April 12, 2023, FCAL Insert Installation Meeting

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Meeting Time and Place

Wednesday April 12, 2023 9am At Jefferson Lab, Hall D Counting House and on Zoom



  • Went over the minutes from the last meeting
  • Significant discussion on shims -
    • Malte has a large number of SS straps from the original modules and will serve as the shims to make up for the difference in module orientation of the lead glass blocks
    • Matt Shepherd brought addition SS strap and shim material
    • The original stack up used shims at each step so we should have plenty to reuse if needed
    • Discussed shimming the glass/crystal interface to get good and straight, maybe a sheet all around to give a flat surface for the crystals? Also a conductive rubber pad?
      • Sasha said the conductive rubber pad on the ComCal is coming apart so we would have to find something more robust.
      • Sasha will come up with a stacking sequence for crystals and develop shimming plan for crystals
  • Talked about squeezing one glass module row at a time to ensure we get a proper stack - this can be done and the left plate is loosened to allow the next row
    • If we wish to squeeze the beam right glass modules (1 row at a time) to set up vertical interface with crystals, we can do that with a tool before the crystals (2 rows) are installed
    • The center left cooling plate is being cut into 3 pieces to make it more manageable
  • Malted stated that the existing signal cables will all be removed by today - we can remove chains in the morning
  • We should be ready to pull cables out of dark room next week. Unstacking may start the following week
  • Discussed where rtd's go. 10 total on crystals some near center and edges US and DS flanges
  • Discussed supporting the lead glass module flange above the crystals on the DS end
    • May interfere with cabling the crystal bases
    • Glass modules have housing DS that is smaller than the glass - all load would be put into the first layer joint
    • both glass and crystal modules are designed to be supported by the glass/crystal
    • Glass Module CG is over crystal so it should be ok
    • Cannot support from end of glass module as housing is plastic
  • Sasha updated that cables are on order
  • Sasha stated that he ordered 200 silicon cookies that match original glass module parameters
  • Malte stated that he has spares of the PeeK threaded rods for the glass modules
  • Malte will practice rewrapping of the modules as Matt has brought the fixture and some cut aluminized Mylar
  • Discussion ensued on the Light Monitoring system - stll no decision on the design and method. We will have a separate meeting
    • Time is getting short if we do not wish to hold up the assembly waiting for parts. Need to decide ASAP
  • As found measurements of existing lead glass stack up Media:FCAL_module_stack.pdf
    • The detector was measured from the outside of the aluminum plates that hold in the modules
    • Subtract 18.16mm from beam left to take out plate and shim thickness
    • Subtract 19.69 mm from beam right
    • Subtract 20.19mm from top
    • Subtract 16.13mm from bottom
    • Bottom line, the vertical stack is 1.37 mm higher than the expected value and .62 mm wider over 59 modules
    • Lower half is .66mm more than upper half
    • Beam left is .43mm more than BR
    • This may be due to shims being used. We will see when we take it apart