summary of the 2010 and 2011 observations and measurements and a comparison with existing models will be presented. The efficiency of scrubbing and scrubbing strategies to improve the machine running performance will be also briefly discussed.
	Slides THOBA01 [2.911 MB]

FRXAA01	Theory of Microwave Instability and Coherent Synchrotron Radiation in Electron Storage Rings	3774
	Y. Cai SLAC, Menlo Park, California, USA
	Funding: This work was supported by Department of Energy Contract No. DE-AC02-76SF00515. Bursting of coherent synchrotron radiation has been observed and in fact used to generate THz radiation in many electron storage rings. In order to understand and control the bursting, we return to the study of the microwave instability. In this talk, we will report on the theoretical understanding, including recent developments, of the microwave instability in electron storage rings. The historical progress of the theories will be surveyed, starting from the dispersion relation of coasting beams, to the work of Sacherer on a bunched beam, and ending with the Oide and Yokoya method of discretization. This theoretical survey will be supplemented with key experimental results over the years. Finally, we will describe the recent theoretical development of utilizing the Laguerre polynomials in the presence of potential-well distortion. This self-consistent method will be applied to study the microwave instability driven by commonly known impedances, including that of coherent synchrotron radiation.
	Slides FRXAA01 [0.948 MB]