IPAC2011 - List of Keywords (collimation)

Paper	Title	Other Keywords	Page
MOPS080	Comparison of the Current LHC Collimators and the SLAC Phase 2 Collimator Impedances	impedance, coupling, simulation, cavity	790
	H.A. Day, R.M. Jones UMAN, Manchester, United Kingdom F. Caspers, H.A. Day, E. Métral, B. Salvant CERN, Geneva, Switzerland
	One of the key sources of transverse impedance in the LHC has been the secondary graphite collimators that sit close to the beam at all energies. This limits the stable bunch intensity due to transverse coupled-bunch instabilities and transverse mode coupling instability. To counteract this, new secondary collimators have been proposed for the phase II upgrade of the LHC collimation system. A number of designs based on different jaw materials and mechanical designs have been proposed. A comparison of the beam coupling impedance of these different designs derived from simulations are presented, with reference to the existing phase I secondary collimator design.

TUOAA02	Status of UA9, the Crystal Collimation Experiment in the SPS	ion, proton, simulation, beam-losses	897
	W. Scandale LAL, Orsay, France
	Funding: CERN, IHEP-Protvino, Imperial-College, INFN, JINR-Dubna, LBNL, PNPI-Gartchina, SLAC UA9 was operated in the CERN-SPS for more than two years in view of investigating the feasibility of the halo collimation with bent crystals. Silicon crystals 2 mm long with bending angles of about 150 urad were used as primary collimators. The crystal collimation process was steadily achieved through channeling with high efficiency. The crystal orientation was easily set and optimized with the installed goniometer which has an angular reproducibility of about ± 10 μrad. In channeling orientation, the loss rate of the halo particles interacting with the crystal is reduced by a factor of ten, whilst the residual off-momentum halo escaping from the crystal-collimator area is reduced by a factor five. The crystal channeling efficiency of about 75 % is reasonably consistent with simulations and with single pass data collected in the North Area of the SPS. The accumulated observations, shown in this paper, support our expectation that the coherent deflection of the beam halo by a bent crystal should considerably help in enhancing the collimation efficiency in LHC.
	Slides TUOAA02 [4.297 MB]

TUPS013	Development of the H0 Dump Branch Duct for the Additional Collimation System in J-PARC RCS	septum, shielding, beam-losses, vacuum	1545
	M. Yoshimoto JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
	For the new collimation system in the J-PARC RCS, we have the H0 branch duct installed at the dump septum magnet remodeled. This new branch duct is made of the two kinds of the stainless steels as follows; austenitic stainless steel, SUS316L and ferritic stainless steel, SUS430. In order to research on the property of the SUS430, test ducts were made in various heat-treating condition. In this presentation, we report the design of the new H0 branch duct and the study results with the test ducts.

TUPS032	Overview of EuCARD Accelerator and Material Research at GSI	ion, radiation, heavy-ion, quadrupole	1602
	J. Stadlmann, H. Kollmus, E. Mustafin, N. Pyka, P.J. Spiller, I. Strašík, N.A. Tahir, M. Tomut, C. Trautmann GSI, Darmstadt, Germany L.H.J. Bozyk TU Darmstadt, Darmstadt, Germany
	Funding: EuCARD is co-funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 227579 EuCARD is a joined accelerator R&D initiative funded by the EU. Within this program, GSI Darmstadt is performing R&D on materials for accelerators and collimators in WP8(ColMat). GSI covers prototyping and testing of a cryogenic ion catcher for FAIR's main synchrotron SIS100, simulations and studies on activation of accelerator components e.g. halo collimatiors as well as irradiation experiments on materials foreseen to be used in FAIR accelerators and the LHC upgrade program. Carbon-carbon composites, silicon carbide and copper-diamond composite samples have been irradiated with heavy ions at various GSI beamlines and their radiation induced property changes were characterized. Numerical simulations on the possible damage by LHC and SPS beams to different targets have been performed. Simulations and modelling of activation and long term radiation induced damage to accelerator components have started. A prototype ion catcher has been built and first experiments have been performed in 2011. New collaborations with other institutes and industry in the EuCARD framework have been established and findings of the joined R&D effort influence decisions in the FAIR project and LHC upgrade.

TUPS033	Foil Scattering Loss Mitigation by the Additional Collimation System of J-PARC RCS	injection, vacuum, septum, scattering	1605
	K. Yamamoto, H. Harada, J. Kamiya, Y. Yamazaki, M. Yoshimoto JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
	In the RCS, the significant losses were observed at the branch of H0 dump line and the Beam Position Monitor which was put at the downstream of the H0 dump branch duct. From the beam study, we were certain that these losses were caused by the scattering of the injection and circulating beam at the charge exchange injection foil. In order to mitigate these losses, we started to develop a new collimation system in the H0 branch duct. We presents a overview of this new collimation system.

TUPS035	LHC Collimators with Embedded Beam Position Monitors: A New Advanced Mechanical Design	alignment, pick-up, simulation, radiation	1611
	A. Dallocchio, A. Bertarelli, C.B. Boccard, F. Carra, M. Gasior, L. Gentini, M.A. Timmins CERN, Geneva, Switzerland
	The LHC collimation system, ensuring both functions of beam cleaning and machine protection, is potentially submitted to high-energy beam impacts. Currently the collimators setup is performed by monitoring beam losses generated by the collimator jaws when approaching the particle beam. This procedure is applied to all LHC collimators (almost one hundred), taking several hours, and needs to be repeated if beam settings change significantly. Furthermore, during the beam-based alignment, the LHC tertiary collimators are potentially exposed to abnormal losses entailing possible damage to their tungsten jaws. To improve the efficiency of the machine operation and better control the particle beam a new advanced design embedding Beam Position Monitors (BPM) into the movable collimator jaws has been developed. This paper describes the mechanical design of various types of future collimators with embedded BPMs. Experimental measurements performed on a simplified functional prototype installed in the CERN SPS showed that, thanks to on-board BPMs, the collimator could be precisely, rapidly, and safely aligned and the beam position accurately measured.

