Paper | Title | Page |
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MOODB103 | Results of an Experiment on Hydrodynamic Tunnelling at the SPS HiRadMat High Intensity Proton Facility | 37 |
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To predict the damage for a catastrophic failure of the protections systems for the LHC when operating with beams storing 362 MJ, simulation studies of the impact of an LHC beam on targets were performed. Firstly, the energy deposition of the first bunches in a target with FLUKA is calculated. The effect of the energy deposition on the target is then calculated with a hydrodynamic code, BIG2. The impact of only a few bunches leads to a change of target density. The calculations are done iteratively in several steps and show that such beam can tunnel up to 30-35 m into a target. Validation experiments for these calculations at LHC are not possible, therefore experiments were suggested for the CERN Super Proton Synchrotron (SPS), since simulation studies with the tools used for the LHC also predict hydrodynamic tunnelling for SPS beams. An experiment at the SPS-HiRadMat facility (High-Radiation to Materials) using the 440 GeV beam with 144 bunches was performed in July 2012. In this paper we compare the results of this experiment with our calculations of hydrodynamic tunnelling. | ||
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Slides MOODB103 [40.426 MB] | |
MOODB202 | Simulations and Measurements of Cleaning with 100 MJ Beams in the LHC | 52 |
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The CERN Large Hadron Collider is routinely storing proton beam intensities of more than 100 MJ, which puts extraordinary demands on the control of beam losses to avoid quenches of the superconducting magnets. Therefore, a detailed understanding of the LHC beam cleaning is required. We present tracking and shower simulations of the LHC's multi-stage collimation system and compare with measured beam losses, which allow us to conclude on the predictive power of the simulations. | ||
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Slides MOODB202 [6.343 MB] | |
MOPWO039 | Experience with High-intensity Beam Scraping and Tail Populations at the Large Hadon Collider | 978 |
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The population of beam tails at the LHC is source of concern because even small fractions of the total beam intensity could represent a potential danger is case of slow or fast losses, e.g. caused by orbit transients or by collimator movements. Different studies have been performed using the technique of collimator scans to probe the beam tail population, for different beam energies and beam intensities. The experience accumulated during the operation at 3.5 TeV and 4 TeV is reviewed and extrapolations to higher energies are considered. | ||
MOPWO049 | Lifetime Analysis at High Intensity Colliders Applied to the LHC | 1005 |
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The beam lifetime is one of the main parameters to define the performance of a collider. In a super-conducting machine like the LHC, the lifetime determines the intensity reach for a given collimation cleaning. The beam lifetime can be calculated from the direct measurement of beam current. However, due to the noise in the beam current signal only an average lifetime over several seconds can be calculated. We propose here an alternative method, which uses the signal of the beam loss monitors in the vicinity of the primary collimators to get the instantaneous beam lifetime at the collimators. In this paper we compare the lifetime from the two methods and investigate the minimum lifetime over the LHC cycle for all the physics fills in 2011 and 2012. These data provide a reference for estimates of performance reach from collimator cleaning. | ||
TUPFI012 | HL-LHC: Integrated Luminosity and Availability | 1352 |
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The objective of LHC operation is to optimise the output for particle physics by maximising the integrated luminosity. An important constraint comes from the event pile–up for one bunch crossing that should not exceed 140 events per bunch crossing. With bunches every 25 ns the luminosity for data taking of the experiments should therefore not exceed 5*1034 s−1cm-2. For the optimisation of the integrated luminosity it is planned to design HL-LHC for much higher luminosity than acceptable for the experiments and to limit the initial luminosity by operating with larger beam size at the collision points. During the fill, the beam size will be slowly reduced to keep the luminosity constant. The gain from luminosity levelling depends on the average length of the fills. Today, with the LHC operating at 4 TeV, most fills are terminated due to equipment failures, resulting in an average fill length of about 5 h. In this paper we discuss the expected integrated luminosity for HL-LHC as a function of fill length and time between fills, depending on the expected MTBF of the LHC systems with HL-LHC parameters. We derive an availability target for HL-LHC and discuss steps to achieve this. | ||
TUPME032 | Update on Beam Induced RF Heating in the LHC | 1646 |
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Since June 2011, the rapid increase of the luminosity performance of the LHC has come at the expense of increased temperature and pressure readings on specific near-beam LHC equipment. In some cases, this beam induced heating has caused delays whilie equipment cools down, beam dumps and even degradation of these devices. This contribution gathers the observations of beam induced heating attributable to beam coupling impedance, their current level of understanding and possible actions that are planned to be implemented during the long shutdown in 2013-2014. | ||
THPEA045 | Beam Induced Quenches of LHC Magnets | 3243 |
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In the years 2009-2013 LHC was operating with the beam energy of 3.5 and 4 TeV instead of the nominal 7 TeV, with the corresponding currents in the superconducting magnets also half nominal. To date only a small number of beam-induced quenches have occurred, with most being due to specially designed quench tests. During normal collider operation with stored beam there has not been a single beam induced quench. This excellent result is mainly explained by the fact that the cleaning of the beam halo worked very well and, in case of beam losses, the beam was dumped before any significant energy was deposited in the magnets. However, conditions are expected to become much tougher after the long LHC shutdown, when the magnets will be working at near nominal currents in the presence of high energy and intensity beams. This paper summarizes the experience to date with beam-induced quenches. It describes the techniques used to generate controlled quench conditions which were used to study the limitations. Results are discussed along with their implication for LHC operation after the first Long Shutdown. | ||
THPEA046 | Machine Protection at the LHC - Experience of Three Years Running and Outlook for Operation at Nominal Energy | 3246 |
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With above 22fb-1 integrated luminosity delivered to the experiments ATLAS and CMS the LHC surpassed the results of 2011 by more than a factor 5. This was achieved at 4TeV, with intensities of ~2e14p per beam. The uncontrolled loss of only a small fraction of the stored beam is sufficient to damage parts of the sc. magnet system, accelerator equipment or the particle physics experiments. To protect against this a correct functioning of the complex LHC machine protection (MP) systems through the operational cycle is essential. Operating with up to 140MJ stored beam energy was only possible due to the experience and confidence gained in the two previous running periods, where the intensity was slowly increased. In this paper the 2012 performance of the MP systems is discussed. The strategy applied for a fast, but safe, intensity ramp up and the monitoring of the MP systems during stable running periods are presented. Weaknesses in the reliability of the MP systems, set-up procedures and setting adjustments for machine development periods, discovered in 2012, are critically reviewed and improvements for the LHC operation after the up-coming long shut-down of the LHC are proposed. | ||
THPEA047 | Diamond Particle Detector Properties during High Fluence Material Damage Tests and their Future Applications for Machine Protection in the LHC | 3249 |
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Experience with LHC machine protection (MP) during the last three years of operation shows that the MP systems sufficiently protect the LHC against damage in case of failures leading to beam losses with a time constant exceeding 1ms. An unexpected fast beam loss mechanism, called UFOs, was observed, which could potentially quench superconducting magnets. For such fast losses, but also for better understanding of slower losses, an improved understanding of the loss distribution within a bunch train is required. Diamond particle detectors with bunch-by-bunch resolution and high dynamic range have been developed and successfully tested in the LHC and in experiments to quantify the damage limits of LHC components. This paper will focus on experience gained in use of diamond detectors. The properties of these detectors were measured during high-fluence material damage tests in CERN's HiRadMat facility. The results will be discussed and compared to the cross-calibration with FLUKA simulations. Future applications of these detectors in the LHC to understand beam losses and to improve the protection against fast particle losses will be discussed. | ||
THPFI059 | Robustness Test of a Silicon Strip Crystal for Crystal-assisted Collimation Studies in the LHC | 3427 |
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Over the past years, the UA9 experiment has successfully demonstrated the viability of enhancing the collimation efficiency of proton and ion beams in the SPS by means of bent crystals. An extension of UA9 to the LHC has been recently approved. The conditions imposed by the LHC operational environment, in particular the tremendous energy density of the beam, require a reliable understanding of the crystal integrity in view of potential accident scenarios such as an asynchronous beam dump. For this purpose, irradiation tests have been performed at the CERN-HiRadMat facility to examine the mechanical strength of a silicon strip crystal in case of direct beam impact. The tests were carried out using a 440 GeV proton beam of 0.5 mm transverse size. The crystal, 3 mm long in beam direction, was exposed to a total of 2*1014 protons, with individual pulse intensities reaching up to 3*1013. First visual inspections reveal no macroscopic damage to the crystal. Complementary post-irradiation tests are foreseen to assess microscopic lattice damage as well as the degradation of the channelling efficiency.
On behalf of the UA9 Collaboration. |
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