Winter shutdown 08/09 Summary of HV interventions Barrel Muon Workshop, 02/09 Jesús Puerta-Pelayo, CIEMAT 17-February-2009

Jesus Puerta-Pelayo, CIEMAT MUB Workshop Feb/09 2 By the end of November, when the detector was opened, 15 chambers with HV problems, some of them for months. Interventions in all of them had been scheduled. All problems had been bypassed by means of TJBs (towers), several pins disconnected. Mostly strip problems, wire to ground, few cathodes HV status as of November 08

Jesus Puerta-Pelayo, CIEMAT MUB Workshop Feb/09 3 Three possibilities: –Full extraction –Intervention on extraction tool –On site HV status as of November 08

Jesus Puerta-Pelayo, CIEMAT MUB Workshop Feb/09 4 After reconnecting pins in TJBs by beginning of December, most of problems gone (8 out of 15) Back from the dead + 1 additional problem YB+2 (it disappeared later)

Jesus Puerta-Pelayo, CIEMAT MUB Workshop Feb/09 5 Reconnection: problem no longer there. Sometimes problem disappear by themselves (probably dust/dirt displaced by the gas flow) In some other cases, currents still there but can be cured: – The overcurrent limit is set to 2 uA: increasing it by hand while keeping and eye on the induced currents ‘burns down’ the problem inside the cell in a short time.. Still a problem in MB4S02: some mid-height discharges with low frequency (1/minute at most). Very difficult to identify and fix (several days needed with chamber extracted) Revived chambers

Jesus Puerta-Pelayo, CIEMAT MUB Workshop Feb/09 6 We ended up with a final list of 5 chambers to be intervened. Positive end was opened first, YB+2 was used to support the beam pipe flange. The presence of the beam pipe made maneuvers more complicated –Forbidden to work or move heavy material over the pipe –Chamber rotations too tight Most complicated interventions in YB0 (no access), Extractions in YB0 must be done from the FE side (that implies uncabling, removal MABs and cable trays, retract and secure ECAL LV cables, etc. For the rest of wheels, phi SLs can be intervened in place. Theta SLs using extraction tool. Interventions timeline

Jesus Puerta-Pelayo, CIEMAT MUB Workshop Feb/09 7 HV interventions YB+1, YB+2 YB+2 HV side was accessible for a couple of days before YB+1 was moved, we profited and did the first intervention on December 5th (+2/1/08, no extraction needed, intervention on phi SL), one disconnected cathode. When YB+1 was moved close to YB+2, we accessed HV side of +1/2/01. Intervention performed on December 11th (no extraction needed, intervention on phi SL), one disconnected cell. First intervention in vertical position

Jesus Puerta-Pelayo, CIEMAT MUB Workshop Feb/09 8 YB0 HV interventions Sector 3 in YB0 freed for intervention on 0/4/03 (fixed services in HV side), full extraction required, Retracted EB cables Chamber posed on the ground: one cell disconnected. Certified after intervention using Franco’s portable cosmics system

Jesus Puerta-Pelayo, CIEMAT MUB Workshop Feb/09 9 YB0 HV interventions (II) Two more interventions on YB0, in these cases using the extraction tool (theta SL) 0/3/06 (11 Dec): External discharge (inside gaseous volume). Bad isolation fixed 0/2/09 (22 Jan): Internal discharge, one cell disconnected. Not the easiest position, but it’s proven to be feasible

Jesus Puerta-Pelayo, CIEMAT MUB Workshop Feb/09 10 YB-2 HV interventions Last intervention, also on extraction tool (-2/1/08, on 22/January, one extra dead channel) Complicated position due to presence of the nose and endcap feet (1 scissor lift + 1 cherry picker)

Jesus Puerta-Pelayo, CIEMAT MUB Workshop Feb/09 11 Statistics: – Disconnected channels TJBs before interventions: 26 HVBs (208 cells) –After retesting and reconnections, remaining problems: 13 HVBs (104 cells) –Additional disconnected channels after interventions (internal discharges) = 4 cells + 1 cathode 100 drift cells recovered thanks to interventions! What did we gain

Jesus Puerta-Pelayo, CIEMAT MUB Workshop Feb/09 12 Also several chambers with gas problems have been checked during interventions: –YB0 MB4 S06: different between output/input flows of 25%. A defect was found in the sealing o- ring of output line quick connector –YB0 MB4 S04, bad timeboxes, only one SL. Our suspect was a blockage in the input manifold. After exchanging of input/output lines, data look fine now. –Two more chambers are kept in open loop (bubbler) due to structural problems: -2/3/01, -1/4/12 The gas saga

Jesus Puerta-Pelayo, CIEMAT MUB Workshop Feb/09 13 In general HV interventions have been quite satisfactory (less than expected, all of them successful). YB0 interventions less dramatic than predicted (uncabling/cabling quite fast), space is tight but the installation team is well experienced. Tried several positions of the extraction tool, successfully. Not possible to carry out interventions in upper sectors of moveable wheels in the current manner (specially +-2) due to presence of beampipe. We’ve been lucky identifying problems ‘by eye’, but it may not be always like that… Transparent covers for HV problems? Conclusions and caveats