BLTWG Meeting 12/14/2009

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  • Time: 11:00 EST
  • Place: EVO and ESNET (with telephone bridge)
  • Connecting: instructions are here
  • Present: Richard J., Jim M., Igor S., Liping G., Alex S., Tim W., David L., Bill C.


  1. Understanding the Primakov beam energy resolution requirements -- discussion
  2. Progress finalizing results for the tagger magnet resolution -- Alex
  3. Status report on diamond radiator fabrication -- Richard
  4. Update on Microscope electronics -- Igor
  5. Other progress reports -- others


Primakov beam energy resolution requirements

  1. Our current physics requirements for beam photon energy resolution are: 60 MeV (0.5% E0) for Spectroscopy, 12 MeV (0.1% E0) for Primakov.
  2. Someone at Jlab seems to have changed the password of the Reviews web site so we cannot access the original presentations to find what was shown.
  3. We reviewed the arguments for the 0.1% E0 for Primakov, and agreed that this is probably not justified when the FCal is used for the measurement.
  4. The dependence of the integrated Primakov rate on beam energy is weak (see figure) -- no strict absolute energy scale knowledge requirement.
  5. Primakov requirement is based on similar considerations as Spectroscopy: match to resolutions in the detector.
  6. Will not change the design (segmentation is driven by rate requirement) but need to have clear statement of physics requirements.
  7. Suggested change: adopt uniform physics requirement of 60 MeV for both physics programs until reason for more strict requirement is shown.

Diamond radiator fabrication update

Status of Microscope Electronics

  • Control board: FPGA firmware debugging is complete!
    • all functionality there. Robust against Ethernet problems (failing links, traffic etc.)
    • inputs/outputs understood, but calibration of DAC may be necessary. Change of its reference voltage may be necessary to remove the systematic shifts present with the current less-than-required supply voltage.
    • yield of good boards is poor for now: only one of the three prototype boards has a functional DAC. One more may be restored. It is suspected that the ball grid array DAC chip was not soldered on (reflow processed?) with the proper temperature profile. The DAC manufacturer specifies tight processing requirements and it is not clear the company populating the boards is aware. We are currently talking to them to establish where the problem lies with that procedure and make sure this is not a problem in the future.
  • Backplane (control/amplifier board interface and signal feed-through)
    • Layout complete and light-sealing details work out. Design sent in
    • Manual assembly (at least for the prototype) is intended to save cost - all components are through-hole.
  • Amplifier board: in the process of population issues of component reel length came up. Longer reels have been purchased and the company (Sierra) is ready to resume board population upon receipt of parts.
  • Low-level software (microscope comm. protocol-aware Ethernet packet communication routines) exists. General, socket-based, Java-based layers nearing completion (will become part of a proper microscope monitoring suite.) Bench testing of these software layers in the next few days.
  • Full system bench-top test expected in the next few weeks, pending receipt of boards (subject to academic schedules.)

Progress toward a new tagger magnetic field map

  • Bill Crahen is working on the ANSYS model for the tagger dipole. He has a model producing numbers, but so far the output is not making sense. He continues to learn how the tools work.