Difference between revisions of "General Meeting Summary 10/31/19"

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::* back of box - adding shielding is difficult due to cables, high voltage, etc. Can add an incomplete shielding coverage on the back
 
::* 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
+
* Discussion of magnetic shielding and predicting the impact on magnetic field where the PMTs are
::* Rough estimate of magnetic shielding needed:  
+
::* Rough estimate of front magnetic shielding needed:  
 
::::* Transverse size of the box is 60cm (30 crystals at 20cm each)
 
::::* 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)
 
::::* 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
 
::* 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
 
::* Based on numerical calculation can also determine if need additional front shielding
::*
 

Revision as of 14:28, 1 November 2019

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