Meeting 1/27/22 - COMTRA

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  • Joe reviewed schedule again, beam test window is shorter at UITF, now from Jun 1 - Oct 31, see slide 4 media:220127_COMTRA.pptx

ME layout

  • Joe proposed moving polarimeter test to non-dispersive "straight" section to avoid any energy dependent position jitter
  • Shaun showed UITF beam line, identified how we could remove single spool in 4' pass-through, leaving irradiation line intact
  • Joe is confirming this with Matt as first priority location
  • Riad showed model/pics of ceramic break & radiator we'd like to use, 6mm thick copper, 1" flat surface for beam, approved for 10 MeV/100uA with cooling
  • Riad will discuss with Eric if 6mm okay - then we move to fabricate second ceramic break & radiator

DAQ Procurement List - Chris and Riad

  • List of components needed to build two portable DAQ systems: media:ComptonTransPol_DAQ_PurchaseNeeds_2022Jan.xlsx
  • Discussed possibility of running local EPICS, to provide convenient controls to DAC, PS, Helicity Board....Riad will discuss/confirm path forward

Polarized Target

  • Lakshmi will review the overall plan, when ready small group will meet to begin reviewing her questions about function and requirements


  • Greg has installed Geant4 and loaded files to run some of the examples
  • Greg would next like to learn to run and interpret output from the model Ben & Eric developed, then can add the radiator we'll use

Detector update - Eric

  • I am in contact with the Alpha-Spectra company which was providing BGO crystals for a local project we had in Orsay. This is a US company which provides crystals with a guaranteed 8-9% resolution. At the time we were investigating for an order they were less expensive than Saint-Gobain and turned-out to be more performant (we performed dedicated measurements to test this).
  • They should be back to me shortly with information about availability of improved radiation hardness crystals as well as radiation limits of the crystals they are currently providing.
  • It should be noted that litterature about radiation aging of BGO crystals indicates that after a rapid loss of about 20% of transmission, the performance is kind of stable. Some experiments chose to first irradiate crystals to operate in that regime.
  • We may need tools to control the overall stability of the experimental signal... dedicated cosmic ray calibration run or light illumination... too early stage to provide a direction of answer, but this should be kept in mind.