1. S.Colafranceschi 20 June 20111 1 Stefano Colafranceschi LNF Frascati CERN Universita’ di Roma – La sapienza An overview on gas studies, purifier materials and RPC chamber behaviour performed with a CMS scaled down gas system at the ISR experimental area e-Print: arXiv:1012.5511 [physics.ins-det] Presented by G.Saviano at RPC2010 - Darmstadt To appear on NIM

2. S.Colafranceschi 20 June 20112 CMS-PPC recirculation gas system “closed loop” The large detector volume (18 m 3 ) and the expensive gas mixture make a closed loop recirculation system mandatory. In the CL system, gas purity is guaranteed by a multistage purifier system. Purifier 1 consisting of a 24-litre cartridge filled with 5Å Type molecular sieve manufactured by ZEOCHEM Purifier 2 consisting of two 24-litre cartridges, each filled with a combination of: 1. 25% Cu-Zn filter type R12 manufactured by BASF 2. 25% Cu filter type R3-11G manufactured by BASF 3. 50% Ni AlO3 filter type 6525 manufactured LEUNA A systematic investigation was proposed aimed to fully clarify the presence of pollutants, the chemistry of purifiers used in the CL, and the optimized regeneration Goals are Confirm currents increase is only in TOP (upstream) gaps and not in DOWN (downstream) gaps Measure lifetime of unused purifiers, observe RPC currents rising, identify contaminant(s) in correlation with the increase of currents Repeat objective b) with regenerated purifiers

3. S.Colafranceschi 20 June 20113 RPC GAP DOWNSTREAM GAP UPSTREAM GAS INPUT GAS OUTPUT Double gaps RPC

4. S.Colafranceschi 20 June 20114 Closed loop setup Closed Loop (CL) prototype test system area, for testing performance of CMS gas recirculation system, purifiers and identification of contaminants 1.The Closed Loop (CL) prototype test system area, is testing performance of CMS Resistive Plate Chambers, gas recirculation system and purifiers (identification of contaminants). 2.CL TEST is equipped and monitored with: GasChromatograph, Temperature/ Humidity/ Pressure sensors, mixer and gas flow monitoring, chemical setup 3.In the experimental area 11 double gaps RPC are installed (9 in recirculation mode, 2 in open mode).

5. S.Colafranceschi 20 June 20115 Chemical Analysis setup Bottles have been collected (ready to be analyzed) flown during period with high currents. We expect to find pollutants inside flasks and on the pre-filters Sampling points : HV61: before filters HV62: after zeolite HV64: after Cu/Zn filter HV66: after Ni filter Sampling the closed loop gas, before and after each purifier. The sampled gas bubbles inside a LiOH solution continuously in order to collect contaminants.

6. S.Colafranceschi 20 June 20116 The Environment: RPC are very sensitive to environmetal: this study has been performed in environmental controlled room Temperature ( ‘ C) Relative Humidity (%)

7. S.Colafranceschi 20 June 20117

8. 8 Conclusions 1.System in run since two years 2.Observed currents increase in upstream RPC gaps, downstream gaps are stable 3.filters lifetime with new materials is about six months 4.Observed contaminants in gas in correlation with currents increase K and Ca increase in gas when currents increase, t K and Ca increase in gas when currents increase, t he sampling point HV66 (after the filters and before the gaps) shows a large increase in K during cycles 3 and 4 this could account for current increase in the gaps gas gas mixture (due to the presence of HF) tends to release these elements from zeolite framework. Fluorine is constantly produced during the flux and the zeolite traps it efficiently. Further studies are in progress to fully characterize the system

9. S.Colafranceschi 20 June 20119 9 References G. Saviano in behalf of CMS collaboration; “Materials, Filters And Gas Analyses For CMS RPC Detector In Closed Loop Test Setup” Workshop RPC Mumbai 2008 S. Bianco in behalf of CMS collaboration; “Chemical Analyses Of Materials Used In CMS RPC Muon Detector”. LNF-09/18(P) 1.Run in progress with regenerated purifiers to measure lifetime, end by mid July 2011 2.Confirming requests submitted in 2010 to Mar: 1.Repeat this study in high-radiation environment at GIF 2.Test Optical sensors for HF at GIF Outlook