June 30, 2011 FDC meeting
- Production (Dave)
- Status Construction Tracking
- Second cell HV tests
- Radioactive source usage at Blue Crab
- Engineering (Bill)
- Package flatness measurements
- FDC cabling
- Other: gusset rings, lifting frame
- Electronics update (Fernando, Chris)
- Chamber testing at EEL126 (Beni, Lubomir)
- First cell status top/bