SVT Ladder weighting exercise

The Silicon Vertex Tracking detector (SVT) in STAR was removed from the STAR setup and a weighting exercise was under-taken.

Measurements made on 2008/03/28

  • There are two kind of ladder / wafers: Long and short ones
  • For a long ladder of 7 wafers: W=309.5 g
  • Comparison and individual measurements
    • A long empty ladder frame
      • Be structure: 31 g
      • Long carbon: 20 g (two of those per ladder)
      • Total support frame long: 71 g
    • A short empty ladder frame
      • Be structure: 25 g
      • Short carbon: 18.5 g (two of those per ladder)
      • Total support frame: 62 g
    • One sensor/wafer: 3 g
      • Seven of those: 21 g
    • ... making a base Weight for a long ladder = 92 g (frames+wafers but no cable, no electronics, no glue and fixture)
  • The cable weight were estimated (but not measured) to be between 60-75 g [accounts for both ends]

Thanks to Bob Soja for the measurements. Bob also mentioned that the Hybrids are fixed using Epoxy containing Aluminum and stresses that due to the bending of the elements on ladder (curved to the middle), the epoxy could contribute to material and a non-insignificant manner.

Additional numbers from Phil 2008/04/01:

  • Hybrid circuit fully populated, encapsulated, with wrap around cable = 4.3 g
    • There are two of those per wafer so 8.6 g per wafer
    • For a 7 wafer ladder, this implies an additional 30.1 g per ladder
  • High voltage board
    • Short version of the outer ladders:  6.5 g x 2 per ladders (one at each ends) = 13.0 g total
    • Long version for the inner ladders: 16.0g x 2 per ladders (one at each ends) = 32.0 g total
  • Voltage cabling
    • High voltage cabling: 13.5 g and two ends of the ladder implies 27.0 g per ladder
    • Low voltage / signal cabling: 17.0 g each but 4 per ladder so ~ 68.0 g  (this is close to the by-eye estimate above)
    • Total cables: 95.0 g
  • Estimated water channel circuit boards weight ~ 15 g X 2 / ladder = 30.0 g

 The numbers above and numbers from 2008/03/28 would indicate a new material balance (summary and sanity check) as follow

  • Weight of a long ladder of 7 wafers: W=309.5 g
    • Initial base weight (frame+wafers) = 92.0 g
    • 2 Hybrids per wafer on a seven wafers ladder = 31.1 g
    • Long inner ladder high voltage board = 32.0 g
    • Voltage cabling = 68.0 g + 27.0 g (not sure this was part of the initial weight / TBC)
    • Estimated circuit board for water channels = 30.0 g
    • Total = 280.1 g
  • We still have 29.4 g to go and a confirmation of the 27.0 g cabling was part of the 309.5 g total weight