1. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 1 Beam Loss Monitoring System of the LHC Eva Barbara Holzer, CERN for the LHC BLM team IEEE Nuclear Science Symposium October 26, 2005 Fajardo, Puerto Rico

2. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 2 Beam Loss Monitoring System of the LHC  Specification and Requirements  Architecture of the BLM System  Threshold Calibration  Summary

3. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 3 Stored Beam Energies (Based on graph from R. Schmidt) Quench LevelsUnitsTevatronRHICHERALHC Instant loss (0.01 - 10 ms)[J/cm 3 ]4.5 10 -03 1.8 10 -02 2.1 10 -03 - 6.6 10 -03 8.7 10 -04 Steady loss (> 100 s)[W/cm 3 ]7.5 10 -02 5.3 10 -03

4. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 4 Large Hadron Collider (LHC)  In LHC there are:  514 main quadrupoles  1232 main dipoles  ~130 collimators and absorbers  pp and PbPb  Commissioning 2007

5. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 5 The BLM System: Purpose  Detection of dangerous beam losses  generation of trigger for beam extraction  Setup of the collimators and continuously monitor their performance  Localization of beam losses and identification of loss mechanism  Machine setup and studies Tevatron Collimator damage, 5.12.2003 (D. Still) LHC Collimator prototype

6. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 6 The BLM System: Challenges  Reliable (tolerable failure rate 10 -7 per hour per channel)  Reliable components, radiation tolerant electronics  Redundancy, voting  Monitoring of availability and drift of channels  Less than 2 false dumps per month (operation efficiency)  High dynamic range (10 8, 10 13 – two monitor types at the same location)  Fast (1 turn, 89  s) trigger generation for dump signal  Quench level determination with an uncertainty of a factor 2 (calibration)

7. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 7 Locations  6 detectors around each quadrupole (~3000)  Maskable: Beam abort signal can be ignored, when the stored energy in the beam is below the damage limit  Critical aperture limits or critical loss positions (~400)  Non-maskable  Collimators and absorbers (~150)  Non-maskable  Plus a set of movable BLMs  All non-maskable monitors have to be available before injection

8. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 8 Quench and Damage Levels Arc Dipole Magnet Dynamic Range Arc: 10 8 Collimator: 10 13

9. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 9 Signals from the BLM system  Dump signal to the LHC beam interlock system (LBIS), 2 types (maskable and non-maskable)  Post mortem  Up to 1000 turns plus averages of 10 minutes  Data for the control room and logging (1Hz) “Artist’s View” of the Beam Loss Display (C. Zamantzas)

10. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 10 Beam Loss Monitoring System of the LHC  Specification and Requirements  Architecture of the BLM System  Threshold Calibration  Summary

11. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 11 Monitor Types  Design criteria: Signal speed and robustness  Dynamic range (> 10 9 ) limited by leakage current through insulator ceramics (lower) and saturation due to space charge (upper limit). Ionization chamber:  N 2 gas filling at 100 mbar over- pressure  Length 50 cm  Sensitive volume 1.5 l  Ion collection time 85  s  Both monitors:  Parallel electrodes (Al, SEM: Ti) separated by 0.5 cm  Low pass filter at the HV input  Voltage 1.5 kV Secondary Emission Monitor (SEM):  Length 10 cm  P < 10 -7 bar  ~ 30000 times smaller gain

12. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 12 System Layout Threshold Comparator: Losses integrated and compared to threshold table (12 time intervals and 32 energy ranges). LBIS

13. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 13 Beam Loss Monitoring System of the LHC  Specification and Requirements  Architecture of the BLM System  Threshold Calibration  Summary

14. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 14 Threshold Determination  Beam dump threshold set to 30% of the magnet quench level  Specification:  Calibration of Thresholds:  Based on simulations  Cross-checked by measurements when possible  Beam tests might be necessary to reach the required precision  Aim of calibration  relate the BLM signal to the:  Number of locally lost beam particles  Deposited energy in the machine component  Quench and damage levels Absolute precision (calibration) factor 2 (final) factor 5 (initial) Relative precision for quench prevention < 25%

15. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 15 Warm Magnet Cold Magnet Collimator Threshold Determination  Proton loss locations (MAD-X, SIXTRACK, BeamLossPattern, measurements: LHC beam)  Hadronic showers through magnets (GEANT, measurements: HERA/DESY, LHC beam)  Magnet quench levels as function of proton energy and loss duration (SPQR, measurements: Laboratory, LHC beam)  Chamber response to the mixed radiation field in the tail of the hadronic shower (GEANT, GARFIELD, measurements: booster, SPS, H6, HERA/DESY) (S. Redaelli, L. Ponce) Injection Optics, 450 GeV, Horizontal Halo

16. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 16 Threshold Determination (E. Gschwendtner)  Proton loss locations (MAD-X, SIXTRACK, BeamLossPattern, measurements: LHC beam)  Hadronic showers through magnets (GEANT, measurements: HERA/DESY, LHC beam)  Magnet quench levels as function of proton energy and loss duration (SPQR, measurements: Laboratory, LHC beam)  Chamber response to the mixed radiation field in the tail of the hadronic shower (GEANT, GARFIELD, measurements: booster, SPS, H6, HERA/DESY)

17. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 17 Threshold Determination  Proton loss locations (MAD-X, SIXTRACK, BeamLossPattern, measurements: LHC beam)  Hadronic showers through magnets (GEANT, measurements: HERA/DESY, LHC beam)  Magnet quench levels as function of proton energy and loss duration (SPQR, measurements: Laboratory, LHC beam)  Chamber response to the mixed radiation field in the tail of the hadronic shower (GEANT, GARFIELD, measurements: booster, SPS, H6, HERA/DESY) 3 Vacuum tube First layerSecond layer Spacers Conductors Cryogenic System metal helium insulation  -channels Inner layerOuter layer Helium heat source (D. Bocian)

18. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 18 Threshold Determination  Proton loss locations (MAD-X, SIXTRACK, BeamLossPattern, measurements: LHC beam)  Hadronic showers through magnets (GEANT, measurements: HERA/DESY, LHC beam)  Magnet quench levels as function of proton energy and loss duration (SPQR, measurements: Laboratory, LHC beam)  Chamber response to the mixed radiation field in the tail of the hadronic shower (GEANT, GARFIELD, measurements: booster, SPS, H6, HERA/DESY)

19. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 19 Beam Loss Monitoring System of the LHC  Specification and Requirements  Architecture of the BLM System  Threshold Calibration  Summary

20. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 20 Summary – Features of the BLM System  Large dynamic range  High reliability and low false beam abort rate (radiation tolerant electronics, fail safe design)  Extensive simulations for threshold calibration  Dynamically changing threshold values

21. Eva Barbara Holzer IEEE NSS, Puerto Rico October 26, 2005 21 The LHC BLM Team  LHC Machine Protection Working Group (http://cern.ch/lhc-mpwg)  LHC Collimation Working Group (http://cern.ch/lhc-collimation) Bernd Dehning, Ewald Effinger, Jonathan Emery, Gianfranco Ferioli, Jose Luis Gonzalez, Edda Gschwendtner, Gianluca Guaglio, Michael Hodgson, Eva Barbara Holzer, Daniel Kramer, Roman Leitner, Laurette Ponce, Virginia Prieto, Markus Stockner, Christos Zamantzas Contributions from members of the: