Minutes 11-19-2007

Special FDC Cooling System Meeting

Date: November 19, 2007

Participants: Daniel, Fernando, Bill

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1). Fernando reviewed thermal measurements that he had made of his

   fully loaded daughter board on the bench.  Both sides of the
   board were in contact with an insulating layer.  Due to strong
   variations in thermal emissivity of the system, he relied on
   measurements using thermistors.  His numbers were as follows:
     > Cooling strap at daughter board end  = 36.4oC
     > ASIC top = 35.8oC
     > +2.5~V regulator = 46.6oC
     > +1.25~V regulator = 39.9oC
     > Copper edging of daughter board = 35.9oC
     > PCB = 35.5oC
   He also measured the temperature along the copper strip that extends
   away from the daughter board.  About 6~in away, the temperature was 
   measured to be 24.3oC.

2). The daughter board card temperatures will ultimately need to

   be kept at a temperature of about 32oC (or about
   90oF).  This is the temperature for which the cooling 
   system needs to be designed.  The basically amounts to a cooling
   power of about 2~W per daughter board (or about 65~mW per ASIC
   channel x 3 chips per board x 8 channels per ASIC).  The good news 
   from Fernando's thermal measurements is that the PCB temperature is 
   essentially the same as the temperature of the copper strip on the 
   edge of the daughter board.  This is due to the good thermal 
   emissivity of the card/ASIC chip heat sink.

3). Bill reviewed his current cooling system design. Each FDC package will

   be fed by a single input cooling line that will wrap around each package 
   in a single loop and then exit the solenoid.  A thin copper or aluminum
   tube will spiral around the package ~24 times (once for each active 
   layer).  The planned size for the tubing will be 4~mm O.D. and 2.5~mm 
   I.D.. The daughter boards cards will each be connected to an L-bracket.  
   This bracket will be in attached to the cooling line via a two-piece
   block (a small aluminum clamp) that connects around the cooling line.

4). Issues in the design:

   - What is the best coolant to employ (nominally we are thinking
     about using fluorinert)?
   - How can the design be made to minimize the material inside
     the solenoid?
   - How best to connect the aluminum cooling blocks to the
     cooling tube?
   - Determine the final heat load that the system needs to
     handle?
   - Can this system be expanded to handle the cooling requirements
     of the CDC and BCAL?

5). Bill stated that when a board is available for testing, he would

   like to have one for his own measurements.

6). Bill will present a preliminary design to the Hall D group in December

   so that folks can give feedback on the design and understand the 
   materials added in the inactive region of the FDC.

Minutes prepared by Daniel. Send any comments or corrections along.