IPAC2014 - List of Authors (Esteban Muller, J. F.)

Paper	Title	Page
TUPME027	Analysis of the Electron Cloud Observations with 25 ns Bunch Spacing at the LHC	1410
	G. Iadarola Naples University Federico II, Science and Technology Pole, Napoli, Italy G. Arduini, V. Baglin, D. Banfi, H. Bartosik, S.D. Claudet, C.O. Domínguez, J.F. Esteban Müller, G. Iadarola, T. Pieloni, G. Rumolo, E.N. Shaposhnikova, L.J. Tavian, C. Zannini, F. Zimmermann CERN, Geneva, Switzerland
	Electron Cloud (EC) effects have been identified as a major performance limitation for the Large Hadron Collider (LHC) when operating with the nominal bunch spacing of 25 ns. During the LHC Run 1 (2010 - 2013) the luminosity production mainly used beams with 50 ns spacing, while 25 ns beams were only employed for short periods in 2011 and 2012 for test purposes. On these occasions, observables such as pressure rise, heat load in the cold sections as well as clear signatures on bunch-by-bunch emittance blow up, particle loss and energy loss indicated the presence of an EC in a large portion of the LHC. The analysis of the recorded data, together with EC build up simulations, has led to a significant improvement of our understanding of the EC effect in the different components of the LHC. Studies were carried out both at injection energy (450 GeV) and at top energy (4 TeV) aiming at determining the energy dependence of the EC formation and its impact on the quality of the proton beam.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME027
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TUPME028	Flat Bunches in the LHC	1413
	E.N. Shaposhnikova, T. Argyropoulos, P. Baudrenghien, J.F. Esteban Müller, T. Mastoridis, G. Papotti, B. Salvant, H. Timko CERN, Geneva, Switzerland C.M. Bhat, A.V. Burov Fermilab, Batavia, Illinois, USA
	A high-harmonic RF system that could serve multiple purposes was proposed for the LHC. Possible applications of the second harmonic RF system include beam stabilisation in the longitudinal plane in the absence of wide-band longitudinal feedback and reduction of bunch peak line-density. Apart from other useful features, flat bunches are expected to produce less beam-induced heating at frequencies below 1 GHz, the frequency region critical for some LHC equipment. The latter, however, can also be achieved by de-populating the bunch centre. This was demonstrated during the dedicated machine development session in the LHC using RF phase modulation. In this paper the results of tests with single bunches and nominal LHC beams are presented and the possible use of this technique in LHC operation is discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME028
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TUPME029	Identification of High-frequency Resonant Impedance in the CERN SPS	1416
	E.N. Shaposhnikova, T. Argyropoulos, T. Bohl, J.V. Campelo, F. Caspers, J.F. Esteban Müller, A. Lasheen, B. Salvant, H. Timko CERN, Geneva, Switzerland
	The spectrum of long bunches injected into the ring with RF switched off has been used in the SPS in the past to probe the longitudinal coupling impedance. After a large campaign of shielding of 800 inter-magnet vacuum ports in 1999 - 2001, the microwave instability threshold was significantly increased and the high-frequency spectrum of the beam became practically flat, apart from a prominent peak at around 1.4 GHz. As corresponding high-frequency impedance could potentially lead to microwave instability of high intensity bunches observed now at high energies in the SPS, a search of the source of this impedance was launched. Using a combination of impedance simulations and measurements, vacuum flanges that are present in a large quantity in the machine have been identified as a main source of impedance at this frequency. Particle simulations based on the SPS impedance model, which includes this previously unknown impedance, are able to reproduce the characteristics of the bunch spectrum and amplitude growth rates and hence, confirm that the impedance of the vacuum flanges is responsible for the observed spectral peak.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME029
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TUPRI056	Beam Measurements of the LHC Impedance and Validation of the Impedance Model	1698
	J.F. Esteban Müller, T. Argyropoulos, T. Bohl, N. Mounet, E.N. Shaposhnikova, H. Timko CERN, Geneva, Switzerland
	Different measurements of the longitudinal impedance of the LHC done with single bunches with various intensities and longitudinal emittances during measurement sessions in 2011-2012 are compared with particle simulations based on the existing LHC impedance model. The very low reactive impedance of the LHC, with Im(Z/n) around 0.1 Ohm, is not easy to measure. The most sensitive observation is the loss of Landau damping during acceleration, which shows at which energy bunches become unstable depending on their parameters. In addition, the synchrotron frequency shift due to the reactive impedance was estimated following two methods. Firstly, it was obtained from the peak-detected Schottky spectrum. Secondly, a sine modulation in the RF phase was applied to the bunches with different intensities and the modulation frequency was scanned. In both cases, the synchrotron frequency shift was of the order of the measurement precision.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI056
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THPPA00	EPS-AG Prize d) Presentation	2837
	J.F. Esteban Müller EPFL, Lausanne, Switzerland J.F. Esteban Müller CERN, Geneva, Switzerland
	EPS-AG Prize d) Presentation. The Prize d) winner will present the work for which the prize is awarded, on the basis of the judging by the EPS-AG Prizes Selectin Committee.
	Slides THPPA00 [3.432 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPPA00
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THPME174	High-accuracy Diagnostic Tool for Electron Cloud Observation in the LHC based on Synchronous Phase Measurements	3677
SUSPSNE068	use link to see paper's listing under its alternate paper code
	J.F. Esteban Müller, P. Baudrenghien, T. Mastoridis, E.N. Shaposhnikova, D. Valuch CERN, Geneva, Switzerland
	Electron cloud effects such as heat load in the cryogenic system, pressure rise and beam instabilities are among the main limitations for the LHC operation with 25 ns spaced bunches. A new observation tool was developed to monitor the e-cloud activity and has been successfully used in the LHC during Run 1 (2010-2012). The power loss of each bunch due to the e-cloud can be estimated using very precise bunch-by-bunch measurement of the synchronous phase shift. In order to achieve the required accuracy, corrections for reflection in the cables and some systematic errors need to be applied followed by a post-processing of the measurements. Results show clearly the e-cloud build-up along the bunch trains and its evolution during each LHC fill as well as from fill to fill. Measurements during the 2012 LHC scrubbing run reveal a progressive reduction in the e-cloud activity and therefore a decrease in the secondary electron yield (SEY). The total beam power loss can be computed as a sum of the contributions from all bunches and compared with the heat load deposited in the cryogenic system. The plan to use this method in the LHC operation is also presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPME174
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Analysis of the Electron Cloud Observations with 25 ns Bunch Spacing at the LHC

