BMLD refurbishing G. Iacobucci and G. Chiodini INFN Bologna and Lecce for the RPC group CERN, June 19, 2006 ATLAS Muon week

ATLAS muon week - June 19, 2006BMLD refurbishing - G. Iacobucci, G. Chiodini 2 Reason for this work:  Our RPC units have very small leakage currents (<<1  A).  This was achieved by requiring General Tecnica to install a c-shaped p.e.t. profile around the gas gaps. However, the early gas volumes were produced without this implemenent. These are 107 units out of the 116 which were mounted in 30 BMLD stations (26 double-unit and 4 single-unit stations)

ATLAS muon week - June 19, 2006BMLD refurbishing - G. Iacobucci, G. Chiodini 3 It was therefore decided to “refurbish” the 107 RPC units of the 30 BMLD stations by opening them and by: 1.installing the c-shaped p.e.t. profile around the gas gaps, to reduce almost to zero the leakage currents 2. installing a 14 mm wide aluminum tape on top of the c- shaped p.e.t. profile, to build an internal Faraday cage to further shield the strips against external noise (this implement was adopted for the BOL units and proved to be very effective)

ATLAS muon week - June 19, 2006BMLD refurbishing - G. Iacobucci, G. Chiodini 4 Overview of the work: It required a lot of hard work which involved many people: 1.Bring the stations to BB5 (Stephanie, Joerg + Logistics group) 2.dis-assemble a station (Frascati team) 3.uncable the two planes, separate the units (BB5 assembly team) 4.refurbish the units (“Refurbishing team”) 5.make a full test of the units (A. Salomon) 6.re-cable the planes 7.assemble back the station 8.pretest + test with cosmic rays... essentially all of BB5 ! The “refurbishing team”, Gabriele, Peppe, P. Giusti, Givi, Michele and R. Perrino thanks them all

ATLAS muon week - June 19, 2006BMLD refurbishing - G. Iacobucci, G. Chiodini 5 Work done on each unit: Once the “naked” units were available (thanks to the heroic effort of the BB5 assembly team which added this work to the usual heavy load they have and to the Frascati technicians) we proceeded in the following way: 1. take a test-pulse run (we dropped this test after few weeks, as we realized we did not produce damage to the units) 2. open the unit (… how many rivets!) 3. apply c-shaped p.e.t. profile and aluminum tape 4. check strip panels for dead channels (RF test) 5. re-built the unit (put rivets in position) 6. take a test-pulse run to check for dead channels 7. if ok: “close/fix” the rivets 8. flush and test the unit at 9.6 kV to hunt for dead channels by single rates and to measure the gap and leak currents.

ATLAS muon week - June 19, 2006BMLD refurbishing - G. Iacobucci, G. Chiodini 6 Criteria to accept an RPC unit We required:  in each strip panel: < 2 dead  strips and < 3 dead  strips  in each gas volume:gap current < 4  A/m 2 leakage current < 1  A The RPC unit was re-opened if these requirements were not met After we found all the small trapdoors preventing us from doing a high-quality job (special thanks go to R. Cardarelli), we managed to refurbish an average of two units/day with a team of 1-2 physicists and 2-3 technicians (top: 13/week) (although our Lecce + Bologna technicians rarely left BB5 before 8 p.m.)

ATLAS muon week - June 19, 2006BMLD refurbishing - G. Iacobucci, G. Chiodini 7 Results: leakage currents Essentially consistent with zero, for most of the units, except for ~10 gaps with ~0.3  A 4 gaps with 0.5 < i leak <1  A acceptance limit of 1  A

ATLAS muon week - June 19, 2006BMLD refurbishing - G. Iacobucci, G. Chiodini 8 Comparison before/after: Well within 1/10 of the first bin !

ATLAS muon week - June 19, 2006BMLD refurbishing - G. Iacobucci, G. Chiodini 9 Dead strips:  Number of dead strips below 1%, both  and   Same level as before We checked ~40000 channels 3 times.

ATLAS muon week - June 19, 2006BMLD refurbishing - G. Iacobucci, G. Chiodini 10 Conclusions That’s all folks