IPAC2011 - List of Authors (Bruce, R.)

Paper	Title	Page
MOPO011	The First 1 1/2 Years of TOTEM Roman Pot Operation at LHC	502
	M. Deile, G.H. Antchev, R.W. Assmann, I. Atanassov, V. Avati, J. Baechler, R. Bruce, M. Dupont, K. Eggert, B. Farnham, J. Kaspar, F. Lucas Rodríguez, J. Morant, H. Niewiadomski, X. Pons, E. Radermacher, S. Ravat, F. Ravotti, S. Redaelli, G. Ruggiero, H. Sabba, M. Sapinski, W. Snoeys, G. Valentino, D. Wollmann CERN, Geneva, Switzerland R. Appleby UMAN, Manchester, United Kingdom
	Since the LHC running season 2010, the TOTEM Roman Pots (RPs) are fully operational and serve for collecting elastic and diffractive proton-proton scattering data. Like for other moveable devices approaching the high intensity LHC beams, a reliable and precise control of the RP position is critical to machine protection. After a review of the RP movement control and position interlock system, the crucial task of alignment will be discussed.

TUPS026	Specification of New Vacuum Chambers for the LHC Experimental Interactions	1584
	R. Veness, R.W. Assmann, A. Ball, A. Behrens, C. Bracco, G. Bregliozzi, R. Bruce, H. Burkhardt, G. Corti, M.A. Gallilee, M. Giovannozzi, B. Goddard, D. Mergelkuhl, E. Métral, M. Nessi, W. Riegler, J. Wenninger CERN, Geneva, Switzerland N. Mounet, B. Salvant EPFL, Lausanne, Switzerland
	The apertures for the vacuum chambers at the interaction points inside the LHC experiments are key both to the safe operation of the LHC machine and to obtaining the best physics performance from the experiments. Following the successful startup of the LHC physics programme the ALICE, ATLAS and CMS experiments have launched projects to improve physics performance by adding detector layers closer to the beam. To achieve this they have requested smaller aperture vacuum chambers to be installed. The first periods of LHC operation have yielded much information both on the performance of the LHC and the stability and alignment of the experiments. In this paper, the new information relating to the aperture of these chambers is presented and a summary is made of analysis of parameters required to safely reduce the vacuum chambers apertures for the high-luminosity experiments ATLAS and CMS.

TUPS037	Preliminary Assessment of Beam Impact Consequences on LHC Collimators	1617
	M. Cauchi, R.W. Assmann, A. Bertarelli, R. Bruce, F. Carra, A. Dallocchio, D. Deboy, N. Mariani, A. Rossi, N.J. Sammut CERN, Geneva, Switzerland M. Cauchi, P. Mollicone UoM, Msida, Malta L. Lari IFIC, Valencia, Spain
	The correct functioning of the LHC collimation system is crucial to attain the desired LHC luminosity performance. However, the requirements to handle high intensity beams can be demanding. In this respect, the robustness of the collimators plays an important role. An accident which causes the proton beam to hit a collimator might result in severe beam-induced damage and, in some cases, replacement of the collimator, with consequent downtime for the machine. In this paper, several case studies representing different realistic beam impact scenarios are shown. A preliminary analysis of the thermal response of tertiary collimators to beam impact is presented, from which the most critical cases can be identified. Such work will also help to give an initial insight on the operational constraints of the LHC by taking into account all relevant collimator damage limits.

TUPZ006	Aperture Determination in the LHC Based on an Emittance Blowup Technique with Collimator Position Scan	1810
	R.W. Assmann, R. Bruce, M. Giovannozzi, G.J. Müller, S. Redaelli, F. Schmidt, R. Tomás, J. Wenninger, D. Wollmann CERN, Geneva, Switzerland M. Alabau IFIC, Valencia, Spain
	A new method to determine the LHC aperture was proposed. The new component is a collimator scan technique that refers the globally measured aperture limit to the shadow of the primary collimator, expressed in σs of rms beam size. As a by-product the BLM response to beam loss is quantified. The method is described and LHC measurement results are presented.

TUPZ007	First Ion Collimation Commissioning Results at the LHC	1813
	G. Bellodi, R.W. Assmann, R. Bruce, M. Cauchi, J.M. Jowett, G. Valentino, D. Wollmann CERN, Geneva, Switzerland
	First commissioning of the LHC Pb ion beams to 1.38 A TeV energy was successfully achieved in November 2010. Ion collimation has been predicted to be less efficient than for protons at the LHC, because of the complexity of the physical processes involved: nuclear fragmentation and electromagnetic dissociation in the primary collimators creating fragments with a wide range of Z/A ratios, that are not intercepted by the secondary collimators but lost in the dispersion suppressor sections of the ring. In this article we present first comparisons of measured loss maps with theoretical predictions from simulation runs with the ICOSIM code. An extrapolation to define the ultimate intensity limit for Pb beams is attempted. The scope of possible improvements in collimation efficiency coming from the installation of new collimators in the cold dispersion suppressors and combined betatron and momentum cleaning is also explored.

