Verification of the Beam Loss studies at start-up L. Ponce Thanks to B. Dehning, M. Sapinski, S. Redaelli, R. Assmann, B. Holzer, BLM team, Collimation team, MPSCWG,... 1

Outlines Asked questions: Presentation of the simulations Initial settings of the thresholds Commissioning with beam Changing thresholds Asked questions: Procedure for calibrating the loss patterns Operational scenarios given measured BLM losses Thresholds adjustment and masking disabling during operation 2

Preliminary remarks Procedure for HW commissioning of the BLM system has been already presented by J-J. Gras The detailed of the implementation of the system presented at the LTC Procedure for collimator settings using BLM described by R. Assmann Details of the sector test provoked quench also already presented by R. Assmann MP functionalities of the BLM system is commissioned in phase A.5 (R. Jones and J. Uythoven talks)‏ this talk is more oriented to quench prevention functionality 3

1. Details of the simulations simulation needed for positioning of the BLM and for the thresholds generation global loss pattern and local loss pattern 4

Proton/ion loss maps Protons (collimation team) : scenarios: nominal settings, worst cases, error scenarios, injection and top energies, both beams Ions (H. Braun, J. Jowet, G. Bellodi) : both beams Protons in collimation areas FLUKA simulations for IR7, triplets area, MARS for IR3 Protons: magnets failure scenarios (A. Alonso) The complementary/redundant simulations allow a detailed view of particle loss locations

Two examples from G. Robert-Demolaize's talk in Chamonix 2006 ▬► halo 6

Global loss patterns systematic analysis of all the loss maps provided in order to identify the loss locations and place BLMs BLMs at each quad, plus some extra locations: on MBs in dispersion suppressor in IR3 and 7 SEM+ IC pairs at each coll to cover the dynamic range MBs in DS and arcs for ions on standalone dipoles in LSS effect of the collimators settings is a global effect: peaks are moving from one quad to another, from an IR to another... The dominant effect is the loss in the following dispersion suppressor + ARC

“local” loss pattern same typical pattern for losses at the element level: Peak before MQ at the aperture limit End of loss at the centre of the MQ (beam size effect)‏ 8

typical results of the simulations Maximum of the shower ~ 1m after impacting point in material whatever the impacting angle and transverse position of the post protons increase of the signal in magnet free locations factor 2 between MQ and MB 20 % more in the peak amplitude by doubling the angle (typic. 0.25 mrad)‏ 40 % less in peak amplitude between the uppermost/innermost impacting point z (cm)‏ 9

Realistic “local” loss pattern The 3 monitors at the quadrupoles will show a decreasing signal in beam direction beam 2 Cross-talk signal 10

=> a total of 4000 monitors (3600 IC + 400 SEM)‏ Positions of the BLM 3 BLM per beam at each quadrupoles BLM in LSS : dipoles, collimators, warm magnets, MSI, MSD, MKD,MKB, all the masks… => a total of 4000 monitors (3600 IC + 400 SEM)‏ positions as much as possible “standardized” to limit the number of different thresholds BLM grouped in families family = same quench level and same material between the loss and the BLM)‏ 250 families Beam dump threshold set relative to quench level for cold elements or to the element damage level (need equipments experts to set the correct values) for warm element‏ 11

2. thresholds generation 12

Strategy to generate thresholds Parameterisation LHC Proj Note 44 QL instant loss calculation + simulations QL steady state loss simulations + measurements Quench level QL N protons quench = QL/Ep energy deposition in coil Ep response function Q(F)‏ particle fluence F simulations Threshold = Q(F)*Nprotons quench simulation code: FLUKA or Geant4, quench level: D. Bocian code

Ingredients of the recipe Threshold values contain : the BLM response (electronics, chamber response calibration) the position of the BLM relative to the cold masses,i.e amount of material to cross (BLM grouped by families) the ratio between the lost protons and the BLM signal (particle shower simulation) the ratio between the BLM signal and the deposited energy in the coil for the family (particle shower simulation) the knowledge of quench level and/or the damage level (W/cm3)‏ (seeds for parametrization ) the dependence of the quench/damage level on beam energy and integration time. (for parametrization of the thresholds)‏ topology of the losses 14

Calibration of the detector response calibration of all the chambers (HW commissioning)‏: all chambers are calibrated before installation + radiation source tests in situ detector model checked with the CERN/H6 experiment (M. Stockner PhD thesis) plus proton, gamma and neutron measurements measurements of the tails of the secondary shower with BLM on HERA dump : comparison with G4 simulation (M. Stockner) radiation tests for SEE studies => well controlled, expected uncertainty < 50 % 15