TUPS037	Preliminary Assessment of Beam Impact Consequences on LHC Collimators	simulation, proton, controls, beam-losses	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.

TUPS041	Thermo-mechanical Study of a CLIC Bunch Train hitting a Beryllium Energy Spoiler Model	radiation, wakefield, simulation, linac	1629
	J.-L. Fernández-Hernando, D. Angal-Kalinin STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom J. Resta-López IFIC, Valencia, Spain
	A thermo-mechanical study of the impact a CLIC bunch train has over a beryllium energy spoiler has been made. Beryllium has a high electrical and thermal conductivity which together with a large radiation length compared to other metals makes it an optimal candidate for a long tapered design spoiler that will not generate high wakefields, which might degrade the orbit stability and affect the collider luminosity. This paper shows the progress made from the paper presented last year in IPAC 2010. While in the aforementioned paper the study of the temperature and stress was made for the duration of the bunch train this time the study shows the evolution of the stress in the spoiler body 3 microseconds after the bunch train hit.

TUPZ007	First Ion Collimation Commissioning Results at the LHC	ion, betatron, simulation, proton	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	simulation, optics, scattering, background	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	simulation, proton, background, beam-losses	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	luminosity, emittance, optics, injection	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.

WEODA02	Collimation Studies with Hollow Electron Beams	electron, antiproton, gun, proton	1939
	G. Stancari, G. Annala, T.R. Johnson, G.W. Saewert, V.D. Shiltsev, D.A. Still, A. Valishev Fermilab, Batavia, USA
	Funding: Fermi Research Alliance, LLC operates Fermilab under Contract DE-AC02-07CH11359 with the US Department of Energy. This work was partially supported by the US LHC Accelerator Research Program (LARP). Recent experimental studies at the Tevatron collider have shown that magnetically confined hollow electron beams can act as a new kind of collimator for high-intensity beams in storage rings. In a hollow electron beam collimator, electrons enclose the circulating beam. Their electric charge kicks halo particles transversely. If their distribution is axially symmetric, the beam core is unaffected. This device is complementary to conventional two-stage collimation systems: the electron beam can be placed arbitrarily close to the circulating beam; and particle removal is smooth, so that the device is a diffusion enhancer rather than a hard aperture limitation. The concept was tested in the Tevatron collider using a hollow electron gun installed in one of the existing electron lenses. We describe some of the technical aspects of hollow-beam scraping and the results of recent measurements.
	Slides WEODA02 [9.049 MB]

WEPC177	Collimation of High Intensity Ion Beams*	solenoid, ion, ion-source, simulation	2403
	J. Pfister, O. Meusel IAP, Frankfurt am Main, Germany O.K. Kester GSI, Darmstadt, Germany
	Funding: HIC for FAIR Intense ion beams with small phase space occupation (high brilliance) are mandatory to keep beam losses low in high current injector accelerators like those planned for FAIR. The low energy beam transport from the ion source towards the linac has to keep the emittance growth low and has to support the optimization of the ion source tune. The Frankfurt Neutron Source Facility FRANZ is currently under construction. An intense beam of protons (2 MeV, 200 mA) will be used for neutron production using the Li⁷(p,n)Be⁷ reaction for studies of the astrophysical s-process. A collimation channel, which can be adjusted to allow the transport of beams with a certain beam emittance, is an ideal tool to optimize the ion source tune in terms of beam brightness. Therefore a collimation channel in the Low Energy Beam Transport section will be used. Through defined apertures and transversal phase space rotation using focusing solenoids the beam halo as well as unwanted H₂⁺ and H₃⁺ fractions will be cut. Theoretical studies which were carried out so far and a first design of the setup will be presented.

WEPS048	Dependence of Beam Loss on Vacuum Pressure Level in J-PARC Linac	beam-losses, vacuum, linac, ion	2598
	G.H. Wei KEK/JAEA, Ibaraki-Ken, Japan K. Hirano, T. Maruta, A. Miura JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan K. Ikegami J-PARC, KEK & JAEA, Ibaraki-ken, Japan
	In J-PARC linac, a 181-MeV negative hydrogen beam is supported to a succeeding 3-GeV synchrotron with normal operation power at 100-300 kW. During operation, a beam loss in the straight section of the beam transport line immediately after the linac exit is found. The residual radiation level reaches 0.3 mSv/h on the surface of the vacuum chamber several hours after the beam shutdown with the linac beam power of 12 kW. We suppose that the residual gas scattering of negative hydrogen ions generates neutral hydrogen atoms and they give rise to the beam loss by hitting the vacuum chamber wall. To confirm this speculation, the vacuum pressure level in the linac had been changed in order to find the dependence of the beam loss on it. After data analysis, we found the relationship between beam loss amplitude, which was attained from beam loss signal, and vacuum pressure was linear. Corresponding deduction and simulation has been down according to the residual gas components in linac chamber. In this paper, we present the experimental result and some simulations in this study.

