March 25, 2010 FDC meeting
- Production space update off-site floor plans
- threshold variations in the discriminator section of the pre-amps (Fernando) Fernando's pdf
- PCB status
- Frame modification
- cathode sandwich and wire frame
- ground plane tests (leakage, tension)
- Wire winding update
- IUCF phase 3 contract phase 3 budget
- plans for wire winding upgrades in the summer
- tension specs
- Full scale prototype tests
- Cathode frame redesign
Participants: Lubomir, Eugene, Bill, Daniel, Glenn, Casey, Mark, Beni, Simon, Fernando
Production space update
Two options are being considered: properties behind Office Depot (preferably "Minuteman Press"), and properties around Middle Ground Blvd (at Blue Crab) . The rent price of the latter is half the one at Office Depot, but requires building a room inside the bay area. Our position is that the most promising for FDC construction that needs only minimal modifications is the "Minuteman press". We can share the bay area there with SRF (John Hogan).
- Fernando presented measurements of the discriminator part of the pre-amp cards. The worst card so far is showing ~30% variations (min - max range) in the effective threshold, among the 3x8 channels. The question was whether this is acceptable. We all agreed that we don't want to modify the present design of the cards. The variations of the detector response are expected to be compatible if not bigger than 30%. The only procedure that may be considered if possible, is sorting the ASICs before putting them on the cards.
- Next week the design of the PCBs will be finalized (Fernando, Kim, Dan) and posted on the web. We discussed also the option of having checking points on the sense wire resistors at the readout side, related to the problems with the resistors discussed later.
- The one-piece-g10 frame came back from the shop ready to be glued to the PCB ring, the latter is in the shop.
- Chamber 3 was tested for leakage through the ground plane, using a sniffer at the cathode side gas holes. Once more, the leakage was confirmed. Same test will be performed with chamber 2.
Wire winding update
- Dan informed us about the latest IUCF budget estimate for phase 3 including the wire winding upgrades. This and other topics related to the transfer of responsibilities from Dan will be discussed in a separate meeting on Monday.
- The specifications for the wire tension will be revisited at the next meeting (Lubomir)
Full scale prototype tests
- Several sources of the HV problems we had during the testing were identified:
1. We found inside chamber 1 some metal pieces, like a wire piece, probably from the green cables used for grounding. Bill and Mark discussed how to avoid this.
2. The corona discharge we observed on the PCBs (at the readout side) was obviously causing some of the problems. It turned out that cleaning of the boards with alcohol helped. Probable explanation is that there are impurities in the epoxy (from the wire frame production) which combined with some impurities on the surface of the boards would create the discharge.
3. On one of the boards we found sparking at the card connector. By looking at the pins that were sparking (in dark) we identified the corresponding channels. Replacing two sense wire resistors solved the problem. Possible explanation is that the resistor contacts were damaged when handling the frames.
- After fixing the above problems on chamber 1 we were able to set the HV at 2200V with 60/40 Ar/C02 gas mixture on all sectors.
- Beni informed us about the tests he performed inside the tent with chamber 1. Using a scope he looked channel by channel at the signals (cosmics) from the pre-amps on the wires. He found that about 10% of the channels show high rate signals with amplitudes up to 300mV. These signals would disappear if lowering the HV.
- The plan is to perform such tests for each chamber in the tent as being more efficient, possibly also using DAQ. We also plan to open chamber 1 and try to clean the corresponding wires.
Cathode frame design
- Alex presented his MC results investigating the size of the hole for the beam. Two separate effects have been studied.
1. The first one is the background created by the copper material on the cathodes. No change of the background within the statistics used, was observed when reducing the cathode hole size from the "standard" 2.3, 3.2, 3.9 4.6 cm radius for FDC1, ..., FDC4 to 1.3cm for all the packages. 1.3cm radius is small enough to insure high efficiency for hits with radial distance > 2.3cm as in the standard hole size. The thickness of the copper material (in radiation lengths) is ~20% of the target thickness. This means that the maximum increase of the background (without any hole at the cathodes) will be 20%. So, in principle it is possible to make the hole radius even smaller that 1.3cm.
2. The second effect studied, was the occupancies on the strips related to the size of the sensitive area. The latter is defined by the size of the wire deadening area and fortunately we can make a decision about this size later. Based on the strip rates, Alex suggested 3.0, 3.0, 3.9, 3.9 cm radius for the holes in the wire planes for the FDC1,.., FDC4 packages. The advantage would be that we will have two pairs of equal packages. Further investigations with MC using tracking are needed.
- Bill proposed for the future meetings to have the physics discussions scheduled at the end of the meeting. Lubomir will try to better separate the engineering/organizational topics from the physics ones when scheduling the future meetings.