Relative loss levels for fast / slow losses Calibration of the quenches/damage level quench tests campaign in SM18 for quench magnet model verification (steady state losses) (D. Bocian,A. Siemko) damage level estimation : working group to re-visit the calculations 0.3 0.4 0.3 0.3 Dump threshold 1 Quench level 1000 25 320 5 Damage level 7 TeV 450 GeV Relative loss levels for fast / slow losses Arc Dipole Magnet Detection of shower particles outside the cryostat or near the collimators to determine the coil temperature increase due to particle losses LHC quench values are lowest

3.Commissioning with beam 17

Calibration of the particle shower development with beam Motivation of the test: Verification of the correlation between quench level and BLM thresholds Verify „real-life“ quench levels Verify simulated BLM signal and loss patterns Provoked magnet quench: check steady state losses quench limit with circulating beam (part of the MPS commissioning)‏ check fast losses quench behaviour with sector test => Accurately known quench levels will increase operational efficiency! 18

tests with beam: sector test see presentations of A. Koschik in CHAMONIX 06 and R. Assman at this workshop simple idea: steer pilot beam into aperture and check the BLM response to a known lost intensity slowly increase the intensity up to magnet quench to check the quench level evaluation List of priorities of the magnets to be revisited in collaboration with MPP: low quench level magnets (MQM,MQT), main magnets (MB, MQ),...

tests with beam: circulating beam check steady state losses quench limit with circulating beam (part of the MPS commissioning)‏ first proposal : R. Assman's presentation on quenches with beam second proposal : local orbit bump to slowly steer the beam to aperture at a chosen magnet. possibility to repeat the test with higher beam energy

Topology of the losses Position of the detectors optimized to catch losses from the aperture limitation and middle of the quad but a change of 25 cm in the impact point position makes a factor 2 in the signal thresholds at the worst case (conservative) or at the most likely(statistics needed)? 21

Trade-Off: Number of Quenches vs. False Aborts (-) not all quenches caught (+) no false aborts (-) all quenches caught (+) many false aborts Assumed quench limit BLM threshold given by the same simulation toolkit quench test calibration

Changing thresholds The APPLIED threshold table is set to: 30 % of the quench levels for cold elements in the most likely loss topology relative to the damage level for warm elements: proposal from R. Schmidt for safe beam flag value (conservative)‏ BLM monitor thresholds are trim able individually or by families with a recorded trim history, only possible before filling the machine For machine protection issues, trim is limited bellow a pre-defined max safe allowed value” of the different equipment (energy and integration dependant), the so-called “MASTER” table The MASTER table values are set above the quench level (factor 5?) and below the estimated damage levels values details of the implementation presented at the 86th LTC‏ in January 23

Baseline scenario The MASTER table should only be changed infrequently because this is the reference backed-up table for the BLM system APPLIED table is set to initial recommended value using pre-defined families If REALLY needed, APPLIED thresholds can be trimmed up to the MASTER table value‏ All BLM are initially configured as unmaskable, configuring a BLM as maskable should only be done under exceptional circumstances Any changes can only be done without beam in the machine (removal of the Beam_Permit)‏ Initially, only a group of few experts is allowed to do any change in the MASTER table and to TRIM the APPLIED table. (Two different groups and names can be added)‏ Detection of shower particles outside the cryostat or near the collimators to determine the coil temperature increase due to particle losses LHC quench values are lowest 24

tests with beam: warm elements simulations available for some elements, mainly collimators, but missing info for others: TDI, kickers, warm magnets ... assumptions/extrapolation are needed to set the thresholds calibration tests required: I do not propose to check the damage level! Calibration of the BLM response to a given number of protons on TDI (see V. Kain's talk)‏ same on TCT (critical element for protection)‏ Detection of shower particles outside the cryostat or near the collimators to determine the coil temperature increase due to particle losses LHC quench values are lowest 25

possible origins of the losses distinction between the global (= LHC-wise) loss pattern and the local (= quad-wise) one some examples: misalignement => local peak aperture limitation => local peak orbit bump => local peak collimators settings => global loss map injection losses => next Arc Beam blow up => global gas bump => local peak D3 failure => local peak ... intensive simulation work done but still needed to complete the catalogue

Expected results of the tests Strategy of threshold settings mainly lead by simulations All these tests allow to confirm the MODELS used for determining the thresholds optimised thresholds settings from an experimental point adjustment of the threshold levels on warm elements to the requested protection level (for example : max number of lost protons/s)‏ Then we can move to the global understanding of the loss patterns 27

scenarios given measured beam losses compare the observed loss patterns with the “catalogue” of typical signatures keep on furnishing this catalogue, before beam and with beam. courtesy of F. Follin 28

Conclusions Tests with beam are requested to validate the simulations and further reduce the number of future quenches during operation The commissioning of the BLMs with beam is well disentangled from collimator settings The bigger the catalogue of typical loss maps, the faster the understanding of the global loss maps Flexibility of thresholds adjustment exists to further optimise following operational experience (worst case or most likely)‏