CountingDaq 220218

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Meeting information

 Meeting time:  12:00pm Eastern
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  • Activity updates
  • General discussion


Recording on Zoom: [1]

Participants: B. Moffit, P. King, D. Armstrong, C. Ghosh, H. Liu, M. Gericke, D. McNulty

  • Discussing data rates
    • The links from the MPDs to the VTP are 1Gbps links, so ~5kHz with 6 samples per event should be fine
    • The VTP optical link is 10Gbps Ethernet, so we could handle ~40% occupancy at 5kHz in the GEMs, if we had one VTP
    • When we do zero suppression, the passed data has all six time samples for the channels that are above threshold. The zero suppression is done in the VTP
    • Chandan comments that his simulation using the beam generator in an open sector at 100nA has a rate of about 10MHz (Mollers and elastics); my estimates were based on a Moller rate of 30MHz, so occupancies might be lower than I estimated.
    • David points out that most of our running would not be at the very highest luminosity. Also we can prescale our triggers down to keep the data rate under control.
      • We should not need to use the multiple event builders like SBS is going to need to do in the next running period.
    • David also comments that SBS is getting higher occupancies than they were expecting; this is coming from xrays making single events in individual layers. David has a large beam-generator simulation file from Chandan that should include xrays, so he is planning to try to look at this in simulation soon
    • We'll need to prescale our triggers; as Chandan had said above, the rate per sector is ~10MHz at 100nA, and the maximum event rate we can take is ~5kHz. So we'll need prescales of order 2000.
    • Taking about the FADC window
      • I had estimated data rates based on 38 4-ns samples (152ns). Bryan says that that due to data packaging/transfer issues we might be as efficient using a 256ns window (64 samples).
        • It's best to use 2^m samples in the FADC to take advantage of the bandwidth.
      • With raw mode at 5kHz (and using 38 samples per event), I'd gotten ~850Mbps for the crate with 14 FADC modules; so we should plan on using the VTP readout for the FADCs
      • Also note that we could take most of the events just in pulse parameter mode, and only get the full raw mode periodically.
    • Hanjie asks if the network from the hall to CHA was upgraded to 10Gbps for SBS; Bryan says yes, and they have been able to saturate that link as a test.
      • Probably we can get both the GEM readout and the FADC readout within one 10Gbps link
  • Last meeting Michael had stated the ring-five signals had a 50ns FWHM, but he corrects that they are more like 20-25ns FWHM. But this should still be fine with the 4ns sampling in the FADCs.