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

DIPAC 2005, B.Dehning 2 Beam loss measurement design approach Damage (system integrity) Quench (operational Efficiency) Scaling: frequency of events x consequence Failsafe Redundancy Survey Check Mean time between failures Methods: Stop of next injection Extraction of beam Reduction of operational efficiency Safety Protection Risk Availability SIL ALARP Systems: Beam loss Monitors Quench protection system Interlock system ¨ Dump system Design issues: Reliable components Redundancy, voting Monitoring of drifts to /h

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 LHC Bending Magnet Quench Levels LHC quench values are lowest (values proportional) DESY 2.6 – 6.6 E-03

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: 1.in case of system failure dump beam (failsafe) 2.verification of functionality: simulate measurement and comparison with expected result

DIPAC 2005, B.Dehning 8 Role of the BLM System for the protection SOURCES of beam losses 1.User/operator 2.PC failures 3.Magnet failures 4.Collimators failures 5.RF failures 6.Obstacles 7.Vacuum 8.… HERA Tevatron, LHC Dump system Interlock system Dump requests

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

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, N 2 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 N 2 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 Energy deposition (LHC) Beam scanned Signal vs voltage (SNS)

DIPAC 2005, B.Dehning 13 Ionisation chamber currents (1 litre, LHC) 450 GeV, quench levels (min)100 s12.5 nA 7 TeV, quench levels (min)100 s2 nA Required 25 % rel. accuracy, error small against 25% => 5 % 100 pA 450 GeV, dynamic range min., used for tuning 10 s10 pA 100 s2.5 pA 7 TeV, dynamic range min.10 s160 pA 100s80 pA

DIPAC 2005, B.Dehning 14 Gain Variation of SPS Chambers 30 years of operation Measurements done with installed electronic Relative accuracy < 0.01 (for ring BLMs) < 0.05 (for Extr., inj. BLMs) Gain variation only observed in high radiation areas Consequences for LHC: No gain 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: Actels 54SX/A radiation tolerant. Communication links: Gigabit Optical Links. Surface FPGAs: Alteras Stratix EP1S40 with 780 pin.

DIPAC 2005, B.Dehning 16 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, p/s/cm 2 ) Bipolar Customs ASICs Triple module redundancy Reset timeIntegration time V out I + I - Threshold Comparator 100 ns100 ns to 100 s

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 FNALLHC channels416 Time resolution 21 s40 s # of running sums 311 windows 21 s to 1.4 s 80 s to 84 s thresholds412 Synchronized to machine timing yesno post mortem buffer 4k values 1k values

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 Beam loss measurement design approach Damage (system integrity) Quench (operational Efficiency) Scaling: frequency of events x consequence Failsafe Redundancy Survey Check Mean time between failures Methods: Stop of next injection Extraction of beam Reduction of operational efficiency Safety Protection Risk Availability SIL ALARP Systems: Beam loss Monitors Quench protection system Interlock system ¨ Dump system Design issues: Reliable components Redundancy, voting Monitoring of drifts to /h

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 LHC transmission check Signal Select Table CRC32 checkComparison of 4Byte CRCs OutputRemarks AB Error DumpBoth signals have error Error OKDumpS/W trigger (CRCgenerate or check wrong) ErrorOKErrorSignal BS/W trigger (error at CRC detected) ErrorOK Signal BS/W trigger (error at data part) OKError Signal AS/W trigger (error at CRC detected) OKErrorOKSignal AS/W trigger (error at data part) OK ErrorDumpS/W trigger (one of the counters has error) OK Signal ABy default (both signals are correct) 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. Tunnels 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. Most false dumps initiated by analog front end (98%) because: 1.Reduced check 2.Quantity 3.Harsh environment Highest damage probability given by the Ionisation chamber (80%) because: 1.Reduced checks 2.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 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 Response of ion chambers for different particle species u+ u- Gamma e+ e- pi+ pi- neutron proton Due to attenuation of shower => increase of non linearity of chamber response

DIPAC 2005, B.Dehning 30 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 Quench level and observation range 450 GeV 7 TeV Dynamic Arc: 10 8 Collimator: Damage levels Arc 2.5 ms Special & Collimator 1 turn BLMS* & BLMC

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

DIPAC 2005, B.Dehning 32 Ionisation Chamber Time Response Measurements (BOOSTER) Chamber beam responseChamber current vs beam current Intensity discrepancy by a factor two Intensity density: - Booster prot./cm 2, two orders larger as in LHC FWHM e- = 150 ns length proton = 50 ns 80 % of signal in one turn

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