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 predicting the impact of (additional) shielding on overall magnetic field where the PMTs are
- Rough estimate of 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)
- 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