IPAC2016 - Classification: 05 Beam Dynamics and Electromagnetic Fields / D04 Beam Coupling Impedance - Theory, Simulations, Measurements, Code Developments

Paper	Title	Page
MOPMY003	Transient Beam Loading Effects in RF Systems in JLEIC	518
	H. Wang, J. Guo, R.A. Rimmer, S. Wang JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The pulsed electron bunch trains generated from the Continuous Electron Beam Accelerator Facility (CEBAF) linac to inject into the proposed Jefferson Lab Electron Ion Collider (JLEIC) e-ring will produce transient beam loading effects in the Superconducting Radio Frequency (SRF) systems that, if not mitigated, could cause unacceptably large beam energy deviation in the injection capture, exceed the energy acceptance of CEBAF's recirculating arc. In the electron storage ring, the beam abort or ion clearing gaps or uneven bucket filling can cause large beam phase transients in the (S)RF cavity control systems and even beam loss due to Robinson instability. We have first analyzed the beam stability criteria in steady state and estimate the transient effect in Feedforward and Feedback RF controls. Initial analytical models for these effects are shown for the design of the JLEIC e-ring from 3GeV to 12GeV.
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MOPOR002	Impedance Simulations and Measurements for ThomX Storage Ring	586
	A.R. Gamelin, C. Bruni, V. Chaumat, D. Le Guidec, P. Lepercq, R. Marie 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 at LAL, Orsay, France. ThomX ring has a short circumference of 18 m and a design energy of 50 MeV. Due to the low energy of the beam and in order to avoid beam degradation it is important to evaluate the ring components impedance. A CST Particle Studio impedance simulation of the different components of the ring (BPM, bellows, optical chamber, etc.) is under way. It will be followed by a bench measurement of the longitudinal and transverse impedance using the coaxial wire method. This paper will detail the preliminary results of the ThomX storage ring impedance simulations and the measurement principle we will use.
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MOPOR003	Simulation Studies and Measurements of Beam Instabilities Caused by the Kicker Impedance at High Intensities in the 3-GeV RCS of J-PARC	589
	P.K. Saha, H. Harada, N. Hayashi, H. Hotchi, M. Kinsho, M. Nomura, Y. Shobuda, F. Tamura, N. Tani, Y. Watanabe, M. Yamamoto JAEA/J-PARC, Tokai-mura, Japan
	The transverse impedance of the extraction kickers is a significant beam instability source in the 3-GeV Rapid Cycling Synchrotron of J-PARC. ORBIT code was developed for space charge and beam instability simulations by successfully introducing realistic time dependent machine parameters. The beam instability at high intensities, especially at the designed 1 MW beam power was found be very critical. As there was no practical measure yet to reduce the kicker impedance, a detail simulation studies were done in order to determine realistic machine parameters to suppress the beam instability. The simulation results were found to be very consistent with measurements to successfully accomplish 1 MW beam power. The simulation and beam study results in detail are presented in this paper.
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MOPOR005	Longitudinal Wakefields in the Undulator Section of SXFEL User Facility	595
SUPSS052	use link to see paper's listing under its alternate paper code
	M. Song, H.X. Deng, C. Feng, D. Huang, B. Liu, D. Wang SINAP, Shanghai, People's Republic of China
	Shanghai soft x-ray free electron laser (SXFEL) user facility based on multi-stage seeded-FEL and self-amplified spontaneous emission (SASE) is recently proposed, which is aiming at generating 4-2nm fully-coherent, high-brightness FEL pulse. In this paper, the wakefields arise from the resistive wall and surface roughness in the vacuum chamber is obtained by theoretical models. And the computations of geometric wakefields are carried out using ABCI. According to the tracked beam profile, the overall wakefields in the undulator section of SXFEL user facility are presented. K. Bane, G. Stupakov, SLAC-PUB-15951, May 2014. ** ABCI website: http://abci.kek.jp/abci.htm
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MOPOR007	Local Impedance Measurements at ALBA from Turn-by-Turn Acquisition	598
	M. Carlà, G. Benedetti, T.F.G. Günzel, U. Iriso, Z. Martí ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain
	A transverse impedance source manifests itself, among other ways, by producing a small defocusing kick which depends on the beam bunch charge. By repeating optics measurements for different bunch charges, it is possible to disentangle the contribution produced by each impedance source from the dominating focusing effects given by the machine optics. But hunting for such faint defocusing effects poses strong requirements on the precision and sensibility of the measurements, and slow machine drifts or different thermal conditions shall be avoided. In this report, we present a novel method to assess in a fast and precise manner machine optics for different bunch charges using BPM turn-by-turn data and hybrid filling patterns. Finally, measurements for different ALBA machine components like scrapers and In-vacuum undulators are compared with simulation results.
