| Paper | Title | Page |
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| MOPLT005 | An Improved Collimation System for the LHC | 536 |
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| The LHC design parameters extend the maximum stored beam energy 2-3 orders of magnitude beyond present experience. The handling of the high-intensity LHC beams in a super-conducting environment requires a high-robustness collimation system with unprecedented cleaning efficiency. For gap closures down to 2mm no beam instabilities may be induced from the collimator impedance. A difficult trade-off between collimator robustness, cleaning efficiency and collimator impedance is encountered. The conflicting LHC requirements are resolved with a phased approach, relying on low Z collimators for maximum robustness and hybrid metallic collimators for maximum performance. Efficiency is further enhanced with an additional cleaning close to the insertion triplets. The machine layouts have been adapted to the new requirements. The LHC collimation hardware is presently under design and has entered into the prototyping and early testing phase. Plans for collimator tests with beam are presented. | ||
| MOPLT021 | Attenuation and Emittance Growth of 450 GeV and 7 TeV Proton Beams in Low-Z Absorber Elements | 581 |
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| The intensity of the LHC beams will be several orders of magnitude above the damage thresholds for equipment, at 7 TeV, but also already at injection energy of 450 GeV. Passive protection of the equipment against failures during beam transfer, injection and dumping of the beam with absorbers and collimators is foreseen to ensure safe operation. Since these protection devices must be robust in case of beam impact, low-Z materials such as graphite are favored. The reduction of the energy density of the primary beam by the absorber is determined by the attenuation of the beam due to nuclear collisions and the emittance growth of the surviving protons due to scattering processes. Absorbers with low density materials tend to be several meters long to ensure sufficient reduction of the transverse energy density of the impacting beam. The physics principles leading to attenuation and emittance growth for a hadron beam traversing matter are summarised, and FLUKA simulation results for 450 GeV and 7TeV proton beams on low-Z absorbers are compared with theoretical predictions. Design criteria for the LHC absorbers can be derived from these results. As an example, for the transfer line from SPS to LHC a short, low-Z absorber has been proposed to protect the LHC injection elements. | ||
| MOPLT034 | Possible Causes and Consequences of Serious Failures of the LHC Machine Protection System | 620 |
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| The LHC machine protection systems, including the beam dumping system, are designed to ensure that failures leading to serious damage to the LHC during its lifetime are extremely unlikely. These kind of failures have to date been considered as being ?beyond the design case?, for instance requiring a combination of equipment failure and surveillance failure. However, they need to be evaluated to determine the required safety levels of the protection systems. A second objective is to understand if measures can and should be taken to further reduce the probability of such failures, or to minimise their impact. This paper considers various serious failure modes of the different machine protection systems. The probable consequences and possible ameliorating measures of the worst-case scenarios are discussed. The particular case of having a stored beam with an unavailable beam dumping system is mentioned, together with possible actions to be taken in such an event. | ||
| MOPLT042 | Interaction of the CERN Large Hadron Collider (LHC) Beam with Solid Metallic Targets | 641 |
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The LHC will operate at 7 TeV with a luminosity of 1034 cm-2s-1. This requires two beams, each with 2808 bunches. The nominal intensity per bunch is 1.1 1011 protons. The energy stored in each beam of 350 MJ could heat and melt 500 kg of copper. Protection of machine equipment in the presence of such powerful beams is essential. In this paper the mechanisms causing equipment damage in case of a failure of the machine protection system are discussed. An energetic heavy ion beam induces strong radial hydrodynamic motion in the target that drastically reduces the density in the beam heated region [*], leading to a much longer range for particles in the material. For the interaction of the LHC proton beams with a target a similar effect is expected. We carried out two-dimensional hydrodynamic simulations of the heating of a solid copper block with a face area of 2cm x 2cm irradiated by the LHC beam with nominal parameters. We estimate that after an impact of about 100 bunches the beam heated region has expanded drastically. The density in the inner 0.5 mm decreases by about a factor of 10. The temperature in this region is about 10 eV and the pressure about 15 GPa. The material in the heated region is in plasma state while the rest of the target is in a liquid state. The bulk of the following beam will not be absorbed and continue to tunnel further and further into the target. The results allow estimating the length of a sacrificial absorber, if such device should be installed for an LHC upgrade. A very interesting "spinoff" from this work would be the study of high-energy-density states of matter induced by the LHC beam, because a specific energy deposition of 200 kJ/g is achieved after 2.5 micros.
* N.Tahir et al., Phys. Rev. E, 63, 2001 |
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| TUXLH01 | Machine Protection Issues and Strategies for the LHC | 88 |
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| For nominal beam parameters at 7 TeV/c, each of the two LHC proton beams has a stored energy of 350 MJ threatening to damage accelerator equipment in case of uncontrolled beam loss. Since the beam dump blocks are the only element of the LHC that can withstand the impact of the full beam, it is essential for the protection of the LHC that the beams are properly extracted onto the dump blocks in case of emergency. The time constants for failures leading to beam loss extend from 100 microseconds to few seconds. Several protection systems are designed to ensure safe operation, such as beam instrumentation, collimators and absorbers, and magnet protection. Failures must be detected at a sufficiently early stage and transmitted to the beam interlock system that triggers the beam dumping system. The strategy for the protection of the LHC will be illustrated starting from some typical failures. | ||
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| WEPLT043 | Detecting Failures in Electrical Circuits Leading to Very Fast Beam Losses in the LHC | 1927 |
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| Depending on the beam optics, failures in the magnet powering at locations with large beta functions could lead to very fast beam losses at the collimators, possibly within less than 10 turns. Beam loss monitors would normally detect such losses and trigger a beam dump. However, the available time for detection with beam loss monitors before reaching the damage level of a collimator might not be sufficient, in particular for beams with few particles in the tails. This has always been of concern and becomes even more relevant since very fast losses have been observed recently at HERA. In this paper, we present particle tracking studies for the LHC to identify failures on critical magnets. We propose a fast detection of such failures in the electrical circuit, either with highly precise hall probes for current measurement or measurements of the induced inductive voltage during the current decay. In combination with a small and simple interlock electronics such detection system can provide reliable and fast interlock signals for critical magnets in the LHC main ring but could also be used to monitor injection and extraction magnets. Depending on the properties of the electrical circuit an increase of the natural time constant of the current decay using a serial superconducting magnet is also considered. |