IPAC2016 - Classification: 05 Beam Dynamics and Electromagnetic Fields / D05 Coherent and Incoherent Instabilities

Paper	Title	Page
TUOAB03	Transverse Coherent Instabilities in Storage Rings with Harmonic Cavities	1061
	F.J. Cullinan, R. Nagaoka SOLEIL, Gif-sur-Yvette, France G. Skripka, P.F. Tavares MAX IV Laboratory, Lund University, Lund, Sweden
	Many current and future synchrotron light sources employ harmonic cavities to lengthen the electron bunches in order to reduce the emittance dilution caused by intrabeam scattering. In some cases, the harmonic cavities may be tuned to fulfill the flat potential condition. For this condition, a large increase in the threshold currents of transverse coupled-bunch instabilities has been predicted and recently, the physical content behind this stabilization has been better understood. With this in mind, an investigation is made into the effectiveness of harmonic cavities for different machines. Frequency domain computations employing Laclare's eigenvalue method have been used to investigate the influence of several machine parameters and the results are presented.
	Slides TUOAB03 [14.037 MB]
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TUPOR001	Lifetime Improvements with a Harmonic RF System for the ESRF EBS	1644
	N. Carmignani, L. Farvacque, J. Jacob, S.M. Liuzzo, B. Nash, T.P. Perron, P. Raimondi, R. Versteegen, S.M. White ESRF, Grenoble, France
	A third-harmonic RF system to increase the Touschek lifetime is under study for the European Synchrotron Radiation Facility (ESRF) Extremely Brilliant Source (EBS) storage ring, in particular for modes with high current per bunch. Multi-particle simulations have been done to study the bunch lengthening and shape in presence of inductive impedance and a third-harmonic RF system.
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TUPOR002	Residual Ion Dynamics in ThomX Electron Storage Ring	1648
	A.R. Gamelin, C. Bruni LAL, Orsay, France
	Funding: Work is supported by ANR-10-EQPX-51, by grants from Région Ile-de-France, IN2P3 and Pheniics Doctoral School. ThomX is a compact Compton Backscattering Source (CBS) which is being built in Orsay, France. Ions produced from residual gas in the storage ring can induce several instabilities. However the electron beam stability is crucial to attain the nominal performances foreseen. In order to prevent instabilities ion cleaning is considered. Complete studies of the beam effect on the ions have been undertaken. It shows that there are preferential ion accumulation points depending on the storage ring lattice. This paper will detail the ion longitudinal and transverse dynamics considering the optics of ThomX storage ring.
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TUPOR003	CSR-Driven Longitudinal Single Bunch Instability with Negative Momentum Compaction Factor	1651
	P. Kuske HZB, Berlin, Germany
	Acceptable agreement is found between experimental results obtained at the Metrology Light Source (MLS) operated with negative momentum compaction factor, α, and theoretical estimates of the CSR-driven threshold currents. Theoretical instability thresholds are estimated by numerically solving the Vlasov-Fokker-Planck equation and/or by multi particle tracking and taking into account the shielded CSR-interaction. Some of the issues with the calculations, the determination of the theoretical thresholds as well as the derivation of a general scaling law will be presented
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TUPOR004	Calculation of Transverse Coupled Bunch Instabilities in Electron Storage Rings Driven By Quadrupole Higher Order Modes	1655
	M. Ruprecht, P. Goslawski, M. Ries, G. Wüstefeld HZB, Berlin, Germany
	This paper presents a formula that estimates the growth rate of a transverse coupled bunch instability driven by quadrupole higher order modes (HOMs) in electron storage rings. Thus far, quadrupole HOMs are usually ignored in HOM driven instability studies for electron storage rings due to their weak nature compared to the lower orders. However, they may become relevant when high gradient SC multi-cell cavities with their potentially strong impedance spectrum are operated at high currents in a third generation or future synchrotron light source. An example is BESSY VSR, a scheme where 1.7 ps and 15 ps long bunches (rms) can be stored simultaneously in the BESSY II storage ring[]. With the presented formula, instability thresholds are discussed for a recent BESSY VSR cavity model and different beam parameters. A. Jankowiak, J. Knobloch, P. Goslawski, and N. Neumann, eds., BESSY VSR - Technical Design Study, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 2015.
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TUPOR005	A Parallelized Vlasov-Fokker-Planck-Solver for Desktop PCs	1658
	P. Schönfeldt, M. Brosi, A.-S. Müller, J.L. Steinmann KIT, Karlsruhe, Germany
	In order simulate the dynamics of an electron bunch due to the self-interaction with its own coherent synchrotron radiation it is a well established method to numerically solve the Vlasov-Fokker-Planck equation. In this paper we present a new, modularly extensible program that uses OpenCL to massively parallelize the computation, allowing a standard desktop PC to work with appropriate accuracy and yield reliable results within minutes. We provide numerical stability studies of over a huge parameter range and comparisons of our numerical results to other techniques.
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TUPOR008	Effect of the Various Impedances on Longitudinal Beam Stability in the CERN SPS	1666
	A. Lasheen, T. Argyropoulos, J. Repond, E.N. Shaposhnikova CERN, Geneva, Switzerland