TUPZ011	LHC Collimation with a Reduced Beam Pipe Radius in ATLAS	1822
	R. Bruce, R.W. Assmann CERN, Geneva, Switzerland
	Based on SixTrack simulations, we investigate the effect from collimation of a reduced beam pipe in the ATLAS experiment in the LHC. Several running scenarios are studied with range of different beam pipe radii and in each case we conclude on the minimum allowed aperture, which does not cause beam losses inside the detectors.

TUPZ012	Machine-induced Showers entering the ATLAS and CMS Detectors in the LHC	1825
	R. Bruce, R.W. Assmann, V. Boccone, H. Burkhardt, F. Cerutti, A. Ferrari, M. Huhtinen, W. Kozanecki, Y.I. Levinsen, A. Mereghetti, A. Rossi, Th. Weiler CERN, Geneva, Switzerland N.V. Mokhov Fermilab, Batavia, USA
	One source of experimental background in the LHC is showers induced by particles hitting the upstream collimators or particles that have been scattered on the residual gas. We estimate the flux and distribution of particles entering the ATLAS and CMS detectors through FLUKA simulations originating from tertiary collimator hits and inelastic beam-gas interactions. Comparisons to MARS results are also presented.

TUPZ013	Calculation Method for Safe Beta* in the LHC	1828
	R. Bruce, R.W. Assmann, W. Herr, D. Wollmann CERN, Geneva, Switzerland
	One way of increasing the peak luminosity in the LHC is to decrease the beam size at the interaction points by squeezing to smaller values of beta. The LHC is now in a regime where safety and stability determines the limit in beta, as opposed to traditional optics limits. In this paper, we derive a calculation model to determine the safe beta-values based on collimator settings and operational stability of the LHC. This model was used to calculate the settings for the LHC run in 2011. It was found that beta could be decreased from 3.5 m to 1.5 m, which has now successfully been put into operation.

TUPZ017	Luminosity and Beam Parameter Evolution for Lead Ion Beams in the LHC	1840
	J.M. Jowett, R. Bruce, T. Mertens CERN, Geneva, Switzerland
	Heavy ion beams in the LHC are subject to strong blow-up and debunching effects from intra-beam scattering and luminosity-driven beam losses. The large nuclear charge is at the origin of these effects, both in the cross sections for simple Coulomb scattering and the ultraperipheral interactions occurring in the collisions. We compare predictions from our models with data on luminosity, beam size and intensity evolution from the first heavy ion run of the LHC. This analysis has to take account of the varying capabilities of the LHC beam instrumentation between injection and collision energies.

THPZ026	Collimation Dependent Beam Lifetime and Loss Rates in the LHC	3744
	D. Wollmann, R.W. Assmann, R. Bruce, F. Burkart, M. Cauchi, D. Deboy, S. Redaelli, A. Rossi, G. Valentino CERN, Geneva, Switzerland
	The four primary collimators in each LHC beam define the smallest aperture. Particles with high betatron amplitudes or momentum offset will therefore hit first a primary collimator. The instantaneous particle loss rate at primary collimators is an important measure for the global lifetime of the beams and a major ingredient to identify collimation induced performance limitations in the LHC. These loss rates have been measured during a number of LHC fills, featuring both "good" fills with high luminosity and "bad" fills with beam instabilities. The beam lifetime at the collimators was then calculated from this data for different cases. The results are presented and interpreted within this paper.

THPZ027	First Beam Results for a Collimator with In-jaw Beam Position Monitors	3747
	D. Wollmann, O. Aberle, R.W. Assmann, A. Bertarelli, C.B. Boccard, R. Bruce, F. Burkart, M. Cauchi, A. Dallocchio, D. Deboy, M. Gasior, O.R. Jones, S. Redaelli, A. Rossi, G. Valentino CERN, Geneva, Switzerland
	With more than 100 collimators the LHC has the most complex collimation system ever installed in an accelerator. The beam-based setup time of the system was a non-negligible factor during the commissioning of the LHC. In addition if the particle orbit at a collimator goes out of tolerance, this collimator needs to be setup again. To reduce the required setup time for the collimation system and to obtain the tight tolerances required for the LHC operation with small beta* and high beam energy, a new collimator design is being developed that integrates a beam position monitor (BPM) into the jaws of the collimator. A prototype of such a phase-II LHC collimator was installed in the SPS at CERN for the 2010 run. In this paper we present the first experimental results from the beam tests performed.

