General Meeting Summary 5/12/16

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  • Discussion about frame outside dimensions with goal of general facility in mind - design for smallest possible NPS angles at different distances to the front face of the detector, e.g., 5.5, 7.9, and 10 degrees at distances 6, 4, and 3 meters
  • Results for small angle setup:
  • Interference with beamline at NPS angle 5.5 deg at 4 m and no easy solution.
  • NPS angle 6.5 deg at 4 m fits easily, but very difficult to reach 6 degrees. Note that the minimum angle accessible with the sweeper magnet gap when the magnet is placed at a 5.5 central angle is already well within the matrix of crystals. However, it is desirable to have at least one column outside this scattering limit to catch showers.
  • Question: can one settle on 6.5 minimum angle for the detector at 4 m from the target?
  • Results for large angle setup:
  • For detector at 14.5 degree NPS angle and distance 5 meters a support post would need to be relocated, but this may be difficult
  • "Blue-line solution" on slide 9 (see agenda for slides) would work
  • Rails
  • G0 rails not available anymore
  • SOS detector slides (12x 2.43 m long), HES and HKS rails (each about 5 meters long) could be an alternative. The latter are more sturdy
  • WACS NPS positioning: Jixie/Donal have a picture showing NPS in place that they could add for info


  • Discussion about compensation solutions at back of magnet - total field integral is about 4 kG/cm mainly from the downstream end
  • field could be compensated by a permanent magnet bolted to the sweep magnet itself - preferable over a field clamp and allows easier access to, e.g., the coil
  • In general, magnet studies have been completed and final design can begin
  • Action item: additional magnetic field shielding study for PMTs: place a box of soft iron around the magnet to see what thickness is needed to neutralize field
  • Action item: check on rails
  • in vertical, the distance to the deck is about 6 inches - may allow to place the assembly on rails


  • Discussion about what is needed to get ~1000 cables for signal from PMTs to fADCs in SHMS and what length would be required. Alex will check on that
  • A number of low-loss, 1/2" diameter, 75 m length may be available


  • Tests on PbWO4 are ongoing at CUA and Orsay
  • An option for extensions beyond the base NPS, which requires high resolution etc. at small angles, may be available BGO crystals from the L3 detector at LEP


  • Discussion about estimation of fringe fields at location of NPS PMTs based on field map Bogdan provided.
  • field is on order 20-50 Gauss and could be shielded with mu metal around PMTs and perhaps some external soft iron shielding (see action item under the magnet section)
  • additional NPS prototype tests could be done for verification of this scheme
  • Action item: estimate effect of polarized target fringe fields
  • send field map to Hamlet
  • initial estimate is order 100 Gauss, but angle not yet taken into account


  • Discussion about latest results from ODU
  • Discussion about checking on Hall D's experience with C-W bases
  • in earlier reviews there had been questions about linearity and rate capability
  • Action item: determine linearity at high rate for C-W bases for NPS
  • check against default base parameters
  • include amplifier in base
  • must have test with amplifier done before September 2016


  • Discussion about division of major project tasks
  • Additional budget discussions will follow after details on, e.g., steel cutting prices (require final design drawings), are available.


  • Cable management update
  • Magnet updates
  • PMT magnetic shielding update
  • Support structure and frame
  • Crytals and PMTs
  • Other...