	The High Luminosity (HL)-LHC project at CERN aims at a luminosity increase by a factor ten and one of the necessary ingredients is doubling the bunch intensity to 2.4x10¹¹ ppb for beams with 25 ns bunch spacing. Many improvements are already foreseen in the frame of the LHC Injector Upgrade (LIU) project, but probably this intensity would still not be reachable in the SPS due to longitudinal instabilities. Recently a lot of effort went into finding the impedance sources of the instabilities. Particle simulations based on the latest SPS impedance model are now able to reproduce the measured instability thresholds and were used to determine the most critical impedance sources by removing them one by one from the model. It was found that impedance of vacuum flanges and of the already damped 630 MHz HOM of the main RF system gave for 72 bunches the comparable intensity thresholds. Possible intensity gains are defined for realistic impedance modifications and for various beam configurations (number of bunches, longitudinal emittances) and RF programs (single and double RF). The results of this study are used as a guideline for planning of a new campaign of the SPS impedance reduction.
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TUPOR010	Simulation of Instability at Transition Energy with a New Impedance Model for CERN PS	1674
	N. Wang IHEP, Beijing, People's Republic of China S. Aumon, N. Biancacci, M. Migliorati, G. Sterbini, N. Wang CERN, Geneva, Switzerland M. Migliorati INFN-Roma1, Rome, Italy S. Persichelli University of Rome La Sapienza, Rome, Italy
	Instabilities driven by the transverse impedance are proven to be one of the limitations for the high intensity reach of the CERN PS. Since several years, fast single bunch vertical instability at transition energy has been observed with the high intensity bunch serving the neu-tron Time-of-Flight facility (n-ToF). In order to better understand the instability mechanism, a dedicated meas-urement campaign took place. The results were compared with macro-particle simulations with PyHEADTAIL based on the new impedance model developed for the PS. Instability threshold and growth rate for different longitu-dinal emittances and beam intensities were studied.
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TUPOR011	Study of Microwave Instability for SLS-2	1678
	H.S. Xu, P. Craievich, M.M. Dehler, L. Stingelin PSI, Villigen PSI, Switzerland
	An ultra-low emittance electron storage ring is under development for the Upgrade of Swiss Light Source (SLS-2). An antechamber scheme consisting of round beam channel with 10 mm inner radius is considered to accommodate the required strong quadrupole and sextupole magnets, achieve the ultra-high vacuum, and absorb the undesired synchrotron radiation. However, the small size of vacuum chamber increases the susceptibility of the beam to the impedance induced collective instabilities. We will present the preliminary study of the microwave instability for SLS-2 storage ring considering the longitudinal Resistive-Wall (RW) impedance due to three different options for the beam chamber. The microwave instability thresholds are calculated under the conditions of two possible RF frequencies (100 MHz and 500 MHz) and three different materials (aluminum, copper, and stainless steel). The influences of third-harmonic cavities are also studied.
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TUPOR012	THz Coherent Synchrotron Radiation from Ultra-low Alpha Operating Mode at Diamond Light Source	1682
	T. Chanwattana, M. Atay, R. Bartolini JAI, Oxford, United Kingdom R. Bartolini, G. Cinque, M. Frogley, E. Koukovini-Platia, I.P.S. Martin DLS, Oxfordshire, United Kingdom
	Diamond Light Source is regularly operated in low-alpha mode to provide THz coherent synchrotron radiation (CSR) and short X-ray pulses for users. In order to maintain the wide frequency range of the coherent radiation whilst improving the signal to noise ratio, an ultra-low alpha mode has been considered to shorten the bunch length even further. In order to study this mode, the analysis of single bunch dynamics resulting from a variety of wakefield sources has been investigated using a single bunch multiparticle tracking code. These results are compared with measurements recorded using a Fourier transform infrared (FTIR) interferometer on the MIRIAM beam-line at Diamond.
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TUPOR021	Incoherent Vertical Emittance Growth from Electron Cloud at CesrTA	1707
	S. Poprocki, J.A. Crittenden, S.N. Hearth, J.D. Perrin, D. L. Rubin, S. Wang Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: Work supported by the US National Science Foundation PHY-1416318, PHY-0734867, and PHY-1002467, and the U.S. Department of Energy DE-FC02-08ER41538 We report on measurements of electron cloud (EC) induced tune shifts and emittance growth at the Cornell Electron-Positron Storage Ring Test Accelerator (CesrTA) with comparison to tracking simulation predictions. The simulations are based on a weak-strong model of the interaction of the positron beam (weak) with the electron cloud (strong), using electric fields computed with established EC buildup simulation codes (ECLOUD). Experiments were performed with 2.1 GeV positrons in a 30 bunch train with 14 ns bunch spacing and 9 mm bunch length, plus a witness bunch at varying distance from the train to probe the cloud as it decays. Measurements of the horizontal and vertical coherent tune shifts and horizontal and vertical bunch size were obtained for a range of train and witness bunch currents, and compared to simulations.
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Paper

Title

Page

Transverse Coherent Instabilities in Storage Rings with Harmonic Cavities

1061

F.J. Cullinan, R. Nagaoka
SOLEIL, Gif-sur-Yvette, France
G. Skripka, P.F. Tavares
MAX IV Laboratory, Lund University, Lund, Sweden

Many current and future synchrotron light sources employ harmonic cavities to lengthen the electron bunches in order to reduce the emittance dilution caused by intrabeam scattering. In some cases, the harmonic cavities may be tuned to fulfill the flat potential condition. For this condition, a large increase in the threshold currents of transverse coupled-bunch instabilities has been predicted and recently, the physical content behind this stabilization has been better understood. With this in mind, an investigation is made into the effectiveness of harmonic cavities for different machines. Frequency domain computations employing Laclare's eigenvalue method have been used to investigate the influence of several machine parameters and the results are presented.

Slides TUOAB03 [14.037 MB]

Export •

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

TUPOR001

Lifetime Improvements with a Harmonic RF System for the ESRF EBS

1644

N. Carmignani, L. Farvacque, J. Jacob, S.M. Liuzzo, B. Nash, T.P. Perron, P. Raimondi, R. Versteegen, S.M. White
ESRF, Grenoble, France

A third-harmonic RF system to increase the Touschek lifetime is under study for the European Synchrotron Radiation Facility (ESRF) Extremely Brilliant Source (EBS) storage ring, in particular for modes with high current per bunch. Multi-particle simulations have been done to study the bunch lengthening and shape in presence of inductive impedance and a third-harmonic RF system.

Export •

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

TUPOR002

Residual Ion Dynamics in ThomX Electron Storage Ring

1648

A.R. Gamelin, C. Bruni
LAL, Orsay, France

Funding: Work is supported by ANR-10-EQPX-51, by grants from Région Ile-de-France, IN2P3 and Pheniics Doctoral School.
ThomX is a compact Compton Backscattering Source (CBS) which is being built in Orsay, France. Ions produced from residual gas in the storage ring can induce several instabilities. However the electron beam stability is crucial to attain the nominal performances foreseen. In order to prevent instabilities ion cleaning is considered. Complete studies of the beam effect on the ions have been undertaken. It shows that there are preferential ion accumulation points depending on the storage ring lattice. This paper will detail the ion longitudinal and transverse dynamics considering the optics of ThomX storage ring.

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TUPOR003

CSR-Driven Longitudinal Single Bunch Instability with Negative Momentum Compaction Factor

1651

P. Kuske
HZB, Berlin, Germany

Acceptable agreement is found between experimental results obtained at the Metrology Light Source (MLS) operated with negative momentum compaction factor, α, and theoretical estimates of the CSR-driven threshold currents. Theoretical instability thresholds are estimated by numerically solving the Vlasov-Fokker-Planck equation and/or by multi particle tracking and taking into account the shielded CSR-interaction. Some of the issues with the calculations, the determination of the theoretical thresholds as well as the derivation of a general scaling law will be presented

Export •

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

TUPOR004

Calculation of Transverse Coupled Bunch Instabilities in Electron Storage Rings Driven By Quadrupole Higher Order Modes

1655

M. Ruprecht, P. Goslawski, M. Ries, G. Wüstefeld
HZB, Berlin, Germany

This paper presents a formula that estimates the growth rate of a transverse coupled bunch instability driven by quadrupole higher order modes (HOMs) in electron storage rings. Thus far, quadrupole HOMs are usually ignored in HOM driven instability studies for electron storage rings due to their weak nature compared to the lower orders. However, they may become relevant when high gradient SC multi-cell cavities with their potentially strong impedance spectrum are operated at high currents in a third generation or future synchrotron light source. An example is BESSY VSR, a scheme where 1.7 ps and 15 ps long bunches (rms) can be stored simultaneously in the BESSY II storage ring[*]. With the presented formula, instability thresholds are discussed for a recent BESSY VSR cavity model and different beam parameters.
* A. Jankowiak, J. Knobloch, P. Goslawski, and N. Neumann, eds., BESSY VSR - Technical Design Study, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 2015.

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TUPOR005

A Parallelized Vlasov-Fokker-Planck-Solver for Desktop PCs

1658

P. Schönfeldt, M. Brosi, A.-S. Müller, J.L. Steinmann
KIT, Karlsruhe, Germany

In order simulate the dynamics of an electron bunch due to the self-interaction with its own coherent synchrotron radiation it is a well established method to numerically solve the Vlasov-Fokker-Planck equation. In this paper we present a new, modularly extensible program that uses OpenCL to massively parallelize the computation, allowing a standard desktop PC to work with appropriate accuracy and yield reliable results within minutes. We provide numerical stability studies of over a huge parameter range and comparisons of our numerical results to other techniques.

Export •

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

TUPOR008

Effect of the Various Impedances on Longitudinal Beam Stability in the CERN SPS

1666

A. Lasheen, T. Argyropoulos, J. Repond, E.N. Shaposhnikova
CERN, Geneva, Switzerland

The High Luminosity (HL)-LHC project at CERN aims at a luminosity increase by a factor ten and one of the necessary ingredients is doubling the bunch intensity to 2.4x10¹¹ ppb for beams with 25 ns bunch spacing. Many improvements are already foreseen in the frame of the LHC Injector Upgrade (LIU) project, but probably this intensity would still not be reachable in the SPS due to longitudinal instabilities. Recently a lot of effort went into finding the impedance sources of the instabilities. Particle simulations based on the latest SPS impedance model are now able to reproduce the measured instability thresholds and were used to determine the most critical impedance sources by removing them one by one from the model. It was found that impedance of vacuum flanges and of the already damped 630 MHz HOM of the main RF system gave for 72 bunches the comparable intensity thresholds. Possible intensity gains are defined for realistic impedance modifications and for various beam configurations (number of bunches, longitudinal emittances) and RF programs (single and double RF). The results of this study are used as a guideline for planning of a new campaign of the SPS impedance reduction.

Export •

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

TUPOR010

Simulation of Instability at Transition Energy with a New Impedance Model for CERN PS

1674

N. Wang
IHEP, Beijing, People's Republic of China
S. Aumon, N. Biancacci, M. Migliorati, G. Sterbini, N. Wang
CERN, Geneva, Switzerland
M. Migliorati
INFN-Roma1, Rome, Italy
S. Persichelli
University of Rome La Sapienza, Rome, Italy

Instabilities driven by the transverse impedance are proven to be one of the limitations for the high intensity reach of the CERN PS. Since several years, fast single bunch vertical instability at transition energy has been observed with the high intensity bunch serving the neu-tron Time-of-Flight facility (n-ToF). In order to better understand the instability mechanism, a dedicated meas-urement campaign took place. The results were compared with macro-particle simulations with PyHEADTAIL based on the new impedance model developed for the PS. Instability threshold and growth rate for different longitu-dinal emittances and beam intensities were studied.

Export •

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

TUPOR011

Study of Microwave Instability for SLS-2

1678

H.S. Xu, P. Craievich, M.M. Dehler, L. Stingelin
PSI, Villigen PSI, Switzerland

An ultra-low emittance electron storage ring is under development for the Upgrade of Swiss Light Source (SLS-2). An antechamber scheme consisting of round beam channel with 10 mm inner radius is considered to accommodate the required strong quadrupole and sextupole magnets, achieve the ultra-high vacuum, and absorb the undesired synchrotron radiation. However, the small size of vacuum chamber increases the susceptibility of the beam to the impedance induced collective instabilities. We will present the preliminary study of the microwave instability for SLS-2 storage ring considering the longitudinal Resistive-Wall (RW) impedance due to three different options for the beam chamber. The microwave instability thresholds are calculated under the conditions of two possible RF frequencies (100 MHz and 500 MHz) and three different materials (aluminum, copper, and stainless steel). The influences of third-harmonic cavities are also studied.

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TUPOR012

THz Coherent Synchrotron Radiation from Ultra-low Alpha Operating Mode at Diamond Light Source

1682

T. Chanwattana, M. Atay, R. Bartolini
JAI, Oxford, United Kingdom
R. Bartolini, G. Cinque, M. Frogley, E. Koukovini-Platia, I.P.S. Martin
DLS, Oxfordshire, United Kingdom

Diamond Light Source is regularly operated in low-alpha mode to provide THz coherent synchrotron radiation (CSR) and short X-ray pulses for users. In order to maintain the wide frequency range of the coherent radiation whilst improving the signal to noise ratio, an ultra-low alpha mode has been considered to shorten the bunch length even further. In order to study this mode, the analysis of single bunch dynamics resulting from a variety of wakefield sources has been investigated using a single bunch multiparticle tracking code. These results are compared with measurements recorded using a Fourier transform infrared (FTIR) interferometer on the MIRIAM beam-line at Diamond.

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TUPOR021

Incoherent Vertical Emittance Growth from Electron Cloud at CesrTA

1707

S. Poprocki, J.A. Crittenden, S.N. Hearth, J.D. Perrin, D. L. Rubin, S. Wang
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: Work supported by the US National Science Foundation PHY-1416318, PHY-0734867, and PHY-1002467, and the U.S. Department of Energy DE-FC02-08ER41538
We report on measurements of electron cloud (EC) induced tune shifts and emittance growth at the Cornell Electron-Positron Storage Ring Test Accelerator (CesrTA) with comparison to tracking simulation predictions. The simulations are based on a weak-strong model of the interaction of the positron beam (weak) with the electron cloud (strong), using electric fields computed with established EC buildup simulation codes (ECLOUD). Experiments were performed with 2.1 GeV positrons in a 30 bunch train with 14 ns bunch spacing and 9 mm bunch length, plus a witness bunch at varying distance from the train to probe the cloud as it decays. Measurements of the horizontal and vertical coherent tune shifts and horizontal and vertical bunch size were obtained for a range of train and witness bunch currents, and compared to simulations.

Export •

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