Resistive Plate Chambers for CMS (Pre-assembly Jobs done at BARC)

1. Resistive Plate Chambers for CMS (Pre-assembly Jobs done at BARC) Archana Sharma, Suman B.Beri P.U, Chandigarh & L.M.Pant BARC, Mumbai

2. Outline • Brief Introduction of the Work • Soldering of FRC connectors to adaptor cards of the FEBs • Soldering of signal cables to the adaptors • Leak test for gas-gaps – 9 nos (CERN) • Leakage current measurement of gas-gaps

3. Brief Introduction of the work done RPC- Resistive Plate Chambers: • The gaseous detectors of ionizing particles characterized by the large area coverage (~several m²), time resolution better then 2ns & space resolution of the order of cm. • Used for the muon trigger systems in CMS operated in avalanche mode. • Gas gap of about 2 mm is generated between the two bakelite sheets (each 2 mm thick) & a thin layer of graphite coating over its surface for uniform & intense electric field inthe gap.

4. The double layer consisting three gas-gaps • In the end-cap region of CMS, the RPC consists of a double gap arrangement Large gap (17357.6cm², 34715.2cm³ ) Medium gap (12445.75cm², 24891.5cm³) and Small gap (3921.9cm², 7843.8cm³). • The Cu read-out strips are sandwiched between the Large gap and the Medium and Small gap. • Whole system is packed inside a Honey Comb Panel.

5. Small Gap (3921.9 cm²) Medium Gap (12445.75 cm²)

6. Soldering of FRC connectors to adaptor cards of the FEBs • Interaction of charged particle with gases produces electric signal induced on the copper strips. • Signal is brought to adapter card by co-axial signal cables. • The FRC connector connected with adapter card goes to the input of the front end board/processing unit.

7. Contd…. • The Cu read-out assembly is divided into 3 sections. Each section contain 32 strips radially pointing towards the center of the end-cap. In total 96 read out channels for each RPC. • 16 channels from each section goes to one adapter card. Hence 6 adapter cards & 3 front end boards (FEBs) for each RPC. • The output of 3 front end boards goes through the twisted pair cable at the back panel of the RPC.

8. Contd……. • Soldering iron of 25 Watt (230 V) is used with 0.7 mm wire of lead free tin copper alloy for soldering adapter card with FRC connector. • On one adaptor card, there were 32 points to solder in which 16 points were for signal channels & 16 for ground channels. • Checked the continuity of each point on the adaptor card before & after soldering. • Also checked that there should be no shorting in the adjacent signal channels. • The adaptor cards were designed at NPD-BARC and were outsourced for production

9. Before Soldering FRC Connector Adaptor Card (signal side) Adaptor Card (ground side) After Soldering

10. Total number of adaptor cards after soldering – 80 nos.

11. Soldering of Signal cables to adaptors • First attached the ferrules to the both ends of the signal cable & then soldered these cables to the adaptor cards through the attached ferules. • Again checked the continuity on both signal side as well as in the ground side. • One end of the signal cable will go to the detector while the other to the adaptor card

12. Ferules

13. Gas Leak & Leakage Current test for gaps To check the leak in the gaps used in assembling the RPC detectors. Gas mixture for the leak test contains: • Argon : Using 20% in mixture. Kept the flow rate equal to 5 SCCM for leakage current test & 2 SCCM for gas leak test. • Isobutane : Using less then 5% in mixture. Kept the flow rate equal to 2.4 SCCM for leakage current test & 0.4 SCCM for gas leak test. • Freon : Using almost 75% in mixture. Kept the flow rate equal to 14.4 SCCM for leakage current test & 3.6 SCCM for gas leak test.

14. These gases pass through a Regenerative gas purifier and goes to the 4-channel gas mixer. • In the gas mixer, firstly these gases go in the solenoid valves & then to the mass flow controllers. • Solenoid valves operate by compressed air ( at 5 bar ).

15. In the 4 channel Gas – mixer there are8 flow controllers : 4 in sccm & 4 in lpm for the flow of gases Ways to use the mixed gases : 1)Online mixing 2)Premixing We are using the online mixing to use the mixed gas.

16. Purpose of Mixed gases: 1) Leak Test ( static pressure ) 2) Leakage Current test ( gases in flow mode) For the Gas leak test of gas mixture total flow rate : 6 SCCM the pressure in gap : 25-30 mm of water column above atm. pressure.

17. Leak test of gaps When there is a sufficient pressure of the mixed gas, valve is opened for the leak test. Mixed gas goes in three ways. 1) In the gap for leak test & the pressure with which the gas flows shown in the manometer by the difference in the two levels of a coloured red liquid (25 cm of WC for an hour).

18. Manometer for leak-tests at NPD-BARC Manometer Safety Bubbler Sensor

19. 2)Safety bubbler filled with silicon oil, to ensure that the pressure does not go beyond 50 cm of water column above atmospheres. Thus saves the gap from cracking. 3) Sensor Tested nine gaps from CERN. Results of the test shown in the table:

20. Leak tests for the bakelite gaps(RE*/3) CERN

21. Leakage Current Test for gaps • For the testing of leakage current, we require the mixed gases in a flow mode. • So after mixing the gases goes to 8-channel flow divider i.e. at a time we can test 8 gaps. Here we are using only six channels for six gaps. • Flow divider contains inlets & outlets for the gas. Exhaust gases goes to the atmosphere through a pipe.

22. Contd…… • Total flow rate is 22 SCCM for the flow of the gas mixture through six channels for six gaps. • This flow rate is sufficient for the 2 times change of gas volume in a day in all six gaps. • The inlet pressure of mixed gas going in these gaps is 59mb above atm.pressure where as the outlet pressure is 15mm of water column above atm.pressure.

23. Contd…… • Purging the gas mixture through all six gaps for two days. • Applied the High voltage in step of 1000V up to maximum limit of 9kV & noted down the variation of leakage current with voltage. • Set the maximum leakage current limit equals to 10 µA so that if for a given voltage leakage current exceeds this limit, voltage trips to zero. • Recorded the data for large, medium & small gap & plotted it.

26. THANKS