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July 31, 2014 FDC+CDC meeting


  1. DAQ (Beni)
    • Pedestals FDC and CDC pedestals as a function of time
  2. CDC status (Mike, Beni)
  3. FDC status [1], [2], [3], [4] (Lubomir)
  4. Electronics (Chris, Nick)
  5. Cathode scan deviation from nominal polsition1, polsition2(Luke)
  6. Other

Instructions for Bluejeans meeting connection

FDC meeting ID: 290664653


Participants: Sean (NU), Curtis (CMU), Eugene, Luke, Mike, Sergey, Dave, Chris, Nick, Simon, Beni, and Lubomir (JLab).


- Beni showed several results, explained in the logbook linked above. There are some fADC channels that don't report valid data (log entry 3290451). There's one module (ROCFDC3 slot 4) that was OK at the beginning of the run but at some point (after ~1k events) started reporting this problem for all of the channels.

- Typical CDC and FDC signals (from fADC) are shown in entry 3290447. The noise in the CDC is a factor of 2 higher than in the FDC (entries 3290447 and 3290445), also interestingly the frequency of the correlated noise in the CDC is a factor of 2 bigger. Lubomir: the CDC boards have 1/2 divider of the input signal, in contrast to the FDC. Would be interesting to check the noise without these resistors using also an FDC pre-amp.

- Beni found that there's some instability of the pedestals (3290411). For some of the channels there's even oscillation (3290403) with a period of about one hour.

- The plan is to have a synchronized (CDC&FDC + BCAL) run over the weekend.

CDC update

- Mike showed his studies of the noise (linked above). The burst noise (200kHz burst with 25MHz noise) disappears when turning off the HV of all/most of the channels. The other (white) noise doesn't depend on the HV. Mike showed possible sources of noise with a clock closer to 25MHz. For the FDC noise within the bursts is 12.5MHz.

- Noise discussions - Eugene: you should try with the cell repeater turned off. Beni: install some kind of copper mesh to shield the whole front of the CDC; the old FDC cathodes can be used for that? Sergey: try to shield the pre-amps with a box around them; some kind of pre-amp shield was already tried.

FDC update

- Lubomir: pictures attached show how the track through all the chambers was fitted: first using only cathodes fitting the avalanche positions (first plot). The residuals vs drift time (converted to distance) are correlated (second plot). Applying drift time corrections with already known (from the first fit) direction results in a line fit with chi^2/21 = 17/21 assuming 1mm error. If exclude the points for which the hits are very close to the wires, or at the edge of the cell, we get chi^2/14 = 6/14 which means resolution is about 650 microns.


- Chris and Nick worked on the bad 3M connectors. They opened and fixed several of them both CDC and FDC. The problem was that some signal wires were touching the shielding which is floating if not connected to the module. That's why we could see good signals with scope but not with the modules. Not all of the suspected 3M connectors were opened, only those that had wire to shield connectivity as checked with the tester.

- Retainer for the CDC pre-amps was designed and the parts ordered.

Cathode scan

- Luke did a second set of measurements in the middle of the cathode. First measurement was at ~13.5cm from the middle. The deviations from the nominal position, assuming a pitch of 5mm+12microns, are linked above for the two measurements. One can see relatively flat first foil (first 48 channels), then the middle foil has some some structures, then another pitch in the third foil. The overall deviations are +/-50microns. Better description can be obtained if assume 5mm +12/14/11 microns pitch for the first/second/third foil resp., then we have variations of +/-20 microns.