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September 16, 2010 FDC meeting

Tentative Agenda

  1. Production
    • Clean room update
  2. Electronics: update (Fernando)
  3. Engineering
    • Cathode foil: sole source procurement status (Roger)
    • Wire stringing: status and plans (Bill, David)
  4. Full-scale prototype
  5. Other


Participants: Fernando, Bill, Eugene, David, Mark, Roger, Beni, Simon, and Lubomir.


- The price of the clean room came high after the second bidding (~$300K), but we got green light from our bosses and we hope there will be no other showstoppers. We discussed what we can do in advance without the clean room: Rohacell gluing, Rohacell lamination. We may be able to store the Rohacell rings in the office space of Blue Crab. There's now more space in Blue Crab (the magnet stands are not there) so we may start moving some stuff there (like tables) whenever we have time for that.


- Fernando prepared two pre-amps in discriminator mode, together with the cables and ECL translator. Beni is testing them. Fernando wants us to answer in one week whether they are acceptable. There's some delay with the delivery of the PCBs. They had to be here on Monday, but will have them next week. The contract for the PCB stuffing is ready submitted to the procurement. Will have the first 2x6 PCBs (1st article) within two weeks and after the approval the rest (26x6) will be done in 4 weeks. We discussed how we will store the PCBs: in boxes, wrapped and taped. Fernando is also working on the procurement of the HV mini cables.


- Cathode foils: Roger got an answer from Advanced Circuits that they can't produce the cathode foils because of the big sizes. Roger is still waiting for an independent estimate from them. He submitted to the procurement answers of a second set of questions from them regarding details of the attempts to find another source. Ross Small from the procurement states that "at this point approval of a sole source is not a sure thing" and he suggested advertising it in the FedBizOps site for 21 days. We discussed what are the pros and cons of such advertising. Pros: no longer sole source and it takes only 21 days. Cons: if some vendors decide to bid they have to prove they can do it and go through the same stages (first article production) as with Allflex which will take a lot of time.

- Some of the fixtures for the wire stringing were made in the machine shop. Tomorrow they will drill holes in the granite table in 126, that will be used for stringing. Starting next week Bill will have more time to work on the stringing. David brought the position measurement system from UVA on Friday 08/27. It turned out the motion carriage doesn't have enough travel to cover our chamber (970mm). Last week David disassembled the carriage with the stepper motor and the control from the FNAL wire winding machine and got it working with a very old computer! Bill prefers to have a ready system (stepper motor with the control and the software) that works with the new computers. Beni has a small power stepper motor and we will see if we can use it. Bill wanted to know the status of the tension measurement system at UVA. Lubomir will contact them after the meeting. Bill and Simon prefer to have system like in IUCF: starting vibrations mechanically and optically looking for resonance. Eugen asked about the procedure of repairing the wires if they don't meet the tension specifications. It was already done here by Brian many times.

Full-scale prototype

- Lubomir studied the chamber resolution with Garfield with two gas mixtures (40/60 and 90/10) and simulating also different electronics; see above links to the FDC log book. Apart from the resolutions itself, plotted are also the distributions of the differences, actual minus reconstructed position. Eugene pointed out they are asymmetrical and the uncertainties are big. Simon will use these distributions in the GEANT simulations to investigate the effect on the tracking. When comparing different gas mixtures (page 513 in FDC logbook), one can see that 90/10 has wider range with resolution below 200microns. The improvement for small distances (up to 2mm) comes from the smaller averaged drift velocity with 90/10, while in the 4-5mm region where the field is highly non-uniform the independence of the drift velocity from the field with 90/10 gas mixtures removes the tails in the distributions that we have for the 40/60 mixture. Simulating the discriminator mode (pre-amp in discriminator mode plus high resolution TDC) and the fADC125 without the shaper (that introduces additional integration of 40ns) at the same threshold, gives advantages to the discriminator. If, however, one can reduce the threshold (e.g. by common noise subtraction) from 30mV to 15mV than the fADC is compatible to the discriminator. Simon pointed that without shaper one still has to take into account the cables. Lubomir will update the simulations changing the peaking time from 11ns (pre-amp only) to 14ns (pre-amp plus cable). Still, comparing the resolutions with 11ns and 40ns peaking time the preference is for the smaller peaking time. We discussed whether we can reduce the preamp-cable-fADC125 peaking time to 14ns (question for Gerard) and whether it has to be coordinated with the CDC people. Fernando explained there will be two versions of the fADC125: for FDC and for CDC. The reason is the difference in the dynamic range and the gain of the preamps. Eugene and other advocated to have the same fADC125 for the two detectors.

- Beni is working on the top and middle chamber with the new discriminator card and an analog card connected to the wires. He observes oscillations when the cards are connected to the central wires. Fernando will look at the problem tomorrow. Now Beni is doing tests with the last 24 wires. The reason for the lost Ar bottles is the regulator which at higher temperatures (when there's direct sunlight on the bottle) opens a relive valve. The regulator was replaced but we don't have more spares.