Meeting 7 September 2017

From Cuawiki
Jump to: navigation, search


ToyCPS2 (Pavel) - Note: tungsten radiator thickness in the model was set at 0.35 cm instead of 0.035 cm

  • Comparison of effect of 10% vs. 1% radiator (1 vs. 0.1 radiation lengths) from Pavel
  • Downstream photons:
  • Downstream neutrons:
  • Compared with the thick radiator run, forward dose rate distributions for photons and neutrons show better focused photon beam, smaller photon dose rates nearby (~10 cm radially from the beam), and much smaller neutron dose rates. Dose rates at the sides and backward are essentially the same. In the photon radial dose distributions the beam density falls down faster with radius, down ~1 order of magnitude at about R=2 mm and ~3 orders of magnitude at about R=5 mm.


  • CPS2 is a more realistic model of the photon source design including the magnet (wedge) to quickly evaluate different options and establish the list of critical performance parameters to be satisfied in the final design
  • CPS2 is implemented in GEANT3 and available on ifarm for testing design solutions and optimize design parameters
  • Discussion about recent Toy Model CPS2 results (Note: in the graphs color coding is: blue=photon, red=electron/positron, black=neutron, green areas=shielding)
  • In all simulations: z=0 is at the center of the CPS, end of CPS is at z=150cm and scores are shown at z~300cm downstream - no polyethylene shielding implemented yet
  • Muons/electrons are scattered in the radiator, hit lower portion of the wedge - first order one can see a shift in z in photon spectrum because of energy loss in the radiator (dE/dx and bremsstrahlung)
  • Prompt radiation simulation with photon beam on NH3 target with radiator, beam current 3 uA, and tungsten shielding suggests:
  • number of neutrons produced in the target is larger than what exits the CPS (note: nomenclature "amplified" means that number of neutrons were multiplied by a decade in order to visualize)
  • photons are absorbed by the green shielding of the CPS, except for those exiting the collimator - at corners see some cascading
  • neutrons suppressed everywhere may allow for optimizing the shielding
  • effect of radiation produced by scraping on target seems negligible and also low energy
  • Dose rates at the sides - simulations with and without target:
  • z>0 denotes radiation coming from target, z<0 that coming from CPS
  • for z<0 see everything <1 rem/hr, which is normal for JLab experiments
  • at z~200cm observe events coming from cascades at CPS edges (delta electrons/shadow at 90 degree)
  • at z~300cm main contribution is from the target for photons
  • Forward dose rates - photon/neutron
  • For photons see 1 krem/hr (with and without target) at distance 10cm - this is the closest distance to CPS the detectors are expected to be located, dose will affect detectors at small angles, but current experiments are at larger angles, calorimeter can typically handle these dose rates
  • For neutrons dose rates are dominated by production in the target (20-25 rem/hr)
  • Backward production dose rates - in shadow of CPS see neutrons at rates of 0.1 rem/hr
  • Energy distributions
  • shadow: energy of photons much larger when coming from target, photons from CPS have low energy - most likely from neutron capture
  • energy distribution in the wedge (dump/magnet) is constant for z=-100 to z=0 (all inside CPS) - done by trapezoidal wedge design, peak is transition to exit slit
  • power deposition density could be made more flat even by more gradual transition (more wedges)
  • overall suggests that may be possible to extend acceptable power deposition
  • Additional optimizations: need to implement raster, make shielding hermetic, copper inserts to reduce energy deposition
  • Discussion of technical support needs for magnet work

  • Next steps - some for 5 October 2017 meeting:
  • Study impact of 10 cm polyethylene
  • Initial magnet concept with materials, e.g. illustration with a cartoon and definition of the materials
  • Consistently calculate radiation and activation doses
  • Prepare a rough outline of a CPS article - what would be needed for it