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Beam loss monitor system for machine protection

Beam loss monitor system for machine protection. B. Dehning CERN AB/BDI. Protection. Availability. Safety. Risk. Methods: Stop of next injection Extraction of beam. Reduction of operational efficiency. Damage (system integrity). Failsafe Redundancy Survey Check. Quench (operational

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Beam loss monitor system for machine protection

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  1. Beam loss monitor system for machine protection B. Dehning CERN AB/BDI DIPAC 2005, B.Dehning

  2. Protection Availability Safety Risk Methods: Stop of next injection Extraction of beam Reduction of operational efficiency Damage(system integrity) FailsafeRedundancy SurveyCheck Quench(operational Efficiency) Design issues: Reliable components Redundancy, voting Monitoring of drifts Systems: Beam loss Monitors Quench protection system Interlocksystem ¨ Dump system Scaling: frequency of eventsxconsequence Meantime between failures 1 10-8 to 1 10-7 1/h SIL ALARP Beam loss measurement design approach DIPAC 2005, B.Dehning

  3. Damage example and LHC consequences Tevatron, December 5, 2003 • Fast beam loss • A Roman Pot moved into beam due to a controls error • damaging of 2 collimators and 2 spool pieces LHC extrapolation • Energy in beam 7 times Tevatron • Intensity of beam 30 times Tevatron • Number of LHC of moving elements in the LHC about 200 How many Magnets and … are damaged? DIPAC 2005, B.Dehning

  4. Stored beam energies Damage and Quench threshold to first order identical => LHC will be exceptional DIPAC 2005, B.Dehning

  5. (values proportional) DESY 2.6 – 6.6 E-03 LHC Bending Magnet Quench Levels LHC quench values are lowest DIPAC 2005, B.Dehning

  6. Quench Levels and Energy Dependence • Fast decrease of quench levels between 0.45 to 2 TeV • Similar behaviour expected for damage levels DIPAC 2005, B.Dehning

  7. Failure rate and checks Systems parallel + survey + check: • in case of system failure dump beam (failsafe) • verification of functionality: simulate measurement and comparison with expected result DIPAC 2005, B.Dehning

  8. HERA Tevatron, LHC Dump requests Dump system Interlock system Role of the BLM System for the protection SOURCES of beam losses • User/operator • PC failures • Magnet failures • Collimators failures • RF failures • Obstacles • Vacuum • … DIPAC 2005, B.Dehning

  9. Beam loss measurement system layouts FNAL Examples from: LHC SNS, LHC LHC FNAL LHC DIPAC 2005, B.Dehning

  10. Ionisation chamber SNS • Stainless steal • Coaxial design, 3 cylinder (outside for shielding) • Low pass filter at the HV input • Ar, N2 gas filling at 100 mbar over pressure • Outer inner electrode diameter 1.9 / 1.3 cm • Length 40 cm • Sensitive volume 0.1 l • Voltage 2k V • Ion collection time 72 us DIPAC 2005, B.Dehning

  11. Ionisation chamber LHC • Stainless steal cylinder • Parallel electrodes separated by 0.5 cm • Al electrodes • Low pass filter at the HV input • N2 gas filling at 100 mbar over pressure • Diameter 8.9 cm • Length 60 cm • Sensitive volume 1.5 l • Voltage 1.5 kV • Ion collection time 85 us DIPAC 2005, B.Dehning

  12. Ionisation chamber measurements Signal vs voltage (SNS) Energy deposition (LHC) Beam scanned DIPAC 2005, B.Dehning

  13. Ionisation chamber currents (1 litre, LHC) DIPAC 2005, B.Dehning

  14. Gain Variation of SPS Chambers • 30 years of operation • Measurements done with installed electronic • Relative accuracy • Ds/s < 0.01 (for ring BLMs) • Ds/s < 0.05 (for Extr., inj. BLMs) • Gain variation only observed in high radiation areas • Consequences for LHC: • Nogain variation expected in the straight section and ARC of LHC • Variation of gain in collimation possible for ionisation chambers Test with Cs137 Total received dose: ring 0.1 to 1 kGy/year extr 0.1 to 10 MGy/year DIPAC 2005, B.Dehning

  15. LHC acquisition board • Current to Frequency Converters (CFCs) • Analogue to Digital Converters (ADCs) • Tunnel FPGAs: Actel’s 54SX/A radiation tolerant. • Communication links:Gigabit Optical Links. • Surface FPGAs: Altera’s Stratix EP1S40 with 780 pin. DIPAC 2005, B.Dehning

  16. 100 ns 100 ns to 100 s V out Threshold Comparator I + I - Reset time Integration time LHC tunnel card • Not very complicated design “simple” • Large Dynamic Range (8 orders) • Current-to-Frequency Converter (CFC) • Analogue-to-Digital Converter • Radiation tolerant (500 Gy, 1 107 p/s/cm2) • Bipolar • Customs ASICs • Triple module redundancy DIPAC 2005, B.Dehning

  17. FNAL beam loss integrator and digitizer • Independent operation form crate CPU (FNAL, LHC) • Thresholds managed by control card over control bus (LHC combined) VME Control bus Control bus DIPAC 2005, B.Dehning