WEPS098	Combined Momentum Collimation Method in High-intensity Rapid Cycling Proton Synchrotrons	synchrotron, simulation, scattering, injection	2736
	J.F. Chen, J. Tang, Y. Zou IHEP Beijing, Beijing, People's Republic of China
	A new momentum collimation method – so-called combined momentum collimation method in high-intensity synchrotrons is proposed and studied here, which makes use two-stage collimation in both the longitudinal and the transverse phase planes. The primary collimator is placed at a high-dispersion location of an arc, and the longitudinal and transverse secondary collimators are in the same arc and in the down-stream dispersion-free long straight section, respectively. The particles with positive momentum deviations will be scattered and degraded by a carbon scraper and then cleaned mainly by the transverse collimators, whereas the particles with negative momentum deviations will be scattered by a tantalum scraper and mainly cleaned by the longitudinal secondary collimators in the successive turns. Numerical simulation results using TURTLE and ORBIT codes show that this method gives high collimation efficiency for medium-energy synchrotrons. The studies have also shown two interesting effects: one is that the momentum collimation is strongly dependent on the transverse beam correlation; the other is that the material for the primary collimator plays an important role in the method. This work was supported by the National Natural Science Foundation of China (10975150, 10775153), the CAS Knowledge Innovation Program-“CSNS R&D Studies”.

THOAA03	Overview of LHC Beam Loss Measurements	beam-losses, luminosity, quadrupole, proton	2854
	B. Dehning, A.E. Dabrowski, M. Dabrowski, E. Effinger, J. Emery, E. Fadakis, V. Grishin, E.B. Holzer, S. Jackson, G. Kruk, C. Kurfuerst, A. Marsili, M. Misiowiec, E. Nebot Del Busto, A. Nordt, A. Priebe, C. Roderick, M. Sapinski, C. Zamantzas CERN, Geneva, Switzerland E. Griesmayer CIVIDEC Instrumentation, Wien, Austria
	The LHC beam loss monitoring system based on ionization chambers is used for machine protection, quench prevention and accelerator optimization. After one full year of operation it can be stated that its main functionality, that of the protection of equipment, has proven to be very robust with no issues observed for hundreds of critical beam loss events and the number of false beam aborts well below expectation. In addition the injection, dump and collimation system make regular use of the published loss measurements for system analysis and optimisation, such as the determination of collimation efficiency in order to identify possible intensity limitations as early as possible. Intentional magnet quenches have been performed to verify both the calibration accuracy of the system and the accuracy of the loss pattern predictions from simulations. Tests have also been performed with fast loss detectors based on single- and polycrystalline CVD diamond, which are capable of providing nanosecond resolution time loss structure. This presentation will cover all of these aspects and give an outlook on future performance.
	Slides THOAA03 [1.972 MB]

THOBB03	Research and Development of Novel Advanced Materials for Next-generation Collimators	impedance, radiation, target, beam-losses	2888
	A. Bertarelli, G. Arnau-Izquierdo, F. Carra, A. Dallocchio, M. Gil Costa, N. Mariani CERN, Geneva, Switzerland
	Funding: This work has partly been carried out through the European Coordination for Accelerator Research and Development (EuCARD), co-sponsored by EU 7th Framework Program. The study of innovative collimators is essential to handle the high energy particle beams required to explore unknown territory in basic research. This calls for the development of novel advanced materials, as no existing metal-based or carbon-based material possesses the combination of physical, thermal, electrical and mechanical properties, imposed by collimator extreme working conditions. A new family of materials, with promising features, has been identified: metal-diamond composites. These materials are to combine the outstanding thermal and physical properties of diamond with the electrical and mechanical properties of metals. The best candidates are Copper-Diamond (Cu-CD) and Molybdenum-Diamond (Mo-CD). In particular, Mo-CD may provide interesting properties as to mechanical strength, melting temperature, thermal shock resistance and, thanks to its balanced material density, energy absorption. The research program carried out on these materials at CERN and collaborating partners is presented, mainly focusing on the theoretical investigation, material characterization, and manufacturing processes.
	Slides THOBB03 [3.948 MB]

THPS035	Collimator Upgrade Plan of the J-PARC Main Ring	radiation, injection, beam-losses, septum	3496
	M.J. Shirakata, K. Ishii, C. Kubota, T. Oogoe, J. Takano KEK, Ibaraki, Japan Y. Kuniyasu MELCO SC, Tsukuba, Japan Y. Takiyama JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
	A halo collimation system is prepared in the middle of injection-straight section in order to localize the beam loss occurred in main ring. It consists of three collimator units. The first unit scatters halo components, and the other two units work as halo catchers. The permitted amount of beam losses in the collimator section is designed to be 450 W at the present. The upgrade plan of halo collimation system is running in order to achieve about ten times larger beam loss capability for high-power beam operation. The collimator upgrade is planned by installing a new collimator set and radiation shields which cover the collimator section. New collimator units are designed to be able to line-out the jaw with a part of radiation shield including the mechanical devices. The design work of collimator units and radiation shields is presented in this report.

THPS050	The High Energy Beam Transport System for the European Spallation Source	target, linac, quadrupole, octupole	3538
	A.I.S. Holm, S.P. Møller, H.D. Thomsen ISA, Aarhus, Denmark
	As part of the accelerator design update for the European Spallation Source (ESS), we present results from a detailed study of the High Energy Beam Transport (HEBT) line. The HEBT is a transport line around 100 m long, which connects the 2.5-GeV linac to the target. The linac will deliver a current of 50 mA, a pulse length of 2 ms and a repetition rate of 20 Hz, and losses are of utmost importance. Presumably, the HEBT will continue the 10 m period focusing structure of the linac. Two bends – overall, achromatic – will be needed to connect the different vertical levels between the linac and the target. A number of design aspects will be discussed here: space for future linac cryostats, the need and location for collimation, the location of the tuning beam dump and the associated beam optics, and the beam expander system, which provide the desired beam footprint on the target (see also separate contribution). A proposed design including options will be described together with hardware specifications.

