The concise status report on drift chambers (as of 12/12/2000). ---------------------------------------------- Here is a short description of what we were able to achieve/discover working on Brahms drift chambers for a few days in December. ====== T3 ====== - Two modules were dismounted and three loose wires were fixed. All of them were cathode wires. It looked like the wires slipped from the solder. We attribute these problems to statistics and do hope it won't repeat. - Having a gas mixture of Ar(60%)+Isobutan(40%) we were able to set 2100 V between anode and cathode. Rapidly increasing current inhibited setting higher voltages (in all modules, although the one which was not dismounted behaved slightly better, which may mean that 36 hours of gas flow is not enough to establish the equilibrium). A small amount of alcohol added to the mixture (~2.5%) significantly improved the performance. We were able to keep 2600 V in all modules with negligible current. - With a pulse generator we checked all electronics channels, carefully investigating those having problems during the last run. We found that the main sources of the problems were: 1) bad/loose connections of cables (especially ECL boards and low voltage cables) 2) bad TDC channels 3) no signals from the chamber (should be further investigated whether these channels can be recovered) Each problem causes distinctive effects in DC's performance, what helps to identify it. 1) and 2) are pretty easy to fix. 3) regards only less than a dozen channels in the whole T3 (out of ...). - We looked at cosmics triggering with coincidence in two adjacent CsI scintillators placed at the side of T3. From the rough on-line estimations of the detection efficiency it seems that above 2200 V we entered a plateau region. More accurate off-line analysis is in progress. ====== T4 ====== - All modules keep the voltages (up to 2200 V without alcohol). - T4 has been partially connected to multiplexers (we had 8 cards = 256 channels in hand, the rest is to be shipped to BNL in January). - We looked at single channels with a pulser - everything worked as anticipated. ====== T5 ====== - T5 is still waiting for cabling so we were only able to check whether it keeps high voltage. Modules 1 and 3 seem to be OK. Module 2 has a problem: there is a connection between a cathode wire and a field wire in one of the planes. Although the module can run as it is, the performance will suffer and the problem may develop in the future eventually disabling the module. Therefore it should be dismounted and fixed. TO DO list: - dismount and fix the middle module of T5 - check and fix possible connection problems (see description of T3 status) - test different characteristics of DC's (e.g. efficiency vs HV for different gas mixtures). Ideally this should be done under real working conditions i.e. with the beam, but tests with cosmics can provide valuable information as well. All this will be hopefully done around March. Best Regards, Jerzy Cibor and Pawel Staszel
This archive was generated by hypermail 2b29 : Wed Jan 03 2001 - 10:50:03 EST