  18. FNAL abort concentrator • Measurements and threshold are compared every 21 s (fastest) (LHC 80 s) • Channels can be masked (LHC yes) • Aborts of particular type are counted and compared to the required multiplicity value for this type (LHC: single channel will trigger abort, channel can be masked depending on beam condition) • Ring wide concentration possible (LHC no) DIPAC 2005, B.Dehning

  19. Protection Availability Safety Risk Methods: Stop of next injection Extraction of beam Reduction of operational efficiency Damage(system integrity) FailsafeRedundancy SurveyCheck Quench(operational Efficiency) Design issues: Reliable components Redundancy, voting Monitoring of drifts Systems: Beam loss Monitors Quench protection system Interlocksystem ¨ Dump system Scaling: frequency of eventsxconsequence Meantime between failures 1 10-8 to 1 10-7 1/h SIL ALARP Beam loss measurement design approach DIPAC 2005, B.Dehning

  20. Test Procedure of Analog Signal Chain • Basic concept: Automatic test measurements in between two fills • Measurement of dark current • Modulation of high voltage supply of chambers • Check of components in Ionisation chamber (R, C) • Check of capacity of chamber (insulation) • Check of cabling • Check of stable signal between few pA to some nA (quench level region) • Not checked: gas gain of chamber (only once a year with source) DIPAC 2005, B.Dehning

  21. Secondary B Signal Primary A Signal (256 bits) (256 bits) Reception ______________ _ _ Tx Check & Signal Choice ______________ _ _ Tunnel Status Check ______________ _ _ Format Data ______________ _ _ Only CRC Only CRC Check CRC Compare Check CRC validity CRCs validity (4 byte) (4 byte) Error Error Error S/W & TTL output Signal Select Error (A or B) Status Error 10-bits Truncate extra/redundant bits (leave 160 bits) DeMux 1 2 3 … 8 LHC transmission check At the Surface FPGA: • Signal CRC-32 • Error check / detection algorithm for each of the signals received. • Comparison of the pair of signals. • Select block • Logic that chooses signal to be used • Identifies problematic areas. • Tunnel’s Status Check block • HT, Power supplies • FPGA errors • Temperature DIPAC 2005, B.Dehning

  22. Reliability Study (LHC) by G. Guaglio Relative probability of a system component being responsible for a damage to an LHC magnet in the case of a loss. Relative probability of a BLM component generating a false dump. Highest damage probability given by the Ionisation chamber (80%) because: Reduced checks Harsh environment Most false dumps initiated by analog front end (98%) because: Reduced check Quantity Harsh environment DIPAC 2005, B.Dehning

  23. Beam Loss Display DIPAC 2005, B.Dehning

  24. Literature • SNS, Ion chamber, R.C. Witkover, BIW02 • FNAL, BLM electronics, J.D. Lewis et al., IEEE 04 • http://ab-div-bdi-bl-blm.web.cern.ch/ab-div-bdi-bl-blm • LHC • Reliability issues, G. Guaglio et al., BIW04, R. Filippini et al., PAC 05 • Front end electronics, analog, thesis, W. Friesenbichler • Digital signal transmission, thesis, R. Leitner • Digital signal treatment, C. Zamantzas, this workshop DIPAC 2005, B.Dehning

  25. Reserve slides DIPAC 2005, B.Dehning

  26. Approximation of Quench Levels (LHC) • Dump level tables are loaded in a non volatile RAM • Any curve approximation possible • Loss durations • Energy dependence Relative error kept < 20 % DIPAC 2005, B.Dehning

  27. Drift times of electrons and ions (II) DIPAC 2005, B.Dehning

  28. Drift times of electrons and ions (I) DIPAC 2005, B.Dehning

  29. neutron proton pi+ pi- Gamma e+ e- u+ u- Response of ion chambers for different particle species Due to attenuation ofshower => increase of non linearity of chamber response DIPAC 2005, B.Dehning

  30. Quench level and observation range 450 GeV 7 TeV BLMS* & BLMC Damage levels Dynamic Arc: 108 Collimator: 1013 Special & Collimator1 turn Arc 2.5 ms Quench and Damage Levels • Detection of shower particles outside the cryostat or near the collimators to determine the coil temperature increase due to particle losses DIPAC 2005, B.Dehning

  31. 1 bin = 5 MeV Energy [GeV] Energy spectrum of shower particles outside of cryostat • Number of charged particles and energy deposition simulated: • Energy spectrum: DIPAC 2005, B.Dehning

  32. Ionisation Chamber Time Response Measurements (BOOSTER) Chamber beam response Chamber current vs beam current slength proton= 50 ns 80 % of signalin one turn Intensity discrepancy by a factor two FWHMe-= 150 ns Intensity density: - Booster 6 109 prot./cm2, two orders larger as in LHC DIPAC 2005, B.Dehning

  33. Quench 7 TeV Current to Frequency Converter and Radiation Quench 7 TeV • Variation at the very low end of the dynamic range • Insignificant variations at quench levels DIPAC 2005, B.Dehning

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