THPZ026	Collimation Dependent Beam Lifetime and Loss Rates in the LHC	luminosity, insertion, beam-losses, betatron	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	alignment, proton, closed-orbit, beam-losses	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.

THPZ028	Upgrade Studies for the LHC Collimators	alignment, proton, betatron, quadrupole	3750
	A. Rossi, R.W. Assmann, D. Wollmann CERN, Geneva, Switzerland
	The Phase-I LHC Collimation System has to be upgraded to work at high intensity and energy. Theoretical and engineering studies are focusing on different regions of the machine. The IR3 combined momentum and betatron cleaning, initially approved for installation, has presently been kept as fallback solution in case radiation to equipment limits LHC performance. The installation of collimators in the dispersion suppressor section DS3 has been delayed. In this paper we present predictions with matched optics and the effect of machine imperfections on the collimation performance with IR3 combined cleaning, with and without DS3 collimators.

THPZ029	Principles for Generation of Time-dependent Collimator Settings during the LHC Cycle	injection, optics, controls, beam-losses	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	beam-losses, luminosity, superconducting-magnet, proton	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.

THPZ031	Acoustic Measurements in the Collimation Region of the LHC	background, radiation, beam-losses, proton	3759
	D. Deboy, R.W. Assmann, C. Baccigalupi, F. Burkart, M. Cauchi, C.S. Derrez, J. Lendaro, A. Masi, S. Redaelli, G. Spiezia, D. Wollmann CERN, Geneva, Switzerland
	The LHC accelerator at CERN has the most advanced collimation system ever being installed. The collimators intercept unavoidable particle losses and therefore are essential to avoid beam induced quenches of the superconducting magnets. In addition, they provide passive machine protection against mis-kicked beams. During material robustness tests on a LHC collimator prototype in 2004 and 2006, vibration and acoustic measurements have shown that a beam impact detection system should be feasible using accelerometers and microphones as sensors in the LHC. Recently, such sensors have been installed close to the primary collimators in the LHC tunnel. First analyses of raw data show that the system is sensitive enough to detect beam scraping on collimators. Therefore, the implementation of a sophisticated acoustic monitoring system is under investigation. It may be useful not only to detect beam impacts on primary collimators in case of failure, but also to derive further information on beam losses that occur during regular operation. This paper gives an overview on the recent installation, results of the acoustic measurements made at the LHC, and future plans.

THPZ032	Evaluation of the Combined Betatron and Momentum Cleaning in Point 3 in Terms of Cleaning Efficiency and Energy Deposition for the LHC Collimation Upgrade	betatron, quadrupole, beam-losses, proton	3762
	L. Lari, R.W. Assmann, V. Boccone, M. Brugger, F. Cerutti, A. Ferrari, A. Rossi, R. Versaci, V. Vlachoudis, D. Wollmann CERN, Geneva, Switzerland A. Faus-Golfe, L. Lari IFIC, Valencia, Spain A. Mereghetti UMAN, Manchester, United Kingdom
	Funding: This work has been carried out through of the European Coordination for Accelerator Research and Development (EuCARD), co-sponsored by EU 7th Framework Program. The Phase I LHC Collimation System Upgrade could include moving part of the Betatron Cleaning from LHC Point 7 to Point 3 to improve both operation flexibility and intensity reach. In addition, the partial relocation of beam losses from the current Betatron cleaning region at Point 7 will mitigate the risks of Single Event Upsets to equipment installed in adjacent and partly not adequate shielded areas. A combined Betatron and Momentum Cleaning scenario at Point 3 implies the installation of new collimators and a new collimator aperture layout. This paper shows the whole LHC Collimator Efficiency variation with the new layout proposed at different beam energies. As part of the evaluation, energy deposition distribution in the IR3 region gives indications about the effect of this new implementation not only on the collimators themselves but also on the other beam line elements.

THPZ033	Operational Experience and Performance of the LHC Collimator Controls System	controls, monitoring, collider, optics	3765
	S. Redaelli, A. Masi CERN, Geneva, Switzerland
	In order to handle stored energies up to 360 MJ, the LHC relies on a collimation system that consists of 100 movable collimators. Compared to other accelerator, the complexity of this system is unique: more than 400 motors and about 600 interlocked position sensors must be controlled in all the machine phases in order to ensure the cleaning and machine protection roles of the system. In this paper, the controls system and the setting management are presented and the operational experience accumulated in the 2 first years of operation is discussed, focussing in particular on failure and availability statistics during the LHC operation.

THPZ034	Semi-automatic Beam-based Alignment Algorithm for the LHC Collimation System	alignment, controls, beam-losses, feedback	3768
	G. Valentino, R.W. Assmann, S. Redaelli, N.J. Sammut, D. Wollmann CERN, Geneva, Switzerland G. Valentino University of Malta, Information and Communication Technology, Msida, Malta
	Full beam-based alignment of the LHC collimation system was a lengthy procedure as the collimators were set up manually. A yearly alignment campaign has been sufficient for now, although in future this may lead to a decrease in the cleaning efficiency if machine parameters such as the beam orbit drift over time. Automating the collimator setup procedure can allow for more frequent alignments, therefore reducing this risk. This paper describes the design and testing of a semi-automatic algorithm as a first step towards a fully automatic setup. Its implementation in the collimator control software and future plans are described.