THPZ029	Principles for Generation of Time-dependent Collimator Settings during the LHC Cycle	3753
	R. Bruce, R.W. Assmann, S. Redaelli CERN, Geneva, Switzerland
	The settings of the LHC collimators have to be changed during the cycle of injection, ramp and squeeze to account for variations in the orbit, beam size and normalized distance to the beam center. We discuss the principles for how the settings are calculated and show a software tool that computes them as time-dependent functions from beam-based data and theoretical optics models.

THPZ030	Halo Scrapings with Collimators in the LHC	3756
	F. Burkart, R.W. Assmann, R. Bruce, M. Cauchi, D. Deboy, S. Redaelli, A. Rossi, G. Valentino, D. Wollmann CERN, Geneva, Switzerland L. Lari IFIC, Valencia, Spain
	The population of the beam halo has been measured in the LHC with beam scraping experiments. Primary collimators of the LHC collimation system were used to scrape the beam halo at different statuses of the machine (injection, top energy, separated and colliding beams). In addition these measurements were used to calibrate the beam loss monitor signals to loss rates at the primary collimators. Within this paper the halo scraping method, the measured halo distribution and the calibration factors are presented and compared to theoretical predictions.

THPZ035	Comparison of LHC Collimation Setups with Manual and Semi-automatic Collimator Alignment	3771
	G. Valentino, R.W. Assmann, R. Bruce, F. Burkart, M. Cauchi, D. Deboy, S. Redaelli, A. Rossi, N.J. Sammut, D. Wollmann CERN, Geneva, Switzerland G. Valentino University of Malta, Information and Communication Technology, Msida, Malta
	The LHC collimation system beam-based alignment procedure has recently been upgraded to a semi-automatic process in order to increase its efficiency. In this paper, we describe the parameters used to measure the accuracy, stability and performance of the beam-based alignment of the LHC collimation system. This is followed by a comparison of the results at 450 GeV and 3.5 TeV with (1) a manual alignment and (2) with the results for semi-automatic alignment.

Paper

Title

Page

The First 1 1/2 Years of TOTEM Roman Pot Operation at LHC

502

M. Deile, G.H. Antchev, R.W. Assmann, I. Atanassov, V. Avati, J. Baechler, R. Bruce, M. Dupont, K. Eggert, B. Farnham, J. Kaspar, F. Lucas Rodríguez, J. Morant, H. Niewiadomski, X. Pons, E. Radermacher, S. Ravat, F. Ravotti, S. Redaelli, G. Ruggiero, H. Sabba, M. Sapinski, W. Snoeys, G. Valentino, D. Wollmann
CERN, Geneva, Switzerland
R. Appleby
UMAN, Manchester, United Kingdom

Since the LHC running season 2010, the TOTEM Roman Pots (RPs) are fully operational and serve for collecting elastic and diffractive proton-proton scattering data. Like for other moveable devices approaching the high intensity LHC beams, a reliable and precise control of the RP position is critical to machine protection. After a review of the RP movement control and position interlock system, the crucial task of alignment will be discussed.

TUPS026

Specification of New Vacuum Chambers for the LHC Experimental Interactions

1584

R. Veness, R.W. Assmann, A. Ball, A. Behrens, C. Bracco, G. Bregliozzi, R. Bruce, H. Burkhardt, G. Corti, M.A. Gallilee, M. Giovannozzi, B. Goddard, D. Mergelkuhl, E. Métral, M. Nessi, W. Riegler, J. Wenninger
CERN, Geneva, Switzerland
N. Mounet, B. Salvant
EPFL, Lausanne, Switzerland

The apertures for the vacuum chambers at the interaction points inside the LHC experiments are key both to the safe operation of the LHC machine and to obtaining the best physics performance from the experiments. Following the successful startup of the LHC physics programme the ALICE, ATLAS and CMS experiments have launched projects to improve physics performance by adding detector layers closer to the beam. To achieve this they have requested smaller aperture vacuum chambers to be installed. The first periods of LHC operation have yielded much information both on the performance of the LHC and the stability and alignment of the experiments. In this paper, the new information relating to the aperture of these chambers is presented and a summary is made of analysis of parameters required to safely reduce the vacuum chambers apertures for the high-luminosity experiments ATLAS and CMS.

