General Meeting Summary 4/21/16

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  • Discussion about Vardan's updated GEANT4 simulation
  • various corrections have been implemented - fixes issues observed in last meeting, e.g., spikes in energy spectrum and issues with electrons
  • simulation shows that the minimum angle that can detect any particle is 3 degrees. This confirms that some crystals at small angles will not fire - seems ok as these are only intended for catching showers
  • effect of magnet can be seen directly on pages 7ff - the intensity in these spectra has been normalized to 1 uA
  • the total effect of the magnet based on this simulation on the electron flux is a reduction by a factor of 8-10 - there is a position and energy dependence. Comparing this to earlier studies from PAC40 (see page 25, Figs. 22 and 23) the suppression factor is about 5 for electrons. This is good and suggests that the horizontal field magnet is performing well and electron suppression is even better than originally assumed
  • discussion about the total suppression factor of the present (new) simulation compared to the PAC40 (old) simulation. There seems to be a problem with the photon suppression. In particular, the amount of photons seems different in the new and old simulation - the photon ratio is bigger now and so one sees less of an effect.
  • Action Item: Understand why the photon ratio is different now. Perhaps the assumptions for photons are different, e.g., cuts applied?
  • Action Item: Smallest angle crystals - calculate dose rate for these


  • Discussion about updates from Bogdan
  • The original pipe for the Hall C beam line cuts too much from the magnet steel.
  • Suggestion to use a +/-0.75 degree opening for the exit beam line. The magnet per TOSCA design will work well with such an angle
  • vendor identified and obtained a quotation for a conical pipe for the 2-m long section
  • Found a specific design of the vacuum connection between the scattering chamber and that conical pipe. Designer sent a full 3D model of the beam line. Test of the connecting part being planned.


  • Discussion about table of crystal properties on CUA Wiki
  • Note that crystal light yield at CUA is measured with 2" round PMTs and is consistent with measurements made at Giessen within 1 p.e.
  • Action Item: add information on procedure used for each measurement, evaluation of which crystals would pass NPS requirements, comparison to company provided information, and additional information of specific features of crystal spectra, e.g., Mo absorption peak in transmittance spectra


  • Discussion about plans for magnetic shielding studies - need magnetic field estimation at location of PMTs
  • Brief mentioning of plans for frame contributions (IPNO) and other contributions to project (Glasgow). Before deciding on the details need information on pricing of steel cutting, which requires the design drawings - ongoing
  • Compact photon source planning meeting - likely will be scheduled on scale of one month


  • Follow-up background study (Vardan)
  • Magnet updates
  • Other Action Items from list, e.g., magnetic shielding of PMTs, support structure and frame
  • Other...