THPZ035	Comparison of LHC Collimation Setups with Manual and Semi-automatic Collimator Alignment	alignment, beam-losses, injection, insertion	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

Other Keywords

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MOPS080

Comparison of the Current LHC Collimators and the SLAC Phase 2 Collimator Impedances

impedance, coupling, simulation, cavity

790

H.A. Day, R.M. Jones
UMAN, Manchester, United Kingdom
F. Caspers, H.A. Day, E. Métral, B. Salvant
CERN, Geneva, Switzerland

One of the key sources of transverse impedance in the LHC has been the secondary graphite collimators that sit close to the beam at all energies. This limits the stable bunch intensity due to transverse coupled-bunch instabilities and transverse mode coupling instability. To counteract this, new secondary collimators have been proposed for the phase II upgrade of the LHC collimation system. A number of designs based on different jaw materials and mechanical designs have been proposed. A comparison of the beam coupling impedance of these different designs derived from simulations are presented, with reference to the existing phase I secondary collimator design.

TUOAA02

Status of UA9, the Crystal Collimation Experiment in the SPS

ion, proton, simulation, beam-losses

897

W. Scandale
LAL, Orsay, France

Funding: CERN, IHEP-Protvino, Imperial-College, INFN, JINR-Dubna, LBNL, PNPI-Gartchina, SLAC
UA9 was operated in the CERN-SPS for more than two years in view of investigating the feasibility of the halo collimation with bent crystals. Silicon crystals 2 mm long with bending angles of about 150 urad were used as primary collimators. The crystal collimation process was steadily achieved through channeling with high efficiency. The crystal orientation was easily set and optimized with the installed goniometer which has an angular reproducibility of about ± 10 μrad. In channeling orientation, the loss rate of the halo particles interacting with the crystal is reduced by a factor of ten, whilst the residual off-momentum halo escaping from the crystal-collimator area is reduced by a factor five. The crystal channeling efficiency of about 75 % is reasonably consistent with simulations and with single pass data collected in the North Area of the SPS. The accumulated observations, shown in this paper, support our expectation that the coherent deflection of the beam halo by a bent crystal should considerably help in enhancing the collimation efficiency in LHC.

Slides TUOAA02 [4.297 MB]

TUPS013

Development of the H0 Dump Branch Duct for the Additional Collimation System in J-PARC RCS

septum, shielding, beam-losses, vacuum

1545

M. Yoshimoto
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan

For the new collimation system in the J-PARC RCS, we have the H0 branch duct installed at the dump septum magnet remodeled. This new branch duct is made of the two kinds of the stainless steels as follows; austenitic stainless steel, SUS316L and ferritic stainless steel, SUS430. In order to research on the property of the SUS430, test ducts were made in various heat-treating condition. In this presentation, we report the design of the new H0 branch duct and the study results with the test ducts.

TUPS032

Overview of EuCARD Accelerator and Material Research at GSI

ion, radiation, heavy-ion, quadrupole

1602

J. Stadlmann, H. Kollmus, E. Mustafin, N. Pyka, P.J. Spiller, I. Strašík, N.A. Tahir, M. Tomut, C. Trautmann
GSI, Darmstadt, Germany
L.H.J. Bozyk
TU Darmstadt, Darmstadt, Germany

Funding: EuCARD is co-funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 227579
EuCARD is a joined accelerator R&D initiative funded by the EU. Within this program, GSI Darmstadt is performing R&D on materials for accelerators and collimators in WP8(ColMat). GSI covers prototyping and testing of a cryogenic ion catcher for FAIR's main synchrotron SIS100, simulations and studies on activation of accelerator components e.g. halo collimatiors as well as irradiation experiments on materials foreseen to be used in FAIR accelerators and the LHC upgrade program. Carbon-carbon composites, silicon carbide and copper-diamond composite samples have been irradiated with heavy ions at various GSI beamlines and their radiation induced property changes were characterized. Numerical simulations on the possible damage by LHC and SPS beams to different targets have been performed. Simulations and modelling of activation and long term radiation induced damage to accelerator components have started. A prototype ion catcher has been built and first experiments have been performed in 2011. New collaborations with other institutes and industry in the EuCARD framework have been established and findings of the joined R&D effort influence decisions in the FAIR project and LHC upgrade.

TUPS033

Foil Scattering Loss Mitigation by the Additional Collimation System of J-PARC RCS

injection, vacuum, septum, scattering

1605

K. Yamamoto, H. Harada, J. Kamiya, Y. Yamazaki, M. Yoshimoto
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan

In the RCS, the significant losses were observed at the branch of H0 dump line and the Beam Position Monitor which was put at the downstream of the H0 dump branch duct. From the beam study, we were certain that these losses were caused by the scattering of the injection and circulating beam at the charge exchange injection foil. In order to mitigate these losses, we started to develop a new collimation system in the H0 branch duct. We presents a overview of this new collimation system.

TUPS035

LHC Collimators with Embedded Beam Position Monitors: A New Advanced Mechanical Design

alignment, pick-up, simulation, radiation

1611

A. Dallocchio, A. Bertarelli, C.B. Boccard, F. Carra, M. Gasior, L. Gentini, M.A. Timmins
CERN, Geneva, Switzerland

The LHC collimation system, ensuring both functions of beam cleaning and machine protection, is potentially submitted to high-energy beam impacts. Currently the collimators setup is performed by monitoring beam losses generated by the collimator jaws when approaching the particle beam. This procedure is applied to all LHC collimators (almost one hundred), taking several hours, and needs to be repeated if beam settings change significantly. Furthermore, during the beam-based alignment, the LHC tertiary collimators are potentially exposed to abnormal losses entailing possible damage to their tungsten jaws. To improve the efficiency of the machine operation and better control the particle beam a new advanced design embedding Beam Position Monitors (BPM) into the movable collimator jaws has been developed. This paper describes the mechanical design of various types of future collimators with embedded BPMs. Experimental measurements performed on a simplified functional prototype installed in the CERN SPS showed that, thanks to on-board BPMs, the collimator could be precisely, rapidly, and safely aligned and the beam position accurately measured.

