General Meeting Summary 4/16/20

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PARTICIPANTS: V. Berdnikov, A. Camsonne, C. Munoz-Camacho, R. Ent, M. Fowler, T. Horn, C. Hyde, S. Lassiter, P. Medeiros, H. Mkrtchyan, J. Murphy, J. Roche, V. Tadevosyan, B. Wojtsekhowski

MAGNET AND DESIGN (Charles, Paulo, Steven, Mike)

  • Analysis of magnet fringe field data and comparison to calculation is ongoing
  • The Hall A/C engineering/design team is working on NPS cable layout
  • Two main routing options, one more direct but also makes cables longer - seems fine from NPS point of view, but need to check with Hall C
  • Also need to take into account CPS in overall cable layout

* Action items:

  • Send updated DVCS kinematics table with settings moved to Hall C from Hall A to Steven L.
  • Check with Brad S. on cable routing, patch panel, etc.
  • Include CPS in overall cable layout

FRAME (Carlos)

  • Construction started, but on hold until end of lockdown - currently expect re-opening after May 11
  • Crystals and LED connectors arrived in Orsay
  • Cabling of LED connectors is ongoing

* Action item: check on cable making effort at JLab

CRYSTALS (Vladimir, Tanja)

  • Had email communication with Crytur. Vendor is working on a proposal for crystal delivery for rest of FY20 and FY21 - expect update after 4/17
  • A few boxes of Crytur crystals that arrived last month await to be inspected. Furthermore, the expected SICCAS crystal arrived (60 of those to NPS) and await inspection
  • SICCAS crystals were preselected in Shanghai by a FCAL collaborator from Wuhan U. - 13% of all inspected crystals were rejected based on simple visual inspection

* Action items:

  • check on options for Crytur to send ~70-100 crystals to JLab on 30 August. These would arrive in multiple boxes with different invoices due to issues with the carrier on vendor's side.
  • check on options for both vendors to keep producing and sending crystals - options for storage at JLab

HV DIVIDERS (Vladimir, Tanja)

  • Ho San's estimates assuming PMT gain 10^6 and integration time 50ns show anode currents of 13mA (beam current: 11uA) and 80mA (beam current: 50uA) for the most extreme experiment kinematics/configurations
  • three orders of magnitude higher than the 100uA PMT limit
  • would require to reduce gain of PMT by 1000 and rest of amplification done by divider
  • for HV divider might need gain of 25 - regarding increased nonlinearity, note that unlike Primex NPS does not need absolute detection efficiency

* Action items:

  • Check Ho-San's numbers from full-scale calculations with, e.g. CPS framework or direct calculations with photon component only
  • Evaluate how to do physics with possibly reduced PMT gain, e.g. model from G0 experiment


  • Investigation of DVCS with positron compared to electron beam
  • Projections complete, discussions of systematics due to positron beam ongoing
  • Expect to circulate proposal in 3-4 weeks. PAC submission deadline is 1 June.


  • Slides posted - presentation in 4/17 CPS meeting