1410

G. Iadarola
Naples University Federico II, Science and Technology Pole, Napoli, Italy
G. Arduini, V. Baglin, D. Banfi, H. Bartosik, S.D. Claudet, C.O. Domínguez, J.F. Esteban Müller, G. Iadarola, T. Pieloni, G. Rumolo, E.N. Shaposhnikova, L.J. Tavian, C. Zannini, F. Zimmermann
CERN, Geneva, Switzerland

Electron Cloud (EC) effects have been identified as a major performance limitation for the Large Hadron Collider (LHC) when operating with the nominal bunch spacing of 25 ns. During the LHC Run 1 (2010 - 2013) the luminosity production mainly used beams with 50 ns spacing, while 25 ns beams were only employed for short periods in 2011 and 2012 for test purposes. On these occasions, observables such as pressure rise, heat load in the cold sections as well as clear signatures on bunch-by-bunch emittance blow up, particle loss and energy loss indicated the presence of an EC in a large portion of the LHC. The analysis of the recorded data, together with EC build up simulations, has led to a significant improvement of our understanding of the EC effect in the different components of the LHC. Studies were carried out both at injection energy (450 GeV) and at top energy (4 TeV) aiming at determining the energy dependence of the EC formation and its impact on the quality of the proton beam.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME027

Export •

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

TUPME028

Flat Bunches in the LHC

1413

E.N. Shaposhnikova, T. Argyropoulos, P. Baudrenghien, J.F. Esteban Müller, T. Mastoridis, G. Papotti, B. Salvant, H. Timko
CERN, Geneva, Switzerland
C.M. Bhat, A.V. Burov
Fermilab, Batavia, Illinois, USA

A high-harmonic RF system that could serve multiple purposes was proposed for the LHC. Possible applications of the second harmonic RF system include beam stabilisation in the longitudinal plane in the absence of wide-band longitudinal feedback and reduction of bunch peak line-density. Apart from other useful features, flat bunches are expected to produce less beam-induced heating at frequencies below 1 GHz, the frequency region critical for some LHC equipment. The latter, however, can also be achieved by de-populating the bunch centre. This was demonstrated during the dedicated machine development session in the LHC using RF phase modulation. In this paper the results of tests with single bunches and nominal LHC beams are presented and the possible use of this technique in LHC operation is discussed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME028

