Results from the CMS-RPC tests at CERN Gamma Irradiation Facility Roberto Guida CMS-RPC (Bari, Beijing, Napoli, Pavia, Sofia) Seoul, October 2005

Overview Aim of the test The history up to now Current items:  Performance vs. aging  Gas studies (HF production) (see my Monday talk)

Aim of the test Check the RPC performance after a working period equivalent to 10 CMS years possible long term effects of the close loop gas system on the chambers performance HF and others pollutants production and their effects on the chambers performance

The history up to now Two sets of chambers: “Small” and “Big” 11 gaps2 final chambers (RB1) Endcap RPC RE1

History of the “small” Dimensions: 50 x 50 cm 2, equipped with 10 x 10 cm 2 pads Entered in the GIF during May 2002 Integrated charge up to now: 70 mC/cm 2 Equivalent to ~ 15 CMS years (safety factor included) Always on the open loop gas system, at first with dry mixture, then with moist mixture

Integrated charge “Small” RPC

“Small” RPCs 11 RPC (50 x 50 cm 2 ). Series circuit: 1 double oiled RPC 4 oiled RPC 2 no oiled RPC Parallel circuit: 3 oiled RPC 1 no oiled RPC Used gas mixture: 96 % C 2 H 2 F 4, 3.5 % iC 4 H 10, 0.5 % SF 6

These chambers have passed… Major problem with copper springs new spring used spring silicon hose

Major problem with copper springs: Followed by a strong increase in current and counting rate From May to Sept 2002

…more … T-connectors in the gas circuit badly damaged by HF in exhaust Detail of a T-connector with an evident “corrosion” effect on the internal surface Problem solved moving to connector made of polycarbonate

… and more... Frequent detector displacements in GIF  problem in gas distribution and worst

…nevertheless … Present performance RPC - 3 Final efficiency at ABS 0 (Source Off), ABS 1 (Full source), ABS 2, ABS 5

Present performance RPC - 9 Final efficiency at ABS 0 (Source Off), ABS 1 (Full source), ABS 2, ABS 5

Performance vs aging Working voltage at 90% efficiency as a function of the time for ABS0 (Source Off) and ABS1 Last test

Rates at 9.8 kV and ABS1 Recovery of RPC9 with the moist mixture: maximum efficiency vs time at Source Off and ABS1 Last test

… in addition… These chambers have been used to understand HF production in RPCs: two important results: HF seems to be proportional to operating HV and to gamma irradiation Most of the produced HF reacts (remains) inside the chambers

“Big” chambers Actual production RB1 chambers At the beginning: CH25 and CH26, open loop mode; until December 2003 integrated 15 mC/cm 2 ~ 3 CMS eq. years Then CH25 died and was substituted by CH45 CH 26/45 have integrated with the closed loop gas system about 30 mC/cm 2 ~ 6 CMS eq. years

Experience with the Closed Loop Characteristics of the system: 5 lines for the closed loop 2 lines for the open loop Total of 2 chambers connected: Barrel: 26,45 Chromatograph + PC readout Gas monitor PC The rack

Experience with the Closed Loop Exchange rate: 1 volume/h Humidity: ~50% (except the first period at ~40% R.H.) From beginning of February 2004: gas system running continuously at 95% recirculation Several kind of techniques for monitoring the mixture quality: 1.µGas Chromatograph (Allows an immediate feedback on the gas, but low sensitivity) 2.“CERN” analysis (A complex and long procedure to take samples; results after some time) 3.“Roberto” analysis (Use the same procedure to take samples, allows a good resolution) 3 filters used: molecular sieve, 50% Copper, Nickel

Integrated charge “Big” RPCs

The problem with CH25 Steady current increase The reason: chamber slightly leaking (about 1 l/h on 20 l/h total flow, 1.5 l/h new gas mixture), not found at the beginning and not so easy to detect Chamber opened (bakelite surface analyzed, some results were presented on Monday) Following these observation, much more care has been put in gas leakage test for production chambers, and some of the rejections were found to be related to this problem

Present performance Chamber 26 efficiency at ABS0 and ABS1 (single gap and double gap)

Noise rate at Source Off Cluster size at different irradiation factor Noise and cluster size for CH26 are compatible with the results obtained during the production test After ageing test

Cluster size vs Irradiation RPC working point at different irradiation conditions Cluster size at 90% and 95% in different source conditions

RPC 26 current at Full source

Increasing of the ohmic current and rate off in RPC26 due to a low gas flux RPC 26 gas problem Noise rate

Chamber 45 efficiency at ABS0 and ABS1 (single gap and double gap)

Noise rate at Source Off Cluster size at different irradiation factor Noise and cluster size also for CH45 are compatible with the results obtained during the production test After ageing test

Chamber 26 double gap efficiency and cluster rate at ABS0, ABS1, 2 and 5

Chamber 45 double gap efficiency and cluster rate at ABS0, ABS1, 2 and 5

down up Efficiency (%) double Chamber RB1-26: comparison between June 03 and June 04

Conclusions Both the two sets of RPCs (Small and Big) have a good efficiency (rates and currents are normal) as shown by the final results of the last test beam an integrated charge equivalent to about 6 CMS years has been accumulated in the close loop gas system however, taking into account also the first test period (open loop gas system) an integrated charge equivalent to about 9 CMS years has been accumulated