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MOPOR008	Beam Induced RF Heating in LHC in 2015	602
	B. Salvant, O. Aberle, M. Albert, R. Alemany-Fernandez, G. Arduini, J. Baechler, M.J. Barnes, P. Baudrenghien, O.E. Berrig, N. Biancacci, G. Bregliozzi, J.V. Campelo, F. Carra, F. Caspers, P. Chiggiato, A. Danisi, H.A. Day, M. Deile, D. Druzhkin, J.F. Esteban Müller, S. Jakobsen, J. Kuczerowski, A. Lechner, R. Losito, A. Masi, N. Minafra, E. Métral, A.A. Nosych, A. Perillo Marcone, D. Perini, S. Redaelli, F. Roncarolo, G. Rumolo, E.N. Shaposhnikova, J.A. Uythoven, C. Vollinger, A.J. Välimaa, N. Wang, M. Wendt, J. Wenninger, C. Zannini CERN, Geneva, Switzerland M. Bozzo INFN Genova, Genova, Italy J.F. Esteban Müller EPFL, Lausanne, Switzerland N. Wang IHEP, Beijing, People's Republic of China
	Following the recurrent beam induced RF issues that perturbed LHC operation during LHC Run 1, a series of actions were put in place to minimize the risk that similar issues would occur in LHC Run 2: longitudinal impedance reduction campaign and/or improvement of cooling for equipment that were problematic or at the limit during Run 1, stringent constraints enforced on new equipment that would be installed in the machine, tests to control the bunch length and longitudinal distribution, additional monitoring of temperature, new monitoring tools and warning chains. This contribution reports the outcome of these actions, both successes as well as shortcomings, and details the lessons learnt for the future runs.
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MOPOR009	The HL-LHC Impedance Model and Aspects of Beam Stability	606
	N. Biancacci, K.S.B. Li, E. Métral, B. Salvant CERN, Geneva, Switzerland
	Funding: Research supported by the High Luminosity LHC project The LHC upgrade to the HLLHC foresees new challenging operational scenarios from the beam dynamics point of view. In order to ensure good machine operation and performance, the machine impedance, among other possible sources of instabilities like beam-beam and electron cloud, needs to be carefully quantified profiting also from the current LHC operation. In this work we present the HLLHC impedance model mainly focusing on the contribution of low-impedance collimators and crab cavities: the first reduces the broad-band impedance baseline thanks to the higher jaw material conductivity, the second increases the machine luminosity at the price of increasing the coupled bunch stabilizing octupole current threshold. Other elements like the injection protection absorber (TDI) will be also discussed.
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MOPOR010	Impedance Measurements and Simulations on the TCTP and TDI LHC Collimators	610
	N. Biancacci, F. Caspers, A. Grudiev, J. Kuczerowski, I. Lamas Garcia, A. Lechner, E. Métral, A. Passarelli, A. Perillo Marcone, B. Salvant, J.A. Uythoven CERN, Geneva, Switzerland O. Frasciello, M. Zobov INFN/LNF, Frascati (Roma), Italy A. Mostacci Rome University La Sapienza, Roma, Italy N. Mounet EPFL, Lausanne, Switzerland
	The LHC collimation system is a critical element for the safe operation of the LHC machine and is subject to continuous performance monitoring, hardware upgrade and optimization. In this work we will address the impact on impedance of the upgrades performed on the TDI injection protection collimator, where the absorber material has been changed to mitigate the device heating observed in machine operation, and on selected secondary (TCS) and tertiary (TCT) collimators, where beam position monitors (BPM) have been embedded for faster jaw alignment. Concerning the TDI, we will present the RF measurements performed before and after the upgrade, comparing the result to heating and tune shift beam measurements. For the TCTs, we will study how the higher order modes (HOM) introduced by the BPM addition have been cured by means of ferrite placement in the device. The impedance mitigation campaign has been supported by RF measurements whose results are in good agreement with GdfidL and CST simulations. The presence of undamped low frequency modes is proved not to be detrimental to the safe LHC operation.
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MOPOR011	Impedance Localization Measurements using AC Dipoles in the LHC	614
	N. Biancacci, L.R. Carver, G. Papotti, T. Persson, B. Salvant, R. Tomás CERN, Geneva, Switzerland
