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Considerations on ALICE BCM dump thresholds for RUN2

Considerations on ALICE BCM dump thresholds for RUN2. A. Di M auro (CERN) LBS meeting, 16/06/2014. The Beam Condition Monitor system. Beam 1. BCM-A 8 diamond sensors z = + 6 m, r = 10 cm. Beam 2. BCM C 7 diamond sensors z = -18.5 m, r =10 cm.

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Considerations on ALICE BCM dump thresholds for RUN2

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  1. Considerations on ALICE BCM dump thresholds for RUN2 A. Di Mauro (CERN) LBS meeting, 16/06/2014

  2. The Beam Condition Monitor system Beam 1 BCM-A 8 diamond sensors z = + 6 m, r = 10 cm Beam 2 BCM C 7 diamond sensors z = -18.5 m, r=10 cm

  3. The Beam Condition Monitor system • The ALICE BCM readout electronics (CFC card + LHCb TELL1) integrates the signal over three Running Sums: RS1 40 ms, RS2 80 ms and RS32 1.28 ms • Initiates Beam Dump via BIS if signal is above threshold, delay for complete beam extraction is ~ 250 -290 μs • Rises Injection Inhibit flag to prevent further injection • Beam dump logic: • RS1 or RS2 coincidences: dump the beam if at least 3 adjacent diamond sensors show a current > thrRS1 or thrRS2 , respectively • RS32-Sum: Sorting out the two highest and the lowest of 8 sensors, dump the beam if RS32-Sum > thrRS32 • A dynamic threshold system is implemented in order to set high/low value depending on detector status (SAFE/READY) and beam modes:

  4. Luminosity jump on Dec 17, 2012 FILL 3457, 25 ns test, ADJUST: beams dumped by ALICE BCM due to luminosity,BCM RS32 (ALICE:BKGD3) just above dump threshold, all detectors were in stand-by → use BRANs to extrapolate collision rate

  5. FILL 3220

  6. ALICE Luminosity requirements for RUN2 Physics • Minimum bias~ 2∙1029 Hz/cm2 (rate ~ 15 kHz) • If bkgd rate >> collision rate → MB ~ 2∙1030 Hz/cm2 • Rare triggers ~ 7∙1030 Hz/cm2(rate ~ 500 kHz) • Max pile-up for RUN2: m = 0.01 Detector safety • The 8 gaseous detectors (TPC, TRD, TOF, HMPID, MCH, MTR, PMD, CPV) are protected against sparking by current trip thresholds in HV power supplies • High luminosity is equivalent to large currents in the HV-PS • Increasing current trip thresholds could weaken the protection in case of “diverging events” • Max tolerable rate:~ 700 kHz ~ 1 ∙1031Hz/cm2 • A too high luminosity would also induce ageing (beyond design specs)

  7. Luminosity vs separation • Luminosity in ALICE versus total separation of the 2 beams, 6.5 TeV. • Parameters: N=1.21011 p, e = 2 mm, b* = 10 m  s = 54 mm High dump thr. 7E31 Low dump thr. = 4E31 Limit 2s from target to dump J. Wenninger, MPP 16.05.2014

  8. Outlook • Use lumi-levelling with “intrinsic” soft protection • Implement in DCS detectors ramp-down on sudden luminosity increase (could be not fast enough) • ModifyBCM dump thresholds to avoid dumping on head-on beams → (dedicated study is ongoing, final results will be presented in September)

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