Minutes-10-20-2011

October 20, 2011 FDC meeting

Agenda

1. Production Construction Tracking
   • Status (Dave)
   • First package tests (Lubomir)
   • Resistance of z-axis conductive tape (Lubomir)
2. Engineering (Bill)
   • Cooling/grounding system
   • Other: protective covers, new hubs, ...
3. Electronics update (Chris)
4. Testing set-up at EEL126 (Beni)
5. Other

Minutes

Participants: Eugene, Bill, Tim, Beni, Mark, Vladimir, Chris, Dave, Glen, Simon, Casey, and Lubomir.

Production

- Dave: Working on second package. First end window ready, second will be ready by the end of the day. Two cathodes (type-1) are ready. Another two cathodes (type-2 and 3) just need the daughter cards to be put on (the last operation). The first wire frame was strung and taped, but there were some delays with the position measurements. Wire scanning stops in the middle of the chamber, most likely due to a combination of software and hardware issues. Will try to find the Caleb's original software (Parker ACR project) and use it, at the same time to identify why it stops, which is the signal causing this. Replacing HV caps: we have 4kV caps only for the first two wire frames due to delay in the order, and will have enough at the end of January. Since we can't wait that much will use 3kV caps for the rest of the package.

- Lubomir: Vladimir tested all the channels from cell#4 top cathode to the top of the package. All channels are working. The exception is a noise seen on two channels, one on the bottom cathode and one on the top cathode of cell#6. Some smaller noise is seen also on their neighbors, mots likely induced from them. The noise looks like discharge, a sharp random signals (~10-20ns from the pre-amp) with amplitudes ~100-200mV and frequency ~1kHz depending on the HV. Vladimir checked carefully but couldn't find similar noise on any wire. The top and bottom strip showing noise do not cross each other. The noise appears only if there's HV on sector #4 for the top strip and on sector #2 for the bottom strip. In both cases the beginning of the strips and their traces leading to the connector are very close to the HV distribution chain on the PCBs for the corresponding sector.

- To investigate the noise problem, cell#6 was disassembled. Using a new card (made by Anatoly) now we can measure the resistance between the strip and the corresponding pin on the daughter card. We found that these noisy strips have higher resistance than normal: ~10 Ohms, compared to 1.5~4 Ohms. It was found also that bending the cathode frame may increase the resistance, after some relaxation in may come back, but also may stay higher and eventually can be "fixed" by bending the frame again. Similar problem was found on other channels of these two cathodes. Re-clamping/re-heating the conductive tape solved the problem in all the cases except one, the connector on the bottom cathode that has noisy channel. There Casey had to replace the daughter card. After removing the old card we looked with a microscope: the silver balls from the conductive tape were visible on all the connectors, the conductive tape glue was much ticker between the pads than below the pads (due to the holes between the pads on the flex), no dents on the cathode side, but some silver balls were embedded in the tinned pads on the flex. We discussed possible reasons for enhanced resistivity and decided to do more prototyping with the z-axis conductive tape. Eugene pointed that 10 Ohms is too small to cause noise problems. The strip capacitance was measured after the meeting on a separate cathode (it is very difficult to measure it inside the package since the card used to connect to the strips has much higher capacitance): ~10-20 pF between strips, ~40pF between strips and ground plane. Since in the package we have another ground plane further away one can assume the strip to ground capacitance is <100pF which at 10 Ohms gives a time constant of <1ns to be compared to the 10ns of the pre-amp.

Engineering

- We discussed how to use the cooling tubing as a ground for the pre-amps. Potential problem is when the place of tube separation is bypassed by connections to two cards on one wire board. According to Bill this can be avoided except on the fourth cell where another separation of the metal tubing is needed. To have ground there we may use a fuse (as Mark suggested). Eugene also suggested that if needed we can insulate the tube from the card, but then need to supply additional ground for the card. As it was measured, on the cards between the strips the resistance is ~0.5 Ohms, resulting in a loop current of ~40mA, so don't expect problems there.

- Bill: aluminum protective covers and the new hubs will be ready by 5-8th November. Since we need the covers to start the first package tests at Blue Crab, Eugene suggested to expedite their production.

Electronics

- Chris: according to Cody, we can test "manually" the 22 pre-amp cards needed for the first cell. We need these cards to prototype the cooling loop on one cell and to start the tests in 126.

- Before the meeting Fernando, Bill, and Tim came to an agreement for the color coding of the pre-amps and brackets.

Chamber testing at 126

- Beni: for the tests at 126 will need the translator boards which could be a showstopper; now we have only one. The individual HV cables (that connect to the thick rectangular HV connector) will be installed at Blue Crab.

Other

- FDC section of the TDR: Lubomir will coordinate the contribution of different people to this section: Simon (FDC simulations), Beni (prototype tests), Bill (drawings and related description of the chamber). Lubomir will do the first version of the general description and will coordinate also with Fernando the electronics part. As Eugene explained this should be in NIM-paper style describing the latest state of the detector; requested first draft to be ready within a month.