FDC meeting minutes

[Simon Taylor <staylor@jlab.org>]

Hi.

I've posted the minutes for the Dec 6 meeting to the wiki:
http://www.jlab.org/Hall-D/software/wiki/index.php/Minutes_12-6-2007

For convenience they are also appended below.  Feel free to send
comments/corrections/complaints to me.

Simon
_______________________________________________

Attending:  Fernando B., Bill C., Roger F., Chuck H., Mark I., Brian K.,
Kim S., Simon T., Tim W.

*Cooling system

Bill presented two solutions for cooling the preamp cards, one involving
straps between the cooling lines and cards and the second a refinement of
the
scheme with the clamps and aluminum tubes he presented last time.  The
"strap" method did not provide sufficient heat transfer.  The temperature
at the cards
in this scheme would be about 159.4 degrees F, significantly higher that
the ~125 degree F ceiling for the ASICs.  Fernando indicated that the
temperature at the regulator on the preamp cards should be kept below 100
degrees F due to problems of reliability at high temperatures, which means
that at the copper brackets this temperature should be less than about 30
degrees C (=86 degrees F).  The "tube" method leads to about 90 degrees F
at the copper bracket, so it is clearly a better solution than the "strap"
method.
Bill was able to position connectors on the cathode boards for the cooling
system to accommodate both the cathode and anode cards without moving any
of the connector positions on the anode boards, which means that Kim does
not have to modify the STB board design.  The coolant we are planning to
use is fluorinert ([http://en.wikipedia.org/wiki/Fluorinert wikipedia
article] at about 72 degrees F.  It is not clear we will need a chiller,
but it might be nice.   The coolant feed will be in the region of the
rails.  The tubes will be attached to the frames at various places.  One
possible place where the design could be improved is the mechanism of heat
transfer from the brackets to the tube: the current idea is to use thermal
epoxy but a few degree improvement may be possible with another choice.
Tim suggested indium.  Since the "tube" design is right on the borderline
of being acceptable for the amount of cooling the cards need, we should
probably
do a test.  Bill has already generated suitable drawings of the brackets.

*Wire frames for winding test

Brian has constructed 4 of the 5 frames (2 with low density Rohacell and 2
with medium density Rohacell).  The 5th should be done by some time next
week,
whereupon the next task is to work on the cathode planes.  We are only
planning to ship 3 of the 5 to whereever we end up doing the winding.

*Cathode readout

Roger is continuing to work on the rigid-flex boards.  The rigid boards
will have to be 2-layer boards; the board dimensions have also changed.
This means
that another round of estimates from vendors will be needed.  The layout
for cathode strip readout is also underway pending the new connector
positions
that the cooling design requires.  Chuck will provide the information to
Roger.

*HVTBs/ STBs

Kim has started working on the traces for routing HV to the wires.  At the
time of the meeting she needed input as to how many wires should be fed
by a single high voltage line.  After the meeting Simon provided the
scheme we will be using, namely a 20-16-12-12-16-20 pattern for sense
wires
and a 20-16-12-12-16-21 pattern for the field wires.   We also discussed
how the high voltage will be supplied to the boards.  We will most likely
use
pigtails soldered to the boards.  There are a couple of possible
connectors that we could use.  Fernando suggested that we fan out from
52-pin Radiall connectors to which the multi-wire cable would be
connnected on both ends.  These connectors are used by CAEN HV supply
boards.

*Status of drawings.

The drawings are in good shape with the exception that Chuck needs to
incorporate Bill's design for the cooling system.  We should expect PDFs
next week.

*Preparations for ASIC/preamp card tests

Fernando provided Simon two fine-pitch cables, low voltage cables, and
preamp cards with adaptor boards.  He is working on a plan regarding what
studies of the ASIC performance we would like to perform with the
prototype.   He also indicated that a 250MHz FADC should be ready for
Simon's use on or about January 15.

*Miscellaneous items

- The cooling design impacts the positions of the gas inlets.  The metal
inserts may need to be bent at some angle as they exit the frames, which
complicates daisy-chaining
the chambers together with tubes connected to T's.  This needs to be
worked out but is unlikely to be a serious problem.

- We need to identify suitable o-ring material that has no conductive
filler, is sufficiently soft, and reasonably radiation hard.  Tim has some
candidate materials in mind.