Revision as of 19:11, 19 March 2015

March 19, 2015 FDC+CDC meeting

Connection

1. Instructions for Bluejeans meeting connection
2. FDC meeting ID: 290664653
3. To join via a Web Browser, go to the page [1] https://bluejeans.com/290664653.

Agenda

1. Gas issues
   • FDC gain measurements [2], [3], [4], old measurements
2. CDC update (Beni, Mike)[5]
3. FDC update
   • Fluorinert leakage on 03/09, on 03/18
   • no corrosion [6] (Lubomir)
4. Electronics: logbook entry 3325323, 3325070 (Fernando, Cody, Chris, Nick)
5. Engineering (Dave)
   • CO2 sensor pump
6. Other

Minutes

Participants: Naomi (CMU), Sean (NU), Fernando, Dave, Chris, Nick, Beni, Sergey, and Lubomir (JLab).

Gas issues

- Lubomir presented summary of the FDC gas gain measurements with 55Fe source: first plot shows charge distributions at different HV in the Hall, package 4. Second plot is a summary of all the measurements at 2200/-500V both in the Hall and in the EEL126 with the spare package, as a function of the atmospheric pressure. 1% change of the pressure results in 5-7% change of the gain, as expected from the literature. By some reasons the charge on the upper strips is bigger than on the down ones for both measurements in the EEL and in the Hall; needs further studies. Third plot shows the gain-HV dependence at fixed (+/- 0.2 kPa) atmospheric pressure from the measurements and also from Garfield simulations. Garfield predicts somewhat stronger dependence: Sergey explains it with space charge effects at higher gains when using 55Fe source. Assuming a mixture of 45/55 Ar/CO2 (plus 0.3% alcohol) in the Hall Garfield predicts higher gains than what was measured in the Hall, all this relative to the standard gas mixture 40/60 in the EEL. A simple explanation might be a difference of the gas temperature in the Hall and in the EEL: 6 degC lower temperature in the Hall will explain it, or 1% (absolute) change of the CO2. Conclusion: generally the gain measurements in the EEL and in the Hall are in agreement with a change of the CO2 from 60% to 55% (+/-1%). Last plot shows previous gain measurements for four gas mixtures using different techniques.

- Beni continued changing different configurations in the gas mixing system trying to identify the source of the disagreement without success so far: the biggest change in the max drift time was 8% but was not repeatable.

CDC update

- Mike showed a plot with the positions of the noisy channels: most are at ~7 o'clock. The HV filter was installed on the channels at ~9 o'clock and this sector is indeed very clean.

FDC update

- The chiller is consuming a lot of Fluorinert. After 10 days of operation we had to refill it with ~1.5 galons.

- Today we did (together with Dave and Casey) a small modification in the spare package. We used the opportunity to look at the cathode: as seen from the picture above, there are no hints for corrosion in the place where the O-ring goes over the connector traces. The spare package was sitting in EEL126 for two years.

Electronics

- Beni checked the fADC crates with pulser (Mike's code) and found ~10 bad channels in the FDC. 6 of them had some connector issues and were fixed by Chris and Nick, 4 are still bad (first log entry).

- Lubomir looked at the data (first runs after the chiller was installed) and made a list of bad channels (second log entry linked above). There's nothing new or unexpected, these are 0.6% of the total channel number. Noticeably, there are 8 new bad wire channels sitting on one ASIC in the pre-amp. Fernando wanted to have a code, similar to the one for the fADCs, to check the TDCs with a pulser. Bryan has implemented already this feature in his libraries.

- Beni: one FDC crate (rocfdc9) is crushing from time to time, he suspects broken SD.

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