Redaelli, S.

Paper	Title	Page
MOPCH091	An Alternative Nonlinear Collimation System for the LHC	246
	J. Resta-López, R.W. Assmann, S. Redaelli, J. Resta-López, G. Robert-Demolaize, D. Schulte, F. Zimmermann CERN, Geneva A. Faus-Golfe IFIC, Valencia
	The optics design of an alternative nonlinear collimation system for the LHC is presented. We discuss an optics scheme based on a single spoiler located in between a pair of skew sextupoles for betatron collimation. The nonlinear system allows opening up the collimator gaps and, thereby reduces the collimator impedance, which presently limits the LHC beam intensity. After placing secondary absorbers at optimum locations behind the spoiler, we analyze the beam losses and calculate the cleaning efficiency from tracking studies. The results are compared with those of the conventional linear collimation system.
MOPLS003	Tertiary Halo and Tertiary Background in the Low Luminosity Experimental Insertion IR8 of the LHC	532
	V. Talanov IHEP Protvino, Protvino, Moscow Region R.W. Assmann, D. Macina, K.M. Potter, S. Redaelli, G. Robert-Demolaize, E. Tsesmelis CERN, Geneva
	In our report we present the results for numerical simulation of tertiary halo and tertiary background in the LHC. We study the case of the proton losses in the betatron cleaning insertion IR7 with the subsequent tertiary halo generation in the downstream experimental insertion IR8. We analyze the formation of tertiary background in the experimental area of the IR8 and evaluate the performance of the machine-detector interface shielding with respect to this source of the background. The results obtained are compared with the previous estimates of the machine-induced background in the low luminosity insertions of the LHC, and the balance between different sources of the background is discussed.
MOPLS008	Beam Halo on the LHC TCDQ Diluter System and Thermal Load on the Downstream Superconducting Magnets	547
	B. Goddard, R.W. Assmann, A. Presland, S. Redaelli, G. Robert-Demolaize, L. Sarchiapone, Th. Weiler, W.J.M. Weterings CERN, Geneva
	The moveable single-jawed graphite TCDQ diluter must be positioned very close to the circulating LHC beam in order to prevent damage to downstream components in the event of an unsynchronised beam abort. A two-jawed graphite TCS collimator forms part of the TCDQ system. The requirement to place the TCDQ and TCS jaws close to the beam means that the system can intercept a substantial beam halo load. Initial investigations indicated a worryingly high heat load on the Q4 coils. This paper presents the updated load cases, shielding and simulation geometry, and the results of simulations of the energy deposition in the TCDQ system and in the downstream superconducting Q4 magnet. The implications for the operation of the LHC are discussed.
TUPLS017	Optics Study for a Possible Crystal-based Collimation System for the LHC	1526
	R.W. Assmann, S. Redaelli, W. Scandale CERN, Geneva
	The use of bent crystals as primary collimators has been long proposed as an option to improve the cleaning efficiency of the LHC betatron and momentum collimation systems. These systems are presently based on two-stage collimation with amorphous scatterers and absorbers. Crystals are expected to help by channeling and extracting the halo particles with large angles, resulting in higher cleaning efficiency. Independent of ongoing studies for crystal qualifications (not reported here), it is important to understand the required deflection angles and the possible locations of absorbers for the LHC layout. Optics studies have been performed in order to specify the required angles for various LHC beam energies and possible locations of absorbers for the deflected halo beam. A possible layout for crystal-assisted collimation at the LHC is discussed, aiming for a solution which would not change the LHC layout but would make use of the existing collimator location.
TUPLS018	Collimation Efficiency during Commissioning	1529
	C.B. Bracco, R.W. Assmann, A. Ferrari, S. Redaelli, G. Robert-Demolaize, M. Santana-Leitner, V. Vlachoudis, Th. Weiler CERN, Geneva
	The design of the LHC collimation system naturally focused on understanding and maximizing the ultimate performance with all collimators in place. However, for the commissioning of the LHC it is important to analyze the collimation efficiency with certain subsets of collimators, with increased collimation gaps and relaxed set-up tolerances. Special studies on halo tracking and energy deposition have been performed in order to address this question. The expected cleaning performance and intensity limits are discussed for various collimation scenarios as they might be used during commissioning and initial operation of the LHC.