TUPS037

Preliminary Assessment of Beam Impact Consequences on LHC Collimators

1617

M. Cauchi, R.W. Assmann, A. Bertarelli, R. Bruce, F. Carra, A. Dallocchio, D. Deboy, N. Mariani, A. Rossi, N.J. Sammut
CERN, Geneva, Switzerland
M. Cauchi, P. Mollicone
UoM, Msida, Malta
L. Lari
IFIC, Valencia, Spain

The correct functioning of the LHC collimation system is crucial to attain the desired LHC luminosity performance. However, the requirements to handle high intensity beams can be demanding. In this respect, the robustness of the collimators plays an important role. An accident which causes the proton beam to hit a collimator might result in severe beam-induced damage and, in some cases, replacement of the collimator, with consequent downtime for the machine. In this paper, several case studies representing different realistic beam impact scenarios are shown. A preliminary analysis of the thermal response of tertiary collimators to beam impact is presented, from which the most critical cases can be identified. Such work will also help to give an initial insight on the operational constraints of the LHC by taking into account all relevant collimator damage limits.

TUPZ006

Aperture Determination in the LHC Based on an Emittance Blowup Technique with Collimator Position Scan

1810

R.W. Assmann, R. Bruce, M. Giovannozzi, G.J. Müller, S. Redaelli, F. Schmidt, R. Tomás, J. Wenninger, D. Wollmann
CERN, Geneva, Switzerland
M. Alabau
IFIC, Valencia, Spain

A new method to determine the LHC aperture was proposed. The new component is a collimator scan technique that refers the globally measured aperture limit to the shadow of the primary collimator, expressed in σs of rms beam size. As a by-product the BLM response to beam loss is quantified. The method is described and LHC measurement results are presented.

TUPZ007

First Ion Collimation Commissioning Results at the LHC

1813

G. Bellodi, R.W. Assmann, R. Bruce, M. Cauchi, J.M. Jowett, G. Valentino, D. Wollmann
CERN, Geneva, Switzerland

First commissioning of the LHC Pb ion beams to 1.38 A TeV energy was successfully achieved in November 2010. Ion collimation has been predicted to be less efficient than for protons at the LHC, because of the complexity of the physical processes involved: nuclear fragmentation and electromagnetic dissociation in the primary collimators creating fragments with a wide range of Z/A ratios, that are not intercepted by the secondary collimators but lost in the dispersion suppressor sections of the ring. In this article we present first comparisons of measured loss maps with theoretical predictions from simulation runs with the ICOSIM code. An extrapolation to define the ultimate intensity limit for Pb beams is attempted. The scope of possible improvements in collimation efficiency coming from the installation of new collimators in the cold dispersion suppressors and combined betatron and momentum cleaning is also explored.

TUPZ011

LHC Collimation with a Reduced Beam Pipe Radius in ATLAS

1822

R. Bruce, R.W. Assmann
CERN, Geneva, Switzerland

Based on SixTrack simulations, we investigate the effect from collimation of a reduced beam pipe in the ATLAS experiment in the LHC. Several running scenarios are studied with range of different beam pipe radii and in each case we conclude on the minimum allowed aperture, which does not cause beam losses inside the detectors.

TUPZ012

Machine-induced Showers entering the ATLAS and CMS Detectors in the LHC

1825

R. Bruce, R.W. Assmann, V. Boccone, H. Burkhardt, F. Cerutti, A. Ferrari, M. Huhtinen, W. Kozanecki, Y.I. Levinsen, A. Mereghetti, A. Rossi, Th. Weiler
CERN, Geneva, Switzerland
N.V. Mokhov
Fermilab, Batavia, USA

One source of experimental background in the LHC is showers induced by particles hitting the upstream collimators or particles that have been scattered on the residual gas. We estimate the flux and distribution of particles entering the ATLAS and CMS detectors through FLUKA simulations originating from tertiary collimator hits and inelastic beam-gas interactions. Comparisons to MARS results are also presented.

TUPZ013

Calculation Method for Safe Beta* in the LHC

1828

R. Bruce, R.W. Assmann, W. Herr, D. Wollmann
CERN, Geneva, Switzerland

One way of increasing the peak luminosity in the LHC is to decrease the beam size at the interaction points by squeezing to smaller values of beta*. The LHC is now in a regime where safety and stability determines the limit in beta*, as opposed to traditional optics limits. In this paper, we derive a calculation model to determine the safe beta*-values based on collimator settings and operational stability of the LHC. This model was used to calculate the settings for the LHC run in 2011. It was found that beta* could be decreased from 3.5 m to 1.5 m, which has now successfully been put into operation.