Export •

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

TUPME029

Identification of High-frequency Resonant Impedance in the CERN SPS

1416

E.N. Shaposhnikova, T. Argyropoulos, T. Bohl, J.V. Campelo, F. Caspers, J.F. Esteban Müller, A. Lasheen, B. Salvant, H. Timko
CERN, Geneva, Switzerland

The spectrum of long bunches injected into the ring with RF switched off has been used in the SPS in the past to probe the longitudinal coupling impedance. After a large campaign of shielding of 800 inter-magnet vacuum ports in 1999 - 2001, the microwave instability threshold was significantly increased and the high-frequency spectrum of the beam became practically flat, apart from a prominent peak at around 1.4 GHz. As corresponding high-frequency impedance could potentially lead to microwave instability of high intensity bunches observed now at high energies in the SPS, a search of the source of this impedance was launched. Using a combination of impedance simulations and measurements, vacuum flanges that are present in a large quantity in the machine have been identified as a main source of impedance at this frequency. Particle simulations based on the SPS impedance model, which includes this previously unknown impedance, are able to reproduce the characteristics of the bunch spectrum and amplitude growth rates and hence, confirm that the impedance of the vacuum flanges is responsible for the observed spectral peak.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME029

Export •

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

TUPRI056

Beam Measurements of the LHC Impedance and Validation of the Impedance Model

1698

J.F. Esteban Müller, T. Argyropoulos, T. Bohl, N. Mounet, E.N. Shaposhnikova, H. Timko
CERN, Geneva, Switzerland

Different measurements of the longitudinal impedance of the LHC done with single bunches with various intensities and longitudinal emittances during measurement sessions in 2011-2012 are compared with particle simulations based on the existing LHC impedance model. The very low reactive impedance of the LHC, with Im(Z/n) around 0.1 Ohm, is not easy to measure. The most sensitive observation is the loss of Landau damping during acceleration, which shows at which energy bunches become unstable depending on their parameters. In addition, the synchrotron frequency shift due to the reactive impedance was estimated following two methods. Firstly, it was obtained from the peak-detected Schottky spectrum. Secondly, a sine modulation in the RF phase was applied to the bunches with different intensities and the modulation frequency was scanned. In both cases, the synchrotron frequency shift was of the order of the measurement precision.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI056

Export •

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

THPPA00

EPS-AG Prize d) Presentation

2837

J.F. Esteban Müller
EPFL, Lausanne, Switzerland
J.F. Esteban Müller
CERN, Geneva, Switzerland

EPS-AG Prize d) Presentation. The Prize d) winner will present the work for which the prize is awarded, on the basis of the judging by the EPS-AG Prizes Selectin Committee.

Slides THPPA00 [3.432 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPPA00

Export •

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

THPME174

High-accuracy Diagnostic Tool for Electron Cloud Observation in the LHC based on Synchronous Phase Measurements

3677

SUSPSNE068

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

J.F. Esteban Müller, P. Baudrenghien, T. Mastoridis, E.N. Shaposhnikova, D. Valuch
CERN, Geneva, Switzerland

Electron cloud effects such as heat load in the cryogenic system, pressure rise and beam instabilities are among the main limitations for the LHC operation with 25 ns spaced bunches. A new observation tool was developed to monitor the e-cloud activity and has been successfully used in the LHC during Run 1 (2010-2012). The power loss of each bunch due to the e-cloud can be estimated using very precise bunch-by-bunch measurement of the synchronous phase shift. In order to achieve the required accuracy, corrections for reflection in the cables and some systematic errors need to be applied followed by a post-processing of the measurements. Results show clearly the e-cloud build-up along the bunch trains and its evolution during each LHC fill as well as from fill to fill. Measurements during the 2012 LHC scrubbing run reveal a progressive reduction in the e-cloud activity and therefore a decrease in the secondary electron yield (SEY). The total beam power loss can be computed as a sum of the contributions from all bunches and compared with the heat load deposited in the cryogenic system. The plan to use this method in the LHC operation is also presented.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPME174

Export •

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