TUPLS019	Critical Halo Loss Locations in the LHC	1532
	G. Robert-Demolaize, R.W. Assmann, C.B. Bracco, S. Redaelli, Th. Weiler CERN, Geneva
	The requirements on cleaning efficiency in the LHC are two to three orders of magnitude beyond the needs at existing super-conducting colliders. The LHC will therefore operate in unknown territory, which can only be assessed by powerful simulation tools. Such tools have been developed at CERN over the last years, making it possible to perform detailed simulations of the LHC cleaning processes and multi-turn loss patterns around the LHC ring. The simulation includes all collimators, diluters and absorbers in the LHC. Proton loss maps are generated with a 10 cm resolution, which allows performing advanced studies for quenches of super-conducting magnets along with the analysis of the deposited energy in the machine elements. The critical locations of beam halo losses are discussed, both for the ideal machine and for various scenarios of closed-orbit distortion and beta-beating. From these results it can be shown that it is sufficient to use a limited number of BLM's for the setup and optimization of the LHC collimation system.
TUPLS130	Comparison between Measured and Simulated Beam Loss Patterns in the CERN SPS	1810
	S. Redaelli, G. Arduini, R.W. Assmann, G. Robert-Demolaize CERN, Geneva
	A prototype of an LHC collimator has been tested with proton beams at the CERN SPS. The interaction of the circulating proton beam with the carbon collimator jaws generated showers that were lost in the downstream SPS aperture. The measured beam loss patterns are compared in detail with the results of dedicated loss simulations. The simulation package includes (1) a 6D particle tracking through the SPS lattice; (2) the scattering interaction of protons with the collimator jaw material; (3) the time-dependent displacement of the collimator jaws with respect to the beam orbit; (4) a detailed aperture model of the full SPS ring. It is shown that the simulation tools can reliably predict the measured location of losses. This provides an important assessment of the simulation tools in view of the LHC beam loss studies.
THPCH061	Tune Shift Induced by Nonlinear Resistive Wall Wake Field of Flat Collimator	2925
	F. Zimmermann, G. Arduini, R.W. Assmann, H. Burkhardt, F. Caspers, M. Gasior, O.R. Jones, T. Kroyer, E. Métral, S. Redaelli, G. Robert-Demolaize, F. Roncarolo, G. Rumolo, R.J. Steinhagen, J. Wenninger CERN, Geneva
	We present formulae for the coherent and incoherent tune shifts due to the nonlinear resistive wall wake field for a single beam traveling between two parallel plates. In particular, we demonstrate that the nonlinear terms of the resistive wall wake field become important if the gap between the plates is comparable to the transverse rms beam size. We also compare the theoretically predicted tune shift as a function of gap size with measurements for an LHC prototype graphite collimator in the CERN SPS and with simulations.
TUODFI01	The Final Collimation System for the LHC	986
	R.W. Assmann, O. Aberle, G. Bellodi, A. Bertarelli, C.B. Bracco, H.-H. Braun, M. Brugger, S. Calatroni, R. Chamizo, A. Dallocchio, B. Dehning, A. Ferrari, P. Gander, A. Grudiev, E.B. Holzer, J.-B. Jeanneret, J.M. Jimenez, M. Jonker, Y. Kadi, K. Kershaw, J. Lendaro, J. Lettry, R. Losito, M. Magistris, A.M. Masi, M. Mayer, E. Métral, R. Perret, C. Rathjen, S. Redaelli, G. Robert-Demolaize, S. Roesler, F. Ruggiero, M. Santana-Leitner, P. Sievers, M. Sobczak, E. Tsoulou, V. Vlachoudis, Th. Weiler CERN, Geneva I. Baishev, I.L. Kurochkin IHEP Protvino, Protvino, Moscow Region
	The LHC collimation system has been re-designed over the last three years in order to address the unprecedented challenges that are faced with the 360 MJ beams at 7 TeV. The layout of the LHC has now been fixed and a final approach for collimation and cleaning has been adopted. In total 132 collimator locations have been reserved in the two LHC rings and can be installed in a phased approach. Ninety collimators of five different types will be available for initial beam operation. The system has been fully optimized for avoiding quenches of super-conducting magnets during beam losses and for sufficient survival of beamline components against radioactive dose. The phased approach for LHC collimation is described, the various collimators and their functionalities are explained, and the expected system performance is summarized.
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