RPC HV efficiency scan

2011 HV scan SF6 flow-meter accident2011 Results2010-2011 comparison

RPC HV efficiency scan

Pigi Paolucci on behalf of RPC collaboration

Pigi - RPC project - XEB 12 April2

RPC – Why an HV scan ?

11/04/11

2010 pressureΔP = 20 mbar

2010 efficiencyΔε=10%

In 2010 we had not enough statistic to make a full efficiency scan

RPC system worked with 2 common HV working point 9.35 & 9.55 kV

RPC performance depends on P and T

We decided to do an HV scan per year: To define a WP per chamber in order to

improve the performance and avoid to stress the detector.

Choose a WP in the plateau region in order to avoid instability with pressure

RPC monitor stream is vital. Very high statistic in 1 hour at present L

RPC project - CMS GM 4 May 20113

HV scan – first 8 points 18-19 March: HV scan (8 points – HV corrected with pressure) 27 March: full analysis completed

About 60% of the rolls have a very good efficiency sigmoid fit – more points needed ! An overall efficiency decrease of 3% seen in the only run comparable with 2011 WP !!!

Pigi on behalf of RPC group

plateau curves repository

barrel barrel barrel

endcapendcapendcap

http://people.na.infn.it/~carrillo/rpc/0205111815/results/dataHtml.txt.html

http://people.na.infn.it/~carrillo/rpc/0205111815/results/dataHtml.txt.html

Pigi - RPC project - XEB 12 April4

HV scan – preliminary results

11/04/11

Defined plateau regionKnee 95%

Working = knee + 150 V

HV scan fit ε(HV) = εmax/(1 + eSlope (HV-

HV50%))

Working Point defined as Knee + 150 V taking into account the DP of 2010We can reduce to 100 in case of rate problem and even less when we will correct theEffective HV with the pressure variations.


HV scan – 11 points 15 April: 3 more points taken – scan completed (3.3 pb-1 BAD)

95% of the rolls have now a very good efficiency sigmoid fit


barrel barrel barrel

endcapendcapendcap


HV scan – Chi2 distribution


Chi2 sigmoid fit distribution


HV scan – all curves shifted it is now clear that was not an overall efficiency decrease but that all curves were shifted forward about 120 ± 10 V (respect 2010) ?? We double checked HV, pressure, temperature, timing, Trigger, m selection checked Everything seems to be ok – what about the GAS ?


Artificial shift of 110 Volts

2010


HV scan – curve shifted


HV scan 2010

Fit HV Scan 2011


HV scan – SF6 shift measurement 16 April: Gas expert called SF6 mass flow-meter replaced after few hours 18 April: System came back at nominal gas mixture

SF6 mass flow-control analyzed by Gas Group: not working properly - 30% more !!! 0.39% not 0.30% (flow-meter monitoring was stable and at 0.3%)

Only way to detect the failure was an external measurement with chromatograph 24 April: mini-scan in 2 sectors (39 rolls) to calibrate the shift due to the SF6


DHV (0.39% SF6 – 0.30% SF6) at 50% eff

HV50% shifted of 100 VoltsRMS is 19 Volts

100 Volts renormalizationwill be applied to all the curves


HV scan – working points 30 April:

Rolls WP merged in chamber and then in HV channel (1 HV ch. 4 bi-gap rolls) 2011 final HV working point table is ready (average of 4 rolls WP)

System should be now more stable .vs. pressure About 65% were working closer to the knee in the 2010


Nominalvoltage2010

Nominalvoltage2010

2010 DP

2011

2011

2010 DP

HV scan – final results I


2172 (99%) fits are good (51 recovered deleting 1-2 bad points) Only 23 OFF rolls are without plateau


All Barrel HV scan 2011

HV value at 50% eff

BarrelRMS 64 Volts

EndcapRMS 84 Volts

RPC project - CMS GM 4 May 201112 Pigi on behalf of RPC group


Cluster sizenoise

Public results on WEB page

HV scan – final results I


Also low efficiency rolls have a very nice plateau


barrel

1 Front End board broken

HV scan – final results II


2010

2011

Average Effective voltageover 1 month<9.35 & 9.55> kVPTcut > 0 GeV

Effective voltagein 1 hour9.35 & 9.55 kVPTcut > 7 GeV

Systematic errorof about 1%


ClusterSizeBarrel

2010

2011

Average Effective voltageover 1 month<9.35 & 9.55> kVPTcut > 0 GeV

Effective voltagein 1 hour9.35 & 9.55 kVPTcut > 7 GeV



Cluster size distribution at WP


• Cluster size distribution at the 2011 HV channel WP• Measurement will be re-done in 1 day after the TS

<CS> = 1.6RMS 0.23


HV scan – gas monitoring improvements

Central gas group is helping a lot in understanding the SF6 flow-meter failure and in improving the monitoring of this crucial component – Thanks

SF6 flow-meter is today monitored by the gas group with a gas chromatograph until the automatic procedure will be ready (June)”

RPC Gas system review 3 May (today): Gas Gain Monitor could be used to monitor the gas mixture

(under study) Gas monitor parameters alarm/warning have been reviewed Instructions for the RPC shifter will be updated



Conclusions


Barrel Gaps have been produced from 2003 and after 8 years Stability and uniformity of 2172 bi-gap rolls is now evident:

All the efficiency curve fits are good – 23 (1%) rolls are OFF Average efficiency ≈ 95% - stable in time (2010-2011) Efficiency RMS = 5% HV50% distribution has RMS = 64 Volts and 84 Volts (very uniform set)

HV working point table is now ready. It will be uploaded after TS Expected <efficiency> at WP are 95-96 % and more stable .vs. P & T

SF6 is a critical component for RPC detector 30% more corresponds to 110 Volts Gas chromatograph automatic measurement needed to control the gas mixture

Online HV correction with pressure is needed to reduce the operating voltage and keep safe the detector (under-study)

Final results WEB page

http://people.na.infn.it/~carrillo/rpc/hvscan2011_final_results/

RPC HV efficiency scan

Documents

Transcript of RPC HV efficiency scan