| Paper | Title | Page |
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| WEOAG02 | Measurements of Heavy Ion Beam Losses from Collimation | 1906 |
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| The collimation efficiency for Pb82+ ion beams in the LHC is predicted to be much lower than for protons. Nuclear fragmentation and electromagnetic dissociation in the primary collimators create fragments with a wide range of Z/A ratios, which are not intercepted by the secondary collimators but lost where the dispersion has grown sufficiently large. In this article we present measurements of loss patterns caused by a prototype LHC collimator in the CERN SPS. The loss maps show a qualitative difference between Pb82+ ions and protons, with the maximum loss rate observed at different places in the ring. This behaviour was predicted by simulations and provides a valuable benchmark of the simulations done for the LHC. | ||
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| WEPP068 | Impact Distribution of the Beam Losses at the LHC Collimators in Case of Magnet Failures | 2674 |
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| During LHC operation, magnet failures may affect the beam optics leading to proton losses in the collimators. These losses, with about 360MJ of stored energy per beam at nominal collision operation, are potentially dangerous for the accelerator equipment. The LHC Machine Protection Systems ensure that the beam is extracted safely before these losses can produce any damage. As a magnet failure develops, so does the distribution of the lost particles, longitudinally along the ring as well as transversally at each collimator. The transversal impact distributions of lost particles at the most affected collimators and their evolution with time have been studied for representative magnet failures in the LHC. It has been found that the impact distribution at a given collimator can be approximated by an exponential function with time-dependent parameters. The average impact parameter ranges from about 7 to 620 μm for the cases studied. | ||
| WEPP070 | High Efficiency Collimation with Bent Crystals | 2680 |
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| A revolutionary collimation approach is being developed by the H8RD22 collaboration. The basic idea is to replace the amorphous jaws, which spread the beam halo in the whole solid angle, with bent crystals, which are able to deviate the halo particles in a given direction outside the beam core. Studies to investigate the bent crystal properties have been carried out over the past 3 years at the H8 beam line (CERN SPS) with a 400 GeV/c proton beam. The crucial result of these studies is the observation of the Volume Reflection effect, the coherent scattering of the beam on the crystalline plane which provides a small but very efficient (respectively, 14 μrad and 98% at 400 GeV/c) particle deflection. The high efficiency (which should increase at higher energy) combined with a large angular acceptance (~100 μrad) led to the development of multi-reflection systems to increase the deflection angle. Nowadays this system has reached the stage to be tested in a circular accelerator as a primary collimator to verify the effective collimation efficiency in a complex environment. The second phase of the LHC collimation could be the first application of this crystal based system. | ||
| WEPP071 | Preliminary Exploratory Study of Different Phase II Collimators | 2683 |
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| The LHC collimation system is installed and commissioned in different phases, following the natural evolution of the LHC performance. To improve cleaning efficiency towards the end of the low beta squeeze at 7TeV, and in stable physics conditions, it is foreseen to complement the 30 highly robust Phase I secondary collimators with low impedance Phase II collimators. At this stage, their design is not yet finalized. Possible options include metallic collimators, graphite jaws with a movable metallic foil, or collimators with metallic rotating jaws. As part of the evaluation of the different designs, the FLUKA Monte Carlo code is extensively used for calculating energy deposition and studying material damage and activation. This report outlines the simulation approach and defines the critical quantities involved. | ||
| WEPP072 | Evaluation of Beam Losses and Energy Deposition for A Possible Phase II Design for LHC Collimation | 2686 |
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| The LHC beams are designed to have high stability and to be stored for many hours. The nominal beam intensity lifetime is expected to be of the order of 20h. The Phase II collimation system has to be able to handle particle losses in stable physics conditions at 7 TeV in order to avoid beam aborts and to allow correction of parameters and restoration to nominal conditions. Monte Carlo simulations are needed in order to evaluate the behavior of metallic high-Z collimators during operation scenarios using a realistic distribution of losses, which is a mix of the three limiting halo cases. Moreover, the consequences in the IR7 insertion of the worst (case) abnormal beam loss are evaluated. The case refers to a spontaneous trigger of the horizontal extraction kicker at top energy, when Phase II collimators are used. These studies are an important input for engineering design of the collimation Phase II system and for the evaluation of their effect on adjacent components. The goal is to build collimators that can survive the expected conditions during LHC stable physics runs, in order to avoid quenches of the SC magnets and to protect other LHC equipments. | ||
| WEPP073 | Simulation Studies of Impact of SPS Beam with Collimator Materials | 2689 |
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Over the past years detailed simulations were carried out to study the impact of the full LHC 7 TeV beam on a target to assess the damage caused to the equipment as a result of an accident, especially to collimators and beam absorbers, and to estimate the thickness of a sacrificial absorber that would be required to stop the beam. This study has shown that the target material will be strongly heated by the beam and transformed into plasma. It has been estimated that the beam would tunnel up to 30 m in solid copper and to about 10 m in solid carbon*. Another interesting outcome of this study was that the LHC beam could be used as a tool to study High-Energy-Density (HED) states in matter. Using the same tools, we recently studied the impact of the SPS 450 GeV proton beam on tungsten and copper targets**. It has been found that the material will be seriously damaged and some tunneling of the beam into the target is expected. It should be possible to validate the predictions with a test facility to deflect the high energy high intensity SPS beam on collimator and absorber materials that will become operational in the next years.
*N. A. Tahir et al. J. Appl. Phys. 97 (2005) 083532. |