TUPS037

Preliminary Assessment of Beam Impact Consequences on LHC Collimators

simulation, proton, controls, beam-losses

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.

TUPS041

Thermo-mechanical Study of a CLIC Bunch Train hitting a Beryllium Energy Spoiler Model

radiation, wakefield, simulation, linac

1629

J.-L. Fernández-Hernando, D. Angal-Kalinin
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
J. Resta-López
IFIC, Valencia, Spain

A thermo-mechanical study of the impact a CLIC bunch train has over a beryllium energy spoiler has been made. Beryllium has a high electrical and thermal conductivity which together with a large radiation length compared to other metals makes it an optimal candidate for a long tapered design spoiler that will not generate high wakefields, which might degrade the orbit stability and affect the collider luminosity. This paper shows the progress made from the paper presented last year in IPAC 2010. While in the aforementioned paper the study of the temperature and stress was made for the duration of the bunch train this time the study shows the evolution of the stress in the spoiler body 3 microseconds after the bunch train hit.

TUPZ007

First Ion Collimation Commissioning Results at the LHC

ion, betatron, simulation, proton

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

simulation, optics, scattering, background

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

simulation, proton, background, beam-losses

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

luminosity, emittance, optics, injection

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.

WEODA02

Collimation Studies with Hollow Electron Beams

electron, antiproton, gun, proton

1939

G. Stancari, G. Annala, T.R. Johnson, G.W. Saewert, V.D. Shiltsev, D.A. Still, A. Valishev
Fermilab, Batavia, USA

Funding: Fermi Research Alliance, LLC operates Fermilab under Contract DE-AC02-07CH11359 with the US Department of Energy. This work was partially supported by the US LHC Accelerator Research Program (LARP).
Recent experimental studies at the Tevatron collider have shown that magnetically confined hollow electron beams can act as a new kind of collimator for high-intensity beams in storage rings. In a hollow electron beam collimator, electrons enclose the circulating beam. Their electric charge kicks halo particles transversely. If their distribution is axially symmetric, the beam core is unaffected. This device is complementary to conventional two-stage collimation systems: the electron beam can be placed arbitrarily close to the circulating beam; and particle removal is smooth, so that the device is a diffusion enhancer rather than a hard aperture limitation. The concept was tested in the Tevatron collider using a hollow electron gun installed in one of the existing electron lenses. We describe some of the technical aspects of hollow-beam scraping and the results of recent measurements.

Slides WEODA02 [9.049 MB]

WEPC177

Collimation of High Intensity Ion Beams*

solenoid, ion, ion-source, simulation

2403

J. Pfister, O. Meusel
IAP, Frankfurt am Main, Germany
O.K. Kester
GSI, Darmstadt, Germany

Funding: HIC for FAIR
Intense ion beams with small phase space occupation (high brilliance) are mandatory to keep beam losses low in high current injector accelerators like those planned for FAIR. The low energy beam transport from the ion source towards the linac has to keep the emittance growth low and has to support the optimization of the ion source tune. The Frankfurt Neutron Source Facility FRANZ is currently under construction. An intense beam of protons (2 MeV, 200 mA) will be used for neutron production using the Li⁷(p,n)Be⁷ reaction for studies of the astrophysical s-process. A collimation channel, which can be adjusted to allow the transport of beams with a certain beam emittance, is an ideal tool to optimize the ion source tune in terms of beam brightness. Therefore a collimation channel in the Low Energy Beam Transport section will be used. Through defined apertures and transversal phase space rotation using focusing solenoids the beam halo as well as unwanted H₂⁺ and H₃⁺ fractions will be cut. Theoretical studies which were carried out so far and a first design of the setup will be presented.

WEPS048

Dependence of Beam Loss on Vacuum Pressure Level in J-PARC Linac

beam-losses, vacuum, linac, ion

2598

G.H. Wei
KEK/JAEA, Ibaraki-Ken, Japan
K. Hirano, T. Maruta, A. Miura
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
K. Ikegami
J-PARC, KEK & JAEA, Ibaraki-ken, Japan

In J-PARC linac, a 181-MeV negative hydrogen beam is supported to a succeeding 3-GeV synchrotron with normal operation power at 100-300 kW. During operation, a beam loss in the straight section of the beam transport line immediately after the linac exit is found. The residual radiation level reaches 0.3 mSv/h on the surface of the vacuum chamber several hours after the beam shutdown with the linac beam power of 12 kW. We suppose that the residual gas scattering of negative hydrogen ions generates neutral hydrogen atoms and they give rise to the beam loss by hitting the vacuum chamber wall. To confirm this speculation, the vacuum pressure level in the linac had been changed in order to find the dependence of the beam loss on it. After data analysis, we found the relationship between beam loss amplitude, which was attained from beam loss signal, and vacuum pressure was linear. Corresponding deduction and simulation has been down according to the residual gas components in linac chamber. In this paper, we present the experimental result and some simulations in this study.

