TOF status and LS1 plans

27/06/2012

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① Review current detector issues

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1. What are the current hardware problems that create data taking inefficiencies and what is the planned follow up ?

The major source of data taking inefficiency due to the TOF detector is the issue with the 3.3V (100A) LV channels. This failure (Under Voltage) can be recovered with a power-cycle; nevertheless, if TOF is running, it will make the run crash.

• this problem started happening during last year;• 13 events have been recorded since April 2012 (affecting 11 crates) randomly distributed over the TOF;• no obvious correlations with beam conditions, TOF status and data taking activity (details in backup

slides). We have already checked LV settings and threshold; could they be induced by other detectors activities (via ground connections)?

CAEN is investigating the problem since the end of 2011. One full crate (3 times in error in December 2011) is currently under test in Viareggio.

Backup solution: use the DAQ pause-and-configure procedure.

• FW with SYNC event handling already deployed (tested OK);• Recovery procedure has to be implemented: PVSS (crate rebooting - Andrea) + VME (data taking

resuming without a SOD - Pietro). Possible, even not trivial.

TOF issues

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2. Which are the rate limits of your detector and what are the detailed reasons ?

No any problem with the expected rates at the predicted 2012 pA luminosities are foreseen with the TOF detector (see next slides).

TOF issues

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PbPb @ L = 4×1026 Hz/cm2 (estimated V0AND ≈ 200kHz) ITOF ≈ 80μA.

TOF load due to background events is less wrt genuine pp collisions. To estimate the TOF expected behavior with pPb in 2012 we should extrapolate the PbPb values.

For pPb @ 200kHz we would expect that ITOF ≈ 3 ITOF(PbPb @ L = 4×1026 Hz/cm2 ) ≈ 300μA less than 0.2μA per MRPC.

Since the average dN/dy is 360 for PbPb and 21 for pPb, we can assume that the detector load for pPb (@200kHz) should be 200kHz/4kHz * 21/360 ≈ 3 times the detector load observed with PbPb in 2011.

gap of 4.5uA due to a single faulty chamber

TOF in the pPb 2012 scenario

negative HV positive HV

pp @ V0AND ≈ 260kHz ITOF ≈ 50μA.

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PbPb @ HL LHC (L = 5×1027 Hz/cm2)

pPB 2012 (L = 1029 Hz/cm2)

The MRPCs demonstrated to tolerate fluxes up to 1kHz/cm2 without problem.

MRPC rate capability with PbPb extrapolated to pPb 2012Measured flux of particle scales linearly with the luminosity (the flux has been estimated using the single trigger-pad rate and the ratio between trigger-pad and readout-pad multiplicity). The expected flux with pPb and a value of L = 1029 Hz/cm2 is ≈ 25 Hz/cm2.

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Saturday, 16th June 2012, the ALICE solenoid tripped; this resulted in an increase of the vacuum pressure in the beam pipe inside the ALICE hall. The large amount of beam-gas interactions induced an increase of the current drawn by the TOF detector.

ITOF = 560uA @ V0AND = 2MHz

From PbPb extrapolation we would expect ≈ 830μA @ 2MHz of V0AND instead of 560μA, which is the measured values; the genuine pp collisions equivalent load could be estimated as ≈ 1.3MHz, far in excess of the expected values for pPb 2012. By the way, the total current drawn by the TOF for this very high load value was less than 0.4μA per MRPC.

When ITOF > 1mA the TOF HV channels started tripping just because the Imax threshold is at the level of 20μA per channel (10μA for both negative and positive channels) ≈ 1μA per MRPC.

Unplanned test @ high rates

V0AND = 3MHz

negative HV positive HV

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② Plans for LS1

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1. review of the cooling system -- are there upgrades and improvements necessary ?

No urgent upgrades are needed.

• As a low priority improvement, it could be useful to have a tool to tune the pressure in each individual cooling loop (3 + 3 loops for crates and 3 + 3 loops for FE).

• Actually we are sharing our cooling plant with PHOS and EmCal; are some changes foreseen?

LS1 plans – cooling system upgrades

average crate temperature

average crate temperature

FE electronics board temperature

upper hemisphere

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2. review of the gas system -- are there upgrades planned ? Can we reduce the gas consumption ?