	The knowledge of the LHC impedance is of primary importance to predict the machine performance and allow for the HL-LHC upgrade. The developed impedance model can be benchmarked with beam measurements in order to assess its validity and limit. This is routinely done, for example, moving the LHC collimator jaws and measuring the induced tune shift. In order to localize possible unknown impedance sources, the variation of phase advance with intensity between beam position monitors can be measured. In this work we will present the impedance localization measurements performed at injection in the LHC using AC dipoles as exciter as well as the underlying theory.
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MOPOR012	Study of the Beam-Cavity Interaction in the PS 10 MHz RF System	618
	G. Favia, H. Damerau, M. Morvillo, C. Rossi CERN, Geneva, Switzerland M. Migliorati University of Rome "La Sapienza", Rome, Italy
	The eleven main accelerating cavities of the Proton Synchrotron (PS) at CERN consist of two ferrite-loaded coaxial λ/4 resonators each. Both resonators oscillate in phase, as their gaps are electrically connected by short bars. They are in addition magnetically coupled via the bias loop used for cavity tuning. The cavities are equipped with a wide-band feedback system, limiting the beam loading, and a further reduction of the beam induced voltage is achieved by relays which short-circuit each half-resonator gap when the cavity is not in use. Asymmetries of the beam induced voltage observed in the two half-cavities indicate that the coupling between the two resonators is not as tight as expected. The total cavity impedance coupling to the beam may be affected differently by the contributions of both resonators. A dedicated measurement campaign with high-intensity proton beam and numerical simulation have been performed to investigate the beam-cavity interaction. This paper reports the result of the study and the work aiming at the development of a model of the system, including the wide-band feedback, which reproduces this interaction.
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MOPOR014	Measurements of the CERN PS Longitudinal Resistive Coupling Impedance	626
	M. Migliorati, N. Biancacci, H. Damerau, G. Sterbini CERN, Geneva, Switzerland M. Migliorati University of Rome "La Sapienza", Rome, Italy M. Migliorati, L. Ventura INFN-Roma1, Rome, Italy S. Persichelli University of Rome La Sapienza, Rome, Italy
	The longitudinal coupling impedance of the CERN PS has been studied in the past years in order to better understand collective effects which could produce beam intensity limitations for the LHC Injectors Upgrade project. By measuring the incoherent quadrupole synchrotron frequency vs beam intensity, the inductive impedance was evaluated and compared with the impedance model obtained by taking into account the contribution of the most important machine devices. In this paper, we present the results of the measurements performed during a dedicated campaign, of the real part of the longitudinal coupling impedance by means of the synchronous phase shift vs beam intensity. The phase shift has been measured by using two different techniques: in one case, we injected in the machine two bunches, one used as a reference with constant intensity, and the second one changing its intensity; in the second case, more conventional, we measured the bunch position with respect to the RF signal of the 40 MHz cavities. The obtained dependence of the synchrotron phase with intensity is then related to the loss factor and the resistive coupling impedance, which is compared to the real part of the PS impedance model.
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MOPOR016	Impedance Study with Single Bunch Beam at Taiwan Photon Source	630
	C.-C. Kuo, P.J. Chou, K.T. Hsu, K.H. Hu, C.C. Liang, C.Y. Liao, Z.K. Liu, H.-J. Tsai, F.H. Tseng NSRRC, Hsinchu, Taiwan
	The impedance at Taiwan Photon Source was investigated. The effects of bunch current such as a tune change, a synchronous phase shift and a bunch lengthening under operation conditions at various stages were measured; the machine impedances were deduced. This report presents the results with insertion devices in various configurations.
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MOPOR018	Single Bunch Instability Studies at Diamond Light Source	637
	E. Koukovini-Platia, M. Apollonio, R. Bartolini, R.T. Fielder, I.P.S. Martin DLS, Oxfordshire, United Kingdom R. Bartolini JAI, Oxford, United Kingdom
	Single bunch instability thresholds, the associated coherent tune shifts and the bunch lengthening have been studied at Diamond light source for nominal optics. Measurements were taken under different settings of chromaticity, radio-frequency (RF) voltage and aperture of the insertion devices (IDs). The macro-particle code sbtrack was used to evaluate the instability thresholds and bunch lengthening where different impedance contributions are taken into account such as the resistive wall impedance, a broad-band resonator model and inductive impedance for the longitudinal plane. A comparison of simulation using the developed model impedance with measurements is shown for all cases.
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Paper

