General Meeting Summary 10/31/19

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MAGNET

  • ODU mapping tests ongoing


HV DIVIDERS

  • All dividers are assembled at Ohio U!
  • 2/3 of the dividers have been tested
  • Discussion about divider non-linearity and impact on physics
  • Level of non-linearity should be less than calorimeter resolution, e.g. if ~<1% non-linearity, then should not affect resolution
  • Based on prototype beam tests, the bypassed version of the amplifier gives the expected resolution
  • design acceptable since resolution ~1%
  • will have effect on positioning, but an be corrected offline - more important is that the PMT survives (anode current ~<100ua)
  • How well can non-linearity be measured? - if known well enough then an always correct
  • Discussion about three new (reduced gain) divider designs recently made by V. Popov
  • Test with LED - find average current of PMT, need to know anode current of PMT
  • Take same PMT and check different types of dividers, e.g. bypassed vs. reduced gain, any improvements?
  • Action Item: Collect information for all existing dividers
  • resolution
  • non-linearity


FRAME - MAGNETIC SHIELDING STUDY

  • Comparing PMT specs and field map suggests that with shielding the field is 50G (transverse) and ~100G (longitudinal), so a significant effect --> must pay attention to shielding
  • current shielding: 1mm mu metal around PMT
  • consider adding soft iron and perhaps additional mu metal around entire box including crystals
  • Discussion of mechanical aspects of adding shielding around the box
  • distance front plate to PMT is 20.3cm - adding shielding should be fine
  • back of box - adding shielding is difficult due to cables, high voltage, etc. Can add an incomplete shielding coverage on the back
  • Discussion of magnetic shielding and predicting the impact on magnetic field where the PMTs are
  • Rough estimate of front magnetic shielding needed:
  • Transverse size of the box is 60cm (30 crystals at 20cm each)
  • Typical PMT shielding expectation is to extend shielding by 1 radius of the photocathode (here use half of the transverse size of the box)
  • Need to extend front shielding by ~30cm
  • Back shielding
  • may not need full 30cm extension since field smaller
  • can leave top/bottom open for ventilation - a hole of 1cm ever two centimeters giving a fractional opening of 50% should be ok for magnetic shielding. Note that could increase the thickness
  • Once decide where all shielding is located (geometry) can do a numerical calculation
  • Based on numerical calculation can also determine if need additional front shielding - may not be needed as long as have extended shielding, impact on resolution small, since have radiation shielding anyway
  • Shielding around magnet to reduce transverse field is difficult - try to avoid
  • Action Items:
  • Finalize shielding dimensions
  • Numerical calculations of magnetic field with additional shielding


FRAME - AIR CIRCULATION

  • Hycal and NPS prototype used nitrogen purge
  • Dry air could work too to remove moisture. Also note that temperature of NPS will be 18 degC compared to 14 degC of HyCal


SIMULATIONS - SOURCE OF RADIATION IN HALL C

  • Geant4 simulation for source tracking developed
  • includes NPS in Hall C geometry
  • includes magnetic field map, but NOT the one that includes a magnetic beam pipe for shielding and proper propagation to the beam dump
  • Validation: Results show that the major sources of radiation are the target and the next critical radius (here, beam pipe 2)
  • consistent with expectation for any beam calculation - expect ~1/3 of radiation from these sources
  • observation that have a source from top/bottom of pipe consistent with vertical bend magnet
  • What fraction of background radiation is produced in a specific area?
  • Simulate the shielding in front of the calorimeter with a cut of 10 MeV on the calorimeter distribution
  • Should check the Geant4 default cut - likely is ~100keV
  • Analyze the fraction of particles with <10 MeV and >10 MeV
  • if only have 10 MeV particles can shield
  • Results indicate not much reduction in background radiation even with shielding
  • seems counter-intuitive
  • what magnetic field was used? - need to use the one where have shielding around beam pipe 2
  • discussion about Opera plots of magnetic field - even after magnet there is a big spike (large fields), so need additional shielding
  • additional shielding was implemented in form of a magnetic beam pipe
  • Action Items:
  • Include corrected field map
  • Page 4: make 1D histogram to determine where one has to pay attention


CRYSTALS

  • 64 additional Crytur crystals arrived and have been tested - total number: 414
  • Additional 40 crystals from Crytur are on the way


CRYSTAL PUBLICATION

  • Draft will be circulated in week 11/4 for comments


COLLABORATION MEETING: 3 FEBRUARY 2020 AT JLAB

  • Draft agenda will be subject of discussion for next NPS phone meeting
  • So far suggested agenda items - please send additional suggestions for agenda items to hornt@cua.edu
  • Magnet mapping results
  • HV dividers


NEXT MEETING: THURSDAY 21 NOVEMBER AT 9:00AM (ET)