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 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