General Meeting Summary 3/10/16

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  • Discussion about impact of rotation on target polarization
  • field uniformity is required when rotating
  • based on information from magnet manufacturer (Oxford) field is uniform along the bore to 5-6 out of 10,000. This seems reasonable. This uniformity is confirmed by actual measurements by Oxford
  • General conclusion: rotation has no negative impact on polarization, but has several benefits for physics goals


  • Simulations based on analytical calculations, use 0.3T vertical and 0.6 T horizontal field. Assumption for smallest angle is 6.3 degrees based on DVCS/SIDIS configurations.
  • Currently, all backgrounds at small angles come from the target. In reality, a piece of the background will come from the beam line
  • Without considering technical issues a vertical field design seem preferable. However, it seems impossible to make a design at small angles that allows for positioning the coils (see more detail in Magnet section)
  • A horizontal field design is more efficient at small angles and overall seems to do a good job.
  • There are different options one may consider for lowering background on the beam side, e.g., extra shielding for these blocks against direct hits (blocks would still be useful to catch showers)
  • Next steps:
  • more detailed background simulations with Geant4 - main point is to verify the results from the analytic calculations at angle of 6.3 degrees and calorimeter at some location. Vardan is working on it.
  • include beam pipe - expect that background dominated by angular drop off as seen previously. Also, beam line background downstream
  • include polarized target magnet if experiments want to use it with small angles


  • Discussion about challenges with implementing vertical field
  • In this design, coils are in the horizontal plane (beam left-right) - at small angles have maximum background there, so need the coils there. However, also need the steel there and there is not enough space for both.
  • Conclusion: vertical field at small angles seems impossible to design
  • Discussion about horizontal field implementation
  • No obvious problems with implementing horizontal field configuration
  • Background studies show horizontal field is good enough
  • General conclusion: continue with horizontal field design
  • Coil quotations
  • Double-wound (saddle) coil design is more efficient reducing the field near the beam line, also needs no field clamp, fringe fields reduced by factor ~4
  • Extra cost of double-winding coil is about $20k - Glasgow could contribute this


  • Background simulations with Geant4 (Vardan)
  • Magnet update
  • PMT HV bases update (Charles)
  • Discussion about other NPS action items
  • Other...