General Meeting Summary 10/31/19

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)