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Run Coordination R eport 4th RPC General Meeting (CMS week). Luigi BENUSSI, Hassan SHAHZAD, Nicolas ZAGANIDIS. RPC Operation overview. LHC achievements & plans Detector behavior Online P correction Operation performances Shifts Conclusions. LHC achievements.

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run coordination r eport 4th rpc general meeting cms week

Run Coordination Report4th RPC General Meeting (CMS week)


rpc operation overview
RPC Operation overview
  • LHC achievements & plans
  • Detector behavior
  • Online P correction
  • Operation performances
  • Shifts
  • Conclusions
lhc achievements
LHC achievements

Since the 24th of June new scheme : :50ns_1236b+1small_1180_37_1152_144bpi

lhc achievements1
LHC achievements

23:55 April 21st - world record for luminosity at a hadron collider with 4.67e32 cm-2s-1.

lhc plans1
LHC plans

Stay at 50 ns bunch spacing this year. Only next year go to 25 ns :

  • Now : Physics with 1236 bunches:50/pb-1 fill is the goal.
  • Physics with 1394 bunches
  • Decrease theemittances, populate the bunches
  • expected pileup rate : x ~3
rpc hardware status
RPC Hardware Status
  • Annual HV module recalibration – all CAEN A3512N HV module offsets recalibrated (125 Hvboards)
  • Number of RPCs operated in Single Gap mode is unchanged in 2011 for the endcap and increased from 6 to 10 for the Barrel:

Now : 10 in the Barrel and 19 in the Endcap

  • Number of disconnected chambers is unchanged in 2011 :

3 in Barrel & 3 in Endcap

….More details in the TC presentation…

barrel z dependence 2010 left vs 2011 right cms preliminary

Chamber behavior versus beam Luminosity

Barrel z dependence: 2010 (left) vs. 2011 (right, CMS PRELIMINARY)

Background rate vs Instantaneous Luminosity

For different Wheels (different position along z)

CMS preliminary 2011



The Current follows the beam luminosity No any abnormal behavior of the dark current has been observed

Peak Luminosity:

1.274x10*33 cm-2s-1

1.053x10*33 cm-2s-1

Dimon= 0.07 uA

RPCs ON cosmics

Beginning of the stable beams

End of stable beams




Dark current follows the

CMS Peak luminosity




The average RPC chamber current per wheel is lower than 2 µA for high luminosity beams except for W-2 which reached 2 uA

Stable operation, No any chamber with abnormal behavior observed

W-2 : 2.0uA

W0 : 1.5 uA

W-1 : 1.4 uA

W+2 : 1.8 uA

W+1 : 1.6 uA



Higher currents comparing to Barrel

Two disks reached 3 uA at the maximum instantaneous Luminosity

Stable Operation, no any chamber with abnormal behavior of the dark current

EP1 : 2.4 uA

EP3 : 3.uA

EN1 : 1.6 uA

EN2 : 2.8 uA

EP2 : 2.6 uA

EN3 : 3 uA

individual hv value setting for each channel optimizing the wp of each chamber
Individual HV value setting for each channel optimizing the WP of each chamber

In 2010 RPC system worked with 2 common HV

working points 9.35 kV (barrel) & 9.55 kV (Endcap)

We wanted to define the WP of each chamber in order to

  • improve the performance of the system by fine tuning the position of the WP in the plateau chamber by chamber :

i) avoid to stress the detector

ii) less sensitive to the small environmental changes

In 2010 not enough statistics to make a full efficiency scan

In 2011 RPC collaboration put a lot of effort in doing a full high voltage scan chamber by chamber in order to identify the best working point (WP) of each RPC roll and each HV channel taking into account efficiency , cluster size, Noise and trigger rate

…more details see DPG presentation ...

rpc average hit efficiency vs time

Next step :

  • Online Pressure correction of the Working Point
  •  1% efficiency fluctuation due to pressure variation
  • reduce the spread of the HV effective values
  • keep safe the detector
RPC average Hit Efficiency vs time



CMS preliminary 2011

CMS preliminary 2011

Average efficiency 94.9 ± 1 % (including all chambers)

Average efficiency 94.9 ± 1 % (including all chambers)






During running period:

  • Temperature is almost stable.
  • Big variation in pressure (typically in the range 945-975 mbar)

Algorithm- Flow diagram


Last Vbests applied ONLY whenever the ON command is released (squeeze)

Vbest -1

Vbest -1

Vbest -1

Vbest +10


  • No change whenever the sys is ON
  • Vbest calculated but not applied. Possibility to apply the new vbest resending On command.
  • Warning the operator in the rare cases a new correction is needed during the run


Manual ON












    • The Automatic Algorithm:
  • Vinitial
  • Enable/Disable correction
  • RoT = 1
  • RoP
  • Vbest
  • MaxVAllowed
  • MinVAllowed
  • CalcularionError



Ready but not applied


  • Values calculated automatically using the only P sensor available in UX
  • Granularity per chamber
  • New correction every 10-20 mins, ready to be applied

The Online P correction will be deployed in the next TA.New DOC duties : i) checking if not abnormal values of the HV that will be applied during the transition to SQEEZE ii) in SQEEZE checking that the HV applied values are conformal to the expected one iii) if DV >50 Volts (DP~5mbar) during stable beams apply the new Voltage (SMS warning) iv) CMS center : monitor the currents



i)For the physics fills the CMS shift leader will call the RPC doc at the beginning of the ramp. Latest one hour after the call the OM has to be in P5

ii) He has to check the distribution of the HV values that will be applied to the system. He wait until the transition to physics ( RPCs ON) and he checks that the applied HV correction is the expected one

iii)During stable beams :

if DV >50 Volts (DP~5mbar) one SMS warning will be sent to the RPC phone. The OM has to go to P5 check the distribution of the new HV values and send the command ON manually on the system.

DM + OM :

check the currents OFF line

Check the HV dustributions before & after the correction


No any significant RPC downtime & dead time during the last 3 months

Trigger L1-RPC : 0:04:02min/ 535 hours

A closer look to that 0% !....


Fault of LV LB power supply

Actually was a Trigger shifter fault!

3.3 pb-1 of BAD runs du to the HV scan over 700 pb-1


No any significant impact of the HV scan on the quality of the data

 We decided to do an HV scan per year

  • OM shift instruction manual on twiki needs to be updated.
  • To get the access rights in UXC, all the present and future OMs have to follow:

i)BioCell training course


ii) CMS level-4 safety module (online 40 minutes)

  • Follow at least the RPC weekly DPC &RC meeting.
  • OM Training sessions will be organized in near future.
run 2011 rpc shift
Run 2011 RPC shift

The present table contains the requested shift per institution. The shift are calculated considering 48 weeks of runs and 3 shifter per week (DOC, DM and CAF) plus 15% of contingency.

The request is to provide 2 shift(weeks)/EPS


August still 3 weeks are missing, september is empty :

 please book RPC doc shifts !!!

New OM shifters are welcome


No subscription fees!

Car and petrol are provided !

  • Low Dark currents and background rates are following the beam luminosity no any unexpected behavior
  • Fine tune of the WP improved the performance and insures more safe conditions for the detector
  • Online P correction of the WP will insure more stable operating conditions
  • Improve instructions & the shift organization