Title

Page

Transient Beam Loading Effects in RF Systems in JLEIC

518

H. Wang, J. Guo, R.A. Rimmer, S. Wang
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The pulsed electron bunch trains generated from the Continuous Electron Beam Accelerator Facility (CEBAF) linac to inject into the proposed Jefferson Lab Electron Ion Collider (JLEIC) e-ring will produce transient beam loading effects in the Superconducting Radio Frequency (SRF) systems that, if not mitigated, could cause unacceptably large beam energy deviation in the injection capture, exceed the energy acceptance of CEBAF's recirculating arc. In the electron storage ring, the beam abort or ion clearing gaps or uneven bucket filling can cause large beam phase transients in the (S)RF cavity control systems and even beam loss due to Robinson instability. We have first analyzed the beam stability criteria in steady state and estimate the transient effect in Feedforward and Feedback RF controls. Initial analytical models for these effects are shown for the design of the JLEIC e-ring from 3GeV to 12GeV.

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

MOPOR002

Impedance Simulations and Measurements for ThomX Storage Ring

586

A.R. Gamelin, C. Bruni, V. Chaumat, D. Le Guidec, P. Lepercq, R. Marie
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 at LAL, Orsay, France. ThomX ring has a short circumference of 18 m and a design energy of 50 MeV. Due to the low energy of the beam and in order to avoid beam degradation it is important to evaluate the ring components impedance. A CST Particle Studio impedance simulation of the different components of the ring (BPM, bellows, optical chamber, etc.) is under way. It will be followed by a bench measurement of the longitudinal and transverse impedance using the coaxial wire method. This paper will detail the preliminary results of the ThomX storage ring impedance simulations and the measurement principle we will use.

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

MOPOR003

Simulation Studies and Measurements of Beam Instabilities Caused by the Kicker Impedance at High Intensities in the 3-GeV RCS of J-PARC

589

P.K. Saha, H. Harada, N. Hayashi, H. Hotchi, M. Kinsho, M. Nomura, Y. Shobuda, F. Tamura, N. Tani, Y. Watanabe, M. Yamamoto
JAEA/J-PARC, Tokai-mura, Japan

The transverse impedance of the extraction kickers is a significant beam instability source in the 3-GeV Rapid Cycling Synchrotron of J-PARC. ORBIT code was developed for space charge and beam instability simulations by successfully introducing realistic time dependent machine parameters. The beam instability at high intensities, especially at the designed 1 MW beam power was found be very critical. As there was no practical measure yet to reduce the kicker impedance, a detail simulation studies were done in order to determine realistic machine parameters to suppress the beam instability. The simulation results were found to be very consistent with measurements to successfully accomplish 1 MW beam power. The simulation and beam study results in detail are presented in this paper.

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

MOPOR005

Longitudinal Wakefields in the Undulator Section of SXFEL User Facility

595

SUPSS052

use link to see paper's listing under its alternate paper code

M. Song, H.X. Deng, C. Feng, D. Huang, B. Liu, D. Wang
SINAP, Shanghai, People's Republic of China

Shanghai soft x-ray free electron laser (SXFEL) user facility based on multi-stage seeded-FEL and self-amplified spontaneous emission (SASE) is recently proposed, which is aiming at generating 4-2nm fully-coherent, high-brightness FEL pulse. In this paper, the wakefields arise from the resistive wall and surface roughness in the vacuum chamber is obtained by theoretical models*. And the computations of geometric wakefields are carried out using ABCI**. According to the tracked beam profile, the overall wakefields in the undulator section of SXFEL user facility are presented.
* K. Bane, G. Stupakov, SLAC-PUB-15951, May 2014.
** ABCI website: http://abci.kek.jp/abci.htm

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MOPOR007

Local Impedance Measurements at ALBA from Turn-by-Turn Acquisition

598

M. Carlà, G. Benedetti, T.F.G. Günzel, U. Iriso, Z. Martí
ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain

A transverse impedance source manifests itself, among other ways, by producing a small defocusing kick which depends on the beam bunch charge. By repeating optics measurements for different bunch charges, it is possible to disentangle the contribution produced by each impedance source from the dominating focusing effects given by the machine optics. But hunting for such faint defocusing effects poses strong requirements on the precision and sensibility of the measurements, and slow machine drifts or different thermal conditions shall be avoided. In this report, we present a novel method to assess in a fast and precise manner machine optics for different bunch charges using BPM turn-by-turn data and hybrid filling patterns. Finally, measurements for different ALBA machine components like scrapers and In-vacuum undulators are compared with simulation results.

