Summary notes 4 February 2020

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  • Magnet
  • Yoke
  • Radiation hard coil
  • Inside the magnet: Copper absorber and W-Cu inserts
  • Segmented radiation shield
  • Tungsten powder, perhaps lead
  • Photon beam physics - requires 2mm diameter photon beam to allow for accurate reconstruction of the exclusive process
  • Compact beam dump:
  • shielding - 20 interaction lengths
  • absorb beam power - raster the beam
  • distribute load over target aread - two concepts: rotate target, vertical oscillation magnet


  • Software tools:
  • OPERA - magnet
  • GEANT4 - photon beam profile
  • FLUKA - activation (Note: Fortran based software)
  • Full CPS+target field model has been implemented and background radiation simulations were carried out
  • W powder is most effective for all shielding - for activation in backward direction lead may be preferable
  • Overall radiation level seems comparable to PREX-II (~60 rem/hr at 2m from beamline near exit)
  • Note: < 1 rem/hr is the requirement for people to work
  • CPS studies suggest that this is fulfilled in the backward and target region
  • Forward region is not dominated by CPS, but by the intensity of target/beamline


  • Simulations getting more reliable and validating results against data (nuclear target data, Hall B)
  • Geant4 had bugs in D2 (fixed), still present for He3 and tritium
  • Discussion about possible "freezing" a JLab Geant4 version
  • Discussion about publishing the results from RadCon group


  • Presentation of the general requirements for a CPS in Hall D
  • 60 kW (12 GeV electrons at 5 uA_, 64ns bunch spacing, beam size ~500um (c.f. Hall A/C: ~100uA)
  • Target: Be - distance CPS to Be target is 55 meters
  • Keep similar inner design with main items to optimize:
  • Weight - should be < 100 tons (size and composition)
  • Collimation/exit for beam properties (electron beam raster)
  • radiation level requirements in Hall D can be higher than Hall A/C (there protect the polarized target), so can make the forward piece shorter
  • Note that there is permanent magnet in the beam line that requires moving the CPS from where it was shown
  • Double raster to focus on target - need this raster since travel over long distance and cannot afford up/down movement (must compensate) as in Hall A/C
  • where should the raster be located? - In Hall A/C it is ~2-5 meters from the target
  • Presentation of the To-Do list towards a fully approved proposal


  • Presentation of the theory and work to address PAC report
  • Presentation of simulations to demonstrate the feasibility of the experiment