WEPS098

Combined Momentum Collimation Method in High-intensity Rapid Cycling Proton Synchrotrons

synchrotron, simulation, scattering, injection

2736

J.F. Chen, J. Tang, Y. Zou
IHEP Beijing, Beijing, People's Republic of China

A new momentum collimation method – so-called combined momentum collimation method in high-intensity synchrotrons is proposed and studied here, which makes use two-stage collimation in both the longitudinal and the transverse phase planes. The primary collimator is placed at a high-dispersion location of an arc, and the longitudinal and transverse secondary collimators are in the same arc and in the down-stream dispersion-free long straight section, respectively. The particles with positive momentum deviations will be scattered and degraded by a carbon scraper and then cleaned mainly by the transverse collimators, whereas the particles with negative momentum deviations will be scattered by a tantalum scraper and mainly cleaned by the longitudinal secondary collimators in the successive turns. Numerical simulation results using TURTLE and ORBIT codes show that this method gives high collimation efficiency for medium-energy synchrotrons. The studies have also shown two interesting effects: one is that the momentum collimation is strongly dependent on the transverse beam correlation; the other is that the material for the primary collimator plays an important role in the method.
This work was supported by the National Natural Science Foundation of China (10975150, 10775153), the CAS Knowledge Innovation Program-“CSNS R&D Studies”.

THOAA03

Overview of LHC Beam Loss Measurements

beam-losses, luminosity, quadrupole, proton

2854

B. Dehning, A.E. Dabrowski, M. Dabrowski, E. Effinger, J. Emery, E. Fadakis, V. Grishin, E.B. Holzer, S. Jackson, G. Kruk, C. Kurfuerst, A. Marsili, M. Misiowiec, E. Nebot Del Busto, A. Nordt, A. Priebe, C. Roderick, M. Sapinski, C. Zamantzas
CERN, Geneva, Switzerland
E. Griesmayer
CIVIDEC Instrumentation, Wien, Austria

The LHC beam loss monitoring system based on ionization chambers is used for machine protection, quench prevention and accelerator optimization. After one full year of operation it can be stated that its main functionality, that of the protection of equipment, has proven to be very robust with no issues observed for hundreds of critical beam loss events and the number of false beam aborts well below expectation. In addition the injection, dump and collimation system make regular use of the published loss measurements for system analysis and optimisation, such as the determination of collimation efficiency in order to identify possible intensity limitations as early as possible. Intentional magnet quenches have been performed to verify both the calibration accuracy of the system and the accuracy of the loss pattern predictions from simulations. Tests have also been performed with fast loss detectors based on single- and polycrystalline CVD diamond, which are capable of providing nanosecond resolution time loss structure. This presentation will cover all of these aspects and give an outlook on future performance.

Slides THOAA03 [1.972 MB]

THOBB03

Research and Development of Novel Advanced Materials for Next-generation Collimators

impedance, radiation, target, beam-losses

2888

A. Bertarelli, G. Arnau-Izquierdo, F. Carra, A. Dallocchio, M. Gil Costa, N. Mariani
CERN, Geneva, Switzerland

Funding: This work has partly been carried out through the European Coordination for Accelerator Research and Development (EuCARD), co-sponsored by EU 7th Framework Program.
The study of innovative collimators is essential to handle the high energy particle beams required to explore unknown territory in basic research. This calls for the development of novel advanced materials, as no existing metal-based or carbon-based material possesses the combination of physical, thermal, electrical and mechanical properties, imposed by collimator extreme working conditions. A new family of materials, with promising features, has been identified: metal-diamond composites. These materials are to combine the outstanding thermal and physical properties of diamond with the electrical and mechanical properties of metals. The best candidates are Copper-Diamond (Cu-CD) and Molybdenum-Diamond (Mo-CD). In particular, Mo-CD may provide interesting properties as to mechanical strength, melting temperature, thermal shock resistance and, thanks to its balanced material density, energy absorption. The research program carried out on these materials at CERN and collaborating partners is presented, mainly focusing on the theoretical investigation, material characterization, and manufacturing processes.

Slides THOBB03 [3.948 MB]

THPS035

Collimator Upgrade Plan of the J-PARC Main Ring

radiation, injection, beam-losses, septum

3496

M.J. Shirakata, K. Ishii, C. Kubota, T. Oogoe, J. Takano
KEK, Ibaraki, Japan
Y. Kuniyasu
MELCO SC, Tsukuba, Japan
Y. Takiyama
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan

A halo collimation system is prepared in the middle of injection-straight section in order to localize the beam loss occurred in main ring. It consists of three collimator units. The first unit scatters halo components, and the other two units work as halo catchers. The permitted amount of beam losses in the collimator section is designed to be 450 W at the present. The upgrade plan of halo collimation system is running in order to achieve about ten times larger beam loss capability for high-power beam operation. The collimator upgrade is planned by installing a new collimator set and radiation shields which cover the collimator section. New collimator units are designed to be able to line-out the jaw with a part of radiation shield including the mechanical devices. The design work of collimator units and radiation shields is presented in this report.

THPS050

The High Energy Beam Transport System for the European Spallation Source

target, linac, quadrupole, octupole

3538

A.I.S. Holm, S.P. Møller, H.D. Thomsen
ISA, Aarhus, Denmark

As part of the accelerator design update for the European Spallation Source (ESS), we present results from a detailed study of the High Energy Beam Transport (HEBT) line. The HEBT is a transport line around 100 m long, which connects the 2.5-GeV linac to the target. The linac will deliver a current of 50 mA, a pulse length of 2 ms and a repetition rate of 20 Hz, and losses are of utmost importance. Presumably, the HEBT will continue the 10 m period focusing structure of the linac. Two bends – overall, achromatic – will be needed to connect the different vertical levels between the linac and the target. A number of design aspects will be discussed here: space for future linac cryostats, the need and location for collimation, the location of the tuning beam dump and the associated beam optics, and the beam expander system, which provide the desired beam footprint on the target (see also separate contribution). A proposed design including options will be described together with hardware specifications.