Export •

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

MOPOR008

Beam Induced RF Heating in LHC in 2015

602

B. Salvant, O. Aberle, M. Albert, R. Alemany-Fernandez, G. Arduini, J. Baechler, M.J. Barnes, P. Baudrenghien, O.E. Berrig, N. Biancacci, G. Bregliozzi, J.V. Campelo, F. Carra, F. Caspers, P. Chiggiato, A. Danisi, H.A. Day, M. Deile, D. Druzhkin, J.F. Esteban Müller, S. Jakobsen, J. Kuczerowski, A. Lechner, R. Losito, A. Masi, N. Minafra, E. Métral, A.A. Nosych, A. Perillo Marcone, D. Perini, S. Redaelli, F. Roncarolo, G. Rumolo, E.N. Shaposhnikova, J.A. Uythoven, C. Vollinger, A.J. Välimaa, N. Wang, M. Wendt, J. Wenninger, C. Zannini
CERN, Geneva, Switzerland
M. Bozzo
INFN Genova, Genova, Italy
J.F. Esteban Müller
EPFL, Lausanne, Switzerland
N. Wang
IHEP, Beijing, People's Republic of China

Following the recurrent beam induced RF issues that perturbed LHC operation during LHC Run 1, a series of actions were put in place to minimize the risk that similar issues would occur in LHC Run 2: longitudinal impedance reduction campaign and/or improvement of cooling for equipment that were problematic or at the limit during Run 1, stringent constraints enforced on new equipment that would be installed in the machine, tests to control the bunch length and longitudinal distribution, additional monitoring of temperature, new monitoring tools and warning chains. This contribution reports the outcome of these actions, both successes as well as shortcomings, and details the lessons learnt for the future runs.

Export •

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

MOPOR009

The HL-LHC Impedance Model and Aspects of Beam Stability

606

N. Biancacci, K.S.B. Li, E. Métral, B. Salvant
CERN, Geneva, Switzerland

Funding: Research supported by the High Luminosity LHC project
The LHC upgrade to the HLLHC foresees new challenging operational scenarios from the beam dynamics point of view. In order to ensure good machine operation and performance, the machine impedance, among other possible sources of instabilities like beam-beam and electron cloud, needs to be carefully quantified profiting also from the current LHC operation. In this work we present the HLLHC impedance model mainly focusing on the contribution of low-impedance collimators and crab cavities: the first reduces the broad-band impedance baseline thanks to the higher jaw material conductivity, the second increases the machine luminosity at the price of increasing the coupled bunch stabilizing octupole current threshold. Other elements like the injection protection absorber (TDI) will be also discussed.

Export •

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

MOPOR010

Impedance Measurements and Simulations on the TCTP and TDI LHC Collimators

610

N. Biancacci, F. Caspers, A. Grudiev, J. Kuczerowski, I. Lamas Garcia, A. Lechner, E. Métral, A. Passarelli, A. Perillo Marcone, B. Salvant, J.A. Uythoven
CERN, Geneva, Switzerland
O. Frasciello, M. Zobov
INFN/LNF, Frascati (Roma), Italy
A. Mostacci
Rome University La Sapienza, Roma, Italy
N. Mounet
EPFL, Lausanne, Switzerland

The LHC collimation system is a critical element for the safe operation of the LHC machine and is subject to continuous performance monitoring, hardware upgrade and optimization. In this work we will address the impact on impedance of the upgrades performed on the TDI injection protection collimator, where the absorber material has been changed to mitigate the device heating observed in machine operation, and on selected secondary (TCS) and tertiary (TCT) collimators, where beam position monitors (BPM) have been embedded for faster jaw alignment. Concerning the TDI, we will present the RF measurements performed before and after the upgrade, comparing the result to heating and tune shift beam measurements. For the TCTs, we will study how the higher order modes (HOM) introduced by the BPM addition have been cured by means of ferrite placement in the device. The impedance mitigation campaign has been supported by RF measurements whose results are in good agreement with GdfidL and CST simulations. The presence of undamped low frequency modes is proved not to be detrimental to the safe LHC operation.