No upgrade are planned, no gas consumption reduction until the end of 2012 data taking.

During the LS1 we agree to reduce the gas consumption:

• by stopping the gas system and flushing the TOF only for short periods every few months;

• we don’t want to use gas mixtures different from the one used so far during data taking.

However we want to start flushing the TOF with the standard gas mixture and with high fluxes at least 3 months before the resuming of the data taking after LS1.

LS1 plans – gas system upgrades

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3. are the new cable to be pulled between the CRs and the cavern for your subdetector ?

The answer should be “No”, but…

… we observe that some LV PS failures can be recovered switching off completely the PS (CAEN A3485A). In the present design we have 4 power supplies (1 per corner) each one providing the 48V service to 9 A3485A (one A3485A gives power to 1 pair of crate). To recover one crate we have to switch off a quarter of TOF (not recommended with B filed ON).

We ask CAEN to develop a solution in order to distribute the 48V service so we can switch off each A3485A leaving the others on. We are still waiting a few details from CAEN concerning:

• how this solution will be implemented from the hardware point of view (external board or embedded solution);

• how we can control each individual 48V service lines (by software with the A1396A branch controller already used to control the A3485A power supplies or with dedicated boards to be housed by crates in the CRs). In the latter scenario we will need to pull some cables between CRs and the balcony

A technical report from CAEN is expected for this or next week.

LS1 plans – pulling new cables

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4. what kind of hardware interventions are planned ?

• Full replacement of all CAEN DC-DC converters (A1396A); so far 5 final-version A1396A have been installed (during 2012 TS1) and are working without showing any problem.

• Replacement of faulty DRMs (Detector Readout Module), TRMs (TDC Readout Module) and LTMs (Local Trigger Module).

• Improving of the ground connections;

• Intervention (eventually) on the cooling system, at the crate level, for two very hot crates in sector 08.

It would be very useful for us to have a time schedule of the working periods in order to plan the activities with our technicians.

LS1 plans – hardware interventions

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backup

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date crate TOF status (since) LHC mode (since) TOF DAQ status (time since 1st physics run)

V0tot rate

Notes

11/09 16 New A1396

13/09 39

14/09 67 New A1396

28/09 66

04/10 25 New A1396

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18/10 42

28/10 08*

24/11 42*

27/11 15

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03/12 43

08**

05/12 42**

3.3V failure in 2011

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date crate TOF status (since) LHC mode (since) TOF DAQ status (time since 1st physics run)

V0tot rate

Notes

12/04 33 READY(1h 45m)

STABLE BEAM(1h 45m)

Not Running(1h 20m)

100 kHz

7 READY(2h 34m)

STABLE BEAM(2h 34m)

Running PHYSICS(2h 11m)

100 kHz Run stopped

19/04 67* BEAM_TUNING STABLE BEAM(3h 38m)

Not Running ??? New A1396

20/04 58 BEAM_TUNING STABLE BEAM(2h 6m)

Not running 620 kHz New A1396

7/05 57 READY(1h 13m)

STABLE BEAM(1h 19m)

Running PHYSICS(1h 3m)

103 kHz Run stopped

31/05 62 BEAM_TUNING STABLE BEAM(1h 46m)

Running TECHNICAL 500 kHz

08*** BEAM_TUNING STABLE BEAM(5h 25m)

Not running 300 kHz

03/06 15* READY(12h 20m)

STABLE BEAM(19h 51m)

Running PHYSICS(11h 10m)

??? @ SOR

04/06 33* BEAM_TUNING STABLE BEAM(1h 4m)

Running TECHNICAL 457 kHz

07/06 65 BEAM_TUNING STABLE BEAM(7h 53m)

Running TECHNICAL 250 kHz @ SOR

3.3V failure in 2012 1/2

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date crate TOF status (since) LHC mode (since) TOF DAQ status (time since 1st physics run)

V0tot rate

Notes

15/06 29 BEAM_TUNING STABLE BEAM(4h 5m)

Running TECHNICAL 350 kHz

18 BEAM_TUNING STABLE BEAM(18m)

Running TECHNICAL 415 kHz New A1396

18/06 58* BEAM_TUNING STABLE BEAM(2h 10m)

Running TECHNICAL 440 kHz New A1396@ SOR

3.3V failure in 2012 2/2