THPZ026

Collimation Dependent Beam Lifetime and Loss Rates in the LHC

luminosity, insertion, beam-losses, betatron

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

alignment, proton, closed-orbit, beam-losses

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.

THPZ028

Upgrade Studies for the LHC Collimators

alignment, proton, betatron, quadrupole

3750

A. Rossi, R.W. Assmann, D. Wollmann
CERN, Geneva, Switzerland

The Phase-I LHC Collimation System has to be upgraded to work at high intensity and energy. Theoretical and engineering studies are focusing on different regions of the machine. The IR3 combined momentum and betatron cleaning, initially approved for installation, has presently been kept as fallback solution in case radiation to equipment limits LHC performance. The installation of collimators in the dispersion suppressor section DS3 has been delayed. In this paper we present predictions with matched optics and the effect of machine imperfections on the collimation performance with IR3 combined cleaning, with and without DS3 collimators.

THPZ029

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

injection, optics, controls, beam-losses

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

beam-losses, luminosity, superconducting-magnet, proton

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.

THPZ031

Acoustic Measurements in the Collimation Region of the LHC

background, radiation, beam-losses, proton

3759

D. Deboy, R.W. Assmann, C. Baccigalupi, F. Burkart, M. Cauchi, C.S. Derrez, J. Lendaro, A. Masi, S. Redaelli, G. Spiezia, D. Wollmann
CERN, Geneva, Switzerland

The LHC accelerator at CERN has the most advanced collimation system ever being installed. The collimators intercept unavoidable particle losses and therefore are essential to avoid beam induced quenches of the superconducting magnets. In addition, they provide passive machine protection against mis-kicked beams. During material robustness tests on a LHC collimator prototype in 2004 and 2006, vibration and acoustic measurements have shown that a beam impact detection system should be feasible using accelerometers and microphones as sensors in the LHC. Recently, such sensors have been installed close to the primary collimators in the LHC tunnel. First analyses of raw data show that the system is sensitive enough to detect beam scraping on collimators. Therefore, the implementation of a sophisticated acoustic monitoring system is under investigation. It may be useful not only to detect beam impacts on primary collimators in case of failure, but also to derive further information on beam losses that occur during regular operation. This paper gives an overview on the recent installation, results of the acoustic measurements made at the LHC, and future plans.

THPZ032

Evaluation of the Combined Betatron and Momentum Cleaning in Point 3 in Terms of Cleaning Efficiency and Energy Deposition for the LHC Collimation Upgrade

betatron, quadrupole, beam-losses, proton

3762

L. Lari, R.W. Assmann, V. Boccone, M. Brugger, F. Cerutti, A. Ferrari, A. Rossi, R. Versaci, V. Vlachoudis, D. Wollmann
CERN, Geneva, Switzerland
A. Faus-Golfe, L. Lari
IFIC, Valencia, Spain
A. Mereghetti
UMAN, Manchester, United Kingdom

Funding: This work has been carried out through of the European Coordination for Accelerator Research and Development (EuCARD), co-sponsored by EU 7th Framework Program.
The Phase I LHC Collimation System Upgrade could include moving part of the Betatron Cleaning from LHC Point 7 to Point 3 to improve both operation flexibility and intensity reach. In addition, the partial relocation of beam losses from the current Betatron cleaning region at Point 7 will mitigate the risks of Single Event Upsets to equipment installed in adjacent and partly not adequate shielded areas. A combined Betatron and Momentum Cleaning scenario at Point 3 implies the installation of new collimators and a new collimator aperture layout. This paper shows the whole LHC Collimator Efficiency variation with the new layout proposed at different beam energies. As part of the evaluation, energy deposition distribution in the IR3 region gives indications about the effect of this new implementation not only on the collimators themselves but also on the other beam line elements.

THPZ033

Operational Experience and Performance of the LHC Collimator Controls System

controls, monitoring, collider, optics

3765

S. Redaelli, A. Masi
CERN, Geneva, Switzerland

In order to handle stored energies up to 360 MJ, the LHC relies on a collimation system that consists of 100 movable collimators. Compared to other accelerator, the complexity of this system is unique: more than 400 motors and about 600 interlocked position sensors must be controlled in all the machine phases in order to ensure the cleaning and machine protection roles of the system. In this paper, the controls system and the setting management are presented and the operational experience accumulated in the 2 first years of operation is discussed, focussing in particular on failure and availability statistics during the LHC operation.

THPZ034

Semi-automatic Beam-based Alignment Algorithm for the LHC Collimation System

alignment, controls, beam-losses, feedback

3768

G. Valentino, R.W. Assmann, S. Redaelli, N.J. Sammut, D. Wollmann
CERN, Geneva, Switzerland
G. Valentino
University of Malta, Information and Communication Technology, Msida, Malta

Full beam-based alignment of the LHC collimation system was a lengthy procedure as the collimators were set up manually. A yearly alignment campaign has been sufficient for now, although in future this may lead to a decrease in the cleaning efficiency if machine parameters such as the beam orbit drift over time. Automating the collimator setup procedure can allow for more frequent alignments, therefore reducing this risk. This paper describes the design and testing of a semi-automatic algorithm as a first step towards a fully automatic setup. Its implementation in the collimator control software and future plans are described.

THPZ035

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

alignment, beam-losses, injection, insertion

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.