TUPZ017

Luminosity and Beam Parameter Evolution for Lead Ion Beams in the LHC

1840

J.M. Jowett, R. Bruce, T. Mertens
CERN, Geneva, Switzerland

Heavy ion beams in the LHC are subject to strong blow-up and debunching effects from intra-beam scattering and luminosity-driven beam losses. The large nuclear charge is at the origin of these effects, both in the cross sections for simple Coulomb scattering and the ultraperipheral interactions occurring in the collisions. We compare predictions from our models with data on luminosity, beam size and intensity evolution from the first heavy ion run of the LHC. This analysis has to take account of the varying capabilities of the LHC beam instrumentation between injection and collision energies.

THPZ026

Collimation Dependent Beam Lifetime and Loss Rates in the LHC

3744

D. Wollmann, R.W. Assmann, R. Bruce, F. Burkart, M. Cauchi, D. Deboy, S. Redaelli, A. Rossi, G. Valentino
CERN, Geneva, Switzerland

The four primary collimators in each LHC beam define the smallest aperture. Particles with high betatron amplitudes or momentum offset will therefore hit first a primary collimator. The instantaneous particle loss rate at primary collimators is an important measure for the global lifetime of the beams and a major ingredient to identify collimation induced performance limitations in the LHC. These loss rates have been measured during a number of LHC fills, featuring both "good" fills with high luminosity and "bad" fills with beam instabilities. The beam lifetime at the collimators was then calculated from this data for different cases. The results are presented and interpreted within this paper.

THPZ027

First Beam Results for a Collimator with In-jaw Beam Position Monitors

3747

D. Wollmann, O. Aberle, R.W. Assmann, A. Bertarelli, C.B. Boccard, R. Bruce, F. Burkart, M. Cauchi, A. Dallocchio, D. Deboy, M. Gasior, O.R. Jones, S. Redaelli, A. Rossi, G. Valentino
CERN, Geneva, Switzerland

With more than 100 collimators the LHC has the most complex collimation system ever installed in an accelerator. The beam-based setup time of the system was a non-negligible factor during the commissioning of the LHC. In addition if the particle orbit at a collimator goes out of tolerance, this collimator needs to be setup again. To reduce the required setup time for the collimation system and to obtain the tight tolerances required for the LHC operation with small beta* and high beam energy, a new collimator design is being developed that integrates a beam position monitor (BPM) into the jaws of the collimator. A prototype of such a phase-II LHC collimator was installed in the SPS at CERN for the 2010 run. In this paper we present the first experimental results from the beam tests performed.

THPZ029

Principles for Generation of Time-dependent Collimator Settings during the LHC Cycle

3753

R. Bruce, R.W. Assmann, S. Redaelli
CERN, Geneva, Switzerland

The settings of the LHC collimators have to be changed during the cycle of injection, ramp and squeeze to account for variations in the orbit, beam size and normalized distance to the beam center. We discuss the principles for how the settings are calculated and show a software tool that computes them as time-dependent functions from beam-based data and theoretical optics models.

THPZ030

Halo Scrapings with Collimators in the LHC

3756

F. Burkart, R.W. Assmann, R. Bruce, M. Cauchi, D. Deboy, S. Redaelli, A. Rossi, G. Valentino, D. Wollmann
CERN, Geneva, Switzerland
L. Lari
IFIC, Valencia, Spain

The population of the beam halo has been measured in the LHC with beam scraping experiments. Primary collimators of the LHC collimation system were used to scrape the beam halo at different statuses of the machine (injection, top energy, separated and colliding beams). In addition these measurements were used to calibrate the beam loss monitor signals to loss rates at the primary collimators. Within this paper the halo scraping method, the measured halo distribution and the calibration factors are presented and compared to theoretical predictions.

THPZ035

Comparison of LHC Collimation Setups with Manual and Semi-automatic Collimator Alignment

3771

G. Valentino, R.W. Assmann, R. Bruce, F. Burkart, M. Cauchi, D. Deboy, S. Redaelli, A. Rossi, N.J. Sammut, D. Wollmann
CERN, Geneva, Switzerland
G. Valentino
University of Malta, Information and Communication Technology, Msida, Malta

The LHC collimation system beam-based alignment procedure has recently been upgraded to a semi-automatic process in order to increase its efficiency. In this paper, we describe the parameters used to measure the accuracy, stability and performance of the beam-based alignment of the LHC collimation system. This is followed by a comparison of the results at 450 GeV and 3.5 TeV with (1) a manual alignment and (2) with the results for semi-automatic alignment.