July 14, 2011 FDC meeting
- Production Construction Tracking (Dave)
- Wire deadening
- Engineering (Bill)
- Flatness problem: package strongback, gusset rings
- Stringing table modifications
- Electronics (Chris)
- HV tests
- Chamber testing at EEL126
- First cell tests with fADC: cathode resolution(Lubomir)
- Tests with external tracking (Beni)
- Other: naming convention
Participants: Bill, Dave, Chris, Elton, Beni, Simon, Glenn, Caleb, and Lubomir.
- Dave (see the construction tracking): Cell#3 is almost ready, just second phase elements has to be put on the wire frame. The cathodes on cell#4 are ready except the flaps on the type-2 cathode. Now the techs are working on the cathodes for cell#5 using the two tensioning tools. We decided to postpone the wire frame production till we make a decision how to solve the HV problem, discussed later.
- Wire deadening: waiting for the chemicals needed. We will use the square lexan plate for tooling, but Bill will order another plate to be used for this procedure. Bill talking to Brian learned that the chemicals have to be neutralized at the end of the procedure and that was not always done before when experimenting on a testing wire frame. We will try the deadening first on several testing frames before using a production one. Dave with Al's help is finishing the micro-controller and also working on a way to bypass the 1M resistors on each wire channel.
- Bill ordered the strong-back for the packages. One option would be to attach it to the package after it is assembled, and the other is just to assemble the package on the top of the strong-back in which case we need several of them. We want to have flatness on the chambers better than 200 microns, but Bill says with the material budget we have it is hardly possible. Measurements on the gusset ring only show deviation from flat up to 150 microns. The biggest deviation correlates with some scratches made in the production and Bill wants to re-enforce that place with epoxied fiber.
- While the stringing table is not used for now, Bill will modify the strong-back to correct for the flatness deviations. Additional holes needed for the frame ejection plate have to be drilled, as well.
- Lubomir and Anatoly did some tests to study the currents through the HV capacitors. At Blue Crab, one wire frame without wires was put in a gas volume (same 40/60 Ar/CO2) and HV was applied on the signal boards between the wire pads (connected with Cu tape) and the ground. The conditioning of this "wireless" chamber turned out to be very similar to the behavior of the second cell and maybe even worse. After almost a week we could reach only ~1.5kV while limiting the current below 1uA for the whole chamber. This indicates that the HV problems we had with cell#2 could be related to the capacitors on the signal boards.
- Fernando and Chris did similar tests with one signal board in 117. Initially the current was huge, few hundred uA at 1kV. Then Fernando suggested to cover the capacitors with humiseal and that helped. Initially the current was also high but on the next day it went down to ~13uA at 2kV for the whole board.
- Beni: these currents are much bigger than on the prototype and we should replace the HV capacitors with better ones and see if this will help. Elton: there were problems with the HV capacitors for the FCAL bases and they had to change them. We discussed how to proceed, certainly we need to know the origin of the currents. These measurements depend on the humidity, but the capacitors on the signal board are covered with humiseal. So, Chris will measure the current on each capacitor and depending on the results will replace those with high current with capacitors rated for higher voltage. We will do similar tests with the frame at Blue Crab: will cover it with humiseal and then, after conditioning, will identify the capacitors with highest current and eventually replace them.
- Lubomir showed results (page 569 FDC logbook) for the strip resolution on cell#1 using fADC: it is below 200 microns and similar to the resolution obtained with the prototype.
- Beni is testing now the cell#1 with external tracking and using discriminator cards with F1TDC and CAEN ADC for the cathodes. His first results about the strip resolution are similar to the above.
- To estimate the wire resolution on the prototype we used the angle reconstructed from the external chamber (even with poor coordinate resolution the base is big enough to have good angular resolution) and also used two wire frames with parallel wires. Simon will work on the code to estimate the resolution when the wires are not parallel to test the whole package.
- We looked again at the FDC naming convention (see link above) that we discussed already a year ago and was used for labeling the PCBs and foils. We agreed on it. Simon will implement it also in the off-line code, where appropriate.