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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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Considerations on ALICE BCM dump thresholds for RUN2

A. Di Mauro (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


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:


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


FILL 3220


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)


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


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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