April 13, 2011 Tracking CDC/FDC
Meeting Time and Place
Wednesday April 13, 2011 at 11:00am At Jefferson Lab, the meeting will be held in F326
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- FADC-125 Discussion
- FDC Update
- CDC Update
Participants: Curtis, Naomi, Gerard, Lubomir, Simon, Dave, Eugene, Fernando
Gerard presented some linearity tests that he had made with his preamp (configuration to be determined by Fernando) and the fADC125, the preamp showed considerable nonlinearity at half the ADC range. This raised the possiblity of doubling the ADC gain. The FDC cathodes show preamp saturation at about 80% of the ADC range so the FDC could use a gain increase of 20% but not 200%. Gerard suggested using 2 variants of the fADC.
CDC results with cosmics at CMU show nice separation from noise but the fADC values are 50% less than expected. There is a concern that increased noise in Hall D might hide the minimum ionizing peak but increasing the fADC gain will not change this. We would have to increase the HV and maybe use a quencher to suppress afterpulses.
Fernando would send Gerard more preamps (FDC and CDC versions) for linearity tests.
Fernando mentioned the temperature sensor on the preamps, he would like to remove it. After some discussion he decided to do some measurements to see how temperature-sensitive the gain is.
While Gerard indicated that it would be easy to have more than one version of the FADC125, Eugene was very reluctant to go this route.
The biggest concern at CMU is that since we are unable to utilize the full dynamic range of the FADC-125, our dE/dx capability will be reduced. There is a factor of about 30 from minimum ionizing to slow protons in the CDC. CMU was comfortable with the 12-bits we had, but it is now very important to understand what this dynamic range will be with the ASIC and FADC-125. We hope that Gerard's linearity tests can answer this at some level.
FDC and CDC updates
There was nothing astonishing to report so in view of the time we left these updates for next week.
After the meeting: it turned out that Gerard's preamp has lower dynamic range than the CDC preamp; it is also partly damaged so he would like to repeat the tests with the new preamps. Updated FADC scale info