FDC Weekly Meeting
Date: December 6, 2007
Participants: Fernando, Bill, Roger, Chuck, Mark, Brian, Kim, Simon, Tim
Next Meeting: December 13, 2007 @ 1:30 p.m.
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 copper 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. Fernando indicated that the temperature at the regulator on the preamp cards should be kept below 100 degrees C 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 (wikipedia article) at about 72 degrees F. It is not clear if 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 construction of a prototype composite cathode plane. We are only planning to ship 3 of the 5 wire frames to the wire winding facility (wherever that is).
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 the cathode strip readout is also underway, pending the new connector positions that the cooling design requires. Chuck will provide the information to Roger.
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 connected 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 250 MHz FADC should be ready for Simon's use on or about January 15.
- 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.
- The FDC short-term work list has been posted on the FDC web site (see http://www.jlab.org/Hall-D/detector/fdc/). This is continually being updated and DSC welcomes any feedback or comments from the group.
Minutes prepared by Simon. Send any comments or corrections along.