Export •

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

MOPOR011

Impedance Localization Measurements using AC Dipoles in the LHC

614

N. Biancacci, L.R. Carver, G. Papotti, T. Persson, B. Salvant, R. Tomás
CERN, Geneva, Switzerland

The knowledge of the LHC impedance is of primary importance to predict the machine performance and allow for the HL-LHC upgrade. The developed impedance model can be benchmarked with beam measurements in order to assess its validity and limit. This is routinely done, for example, moving the LHC collimator jaws and measuring the induced tune shift. In order to localize possible unknown impedance sources, the variation of phase advance with intensity between beam position monitors can be measured. In this work we will present the impedance localization measurements performed at injection in the LHC using AC dipoles as exciter as well as the underlying theory.

Export •

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

MOPOR012

Study of the Beam-Cavity Interaction in the PS 10 MHz RF System

618

G. Favia, H. Damerau, M. Morvillo, C. Rossi
CERN, Geneva, Switzerland
M. Migliorati
University of Rome "La Sapienza", Rome, Italy

The eleven main accelerating cavities of the Proton Synchrotron (PS) at CERN consist of two ferrite-loaded coaxial λ/4 resonators each. Both resonators oscillate in phase, as their gaps are electrically connected by short bars. They are in addition magnetically coupled via the bias loop used for cavity tuning. The cavities are equipped with a wide-band feedback system, limiting the beam loading, and a further reduction of the beam induced voltage is achieved by relays which short-circuit each half-resonator gap when the cavity is not in use. Asymmetries of the beam induced voltage observed in the two half-cavities indicate that the coupling between the two resonators is not as tight as expected. The total cavity impedance coupling to the beam may be affected differently by the contributions of both resonators. A dedicated measurement campaign with high-intensity proton beam and numerical simulation have been performed to investigate the beam-cavity interaction. This paper reports the result of the study and the work aiming at the development of a model of the system, including the wide-band feedback, which reproduces this interaction.

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

MOPOR014

Measurements of the CERN PS Longitudinal Resistive Coupling Impedance

626

M. Migliorati, N. Biancacci, H. Damerau, G. Sterbini
CERN, Geneva, Switzerland
M. Migliorati
University of Rome "La Sapienza", Rome, Italy
M. Migliorati, L. Ventura
INFN-Roma1, Rome, Italy
S. Persichelli
University of Rome La Sapienza, Rome, Italy

The longitudinal coupling impedance of the CERN PS has been studied in the past years in order to better understand collective effects which could produce beam intensity limitations for the LHC Injectors Upgrade project. By measuring the incoherent quadrupole synchrotron frequency vs beam intensity, the inductive impedance was evaluated and compared with the impedance model obtained by taking into account the contribution of the most important machine devices. In this paper, we present the results of the measurements performed during a dedicated campaign, of the real part of the longitudinal coupling impedance by means of the synchronous phase shift vs beam intensity. The phase shift has been measured by using two different techniques: in one case, we injected in the machine two bunches, one used as a reference with constant intensity, and the second one changing its intensity; in the second case, more conventional, we measured the bunch position with respect to the RF signal of the 40 MHz cavities. The obtained dependence of the synchrotron phase with intensity is then related to the loss factor and the resistive coupling impedance, which is compared to the real part of the PS impedance model.

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MOPOR016

Impedance Study with Single Bunch Beam at Taiwan Photon Source

630

C.-C. Kuo, P.J. Chou, K.T. Hsu, K.H. Hu, C.C. Liang, C.Y. Liao, Z.K. Liu, H.-J. Tsai, F.H. Tseng
NSRRC, Hsinchu, Taiwan

The impedance at Taiwan Photon Source was investigated. The effects of bunch current such as a tune change, a synchronous phase shift and a bunch lengthening under operation conditions at various stages were measured; the machine impedances were deduced. This report presents the results with insertion devices in various configurations.

Export •

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MOPOR018

Single Bunch Instability Studies at Diamond Light Source

637

E. Koukovini-Platia, M. Apollonio, R. Bartolini, R.T. Fielder, I.P.S. Martin
DLS, Oxfordshire, United Kingdom
R. Bartolini
JAI, Oxford, United Kingdom

Single bunch instability thresholds, the associated coherent tune shifts and the bunch lengthening have been studied at Diamond light source for nominal optics. Measurements were taken under different settings of chromaticity, radio-frequency (RF) voltage and aperture of the insertion devices (IDs). The macro-particle code sbtrack was used to evaluate the instability thresholds and bunch lengthening where different impedance contributions are taken into account such as the resistive wall impedance, a broad-band resonator model and inductive impedance for the longitudinal plane. A comparison of simulation using the developed model impedance with measurements is shown for all cases.

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