1. 1 WP 10- High Voltage ’06 March 23 rd HV Trip studies  See previous meetings for the foreseen tests on LBC44  Started late by Clermont people when Clermont engineers were at CERN  Late availability of HV cable and Cooling  Instability of Cooling  Test stopped before the first night by Mohamed: No HV Trip during these 5 first hours  Tests continued later by David and Giorgi with a stable Cooling - On LBC44 (week end): 72 hours  No HV Trip - On LBC1 (next week end)  No HV Trip whereas trips (without air) were expected after a couple of hours Comment: Use of linear PS

2. 2  Request reminded since Meeting of March 2 nd  Compressor ready to work, but sniffer pipes not yet available  Proposition of using dedicated pipes for Commissioning with an easy handling  Recommendations  If the extraction of the LBC44 Super-Drawer was kept: - Made by Clermont team - in the presence of Clermont engineers  No HV Commissioning step without using the Compressor  First conclusions: - Confirmation of observations many times reported: strong dependence from the season (Winter/Summer environment) - But it would be wrong to conclude that it is the only possible explanation (see previous talks) - The action of extracting the Super-Drawer LBC44 to have a look inside should be reconsidered  this observed behavior does confirm the experience of experts saying that there will be nothing to look at!

3. 3 HV CANbus tests and Results Historical tests of the HV CANbus Results of CERN and Clermont tests Recommendations Proposed solutions for the near future ’06 March 23 rd Clermont-Ferrand team

4. 4 Historical comparison of the various set ups and test durations in the chronological order of the works Set up # of a full Daisy chain SiteCANbus PS CANbus Long cables? Daisy chain cables Drawer LVPS Test duration 1 Long term test of Opto cards Clermont No and FlatFlat 16 SDrawers 2001-2003 2 DCS testsClermont Long ATLAS cableFlat 16 SDrawers 2005 3 CERN testsATLASClermont Long ATLAS cable ATLAS then flat Some SDrawers Few days in 2006 4 Clermont tests Clermont Long ATLAS cable Flat then ATLAS 16 SDrawers Few days in 2006 5 CERN testsATLASClermont Long ATLAS cable? 16 SDrawers Not yet made  Summary of results: The ATLAS CANbus cable prevents a good working  Good working: Set ups 1, 2, 3 (Flat Daisy chain), 4 (Flat Daisy chain)  Bad working: Set ups 3 (ATLAS Daisy chain), 4 (ATLAS Daisy chains) the set up 4 being more complete (Drawers are supplied)

5. 5 Results of the tests 1. Tests of the HV side at CERN showed a not correct working of the CANbus for a certain number of Drawers (in both A and C sides, ≥12), and a strange stability over time (Stability OK after ~1.5 hour) but replacing the ATLAS CANbus cable by another one (flat in the tests) gives a correct working. 2.These results are completely reproduced at Clermont, but powering the 16 Super-Drawers enhances the bad working using ATLAS cables (Bad working> 4 super-Drawers, but long CANbus cable longer than in the pit of about 50 m) 3. Reducing the transmission speed from 250 Kbit/s to 125 Kbit/s gives a right working using ATLAS CANbus cables 0. It must be clearly known if the CANbus at the readout side works properly when the 16 Super-Drawers of a Daisy chain are all powered in the pit conditions

6. 6 Recommendations - The output voltage of the CANbus PS must be 20V when ATLAS will start (  Drop of ~4V in the long CANbus cable + Regulator specifications) Later, depending from the radiation accumulation effects, the voltage could be increased up to 24V.  Actions: - To come back to the first design of the CANbus PS - Comment: We were sorry to discover the changes made on these PS’s at the HV side … without a good knowledge of the HV electronics and forgetting to inform the Clermont responsibles who manufactured the CANbus PS - A Capacitor has to be installed at the first node of each Daisy Chain (A Filtering to prevent too big consumption when data are transferred, mainly due to the length of the long CANbus cable going to USA)  Actions: - Pull the corresponding Super-Drawer - Fix the Capacitor (inside a dedicated box) at the HV Micro card input

7. 7 Proposed solutions for the near future There are 2 possibilities: what is more painful ?  Playing with the inter-Drawer CANbus cables or with the Drawers ?  In any case, last tests must be made at CERN (Test 5), having all the Super-Drawers powered within one Daisy chain  Change of the cables Actions (mainly on LB) - Good choice of new CANbus cables - De-commissioning of LB then new cabling - Tests at ADC-I side and HV side  Change of the speed Actions (On LB, EBA and EBC: ~3 months with a good access) - Pull every Super-Drawer to access to the Speed switch of each Micro card - De-certification of each Super-Drawer with the risk of induced new failures - Tests to be made at least on the HV side (Clermont HV Test Bench) Warning: No use of MobiDICK (too big job) except if the Commissioning detects failures - New optimization of the HV DCS (  speed decreased) Just after Test 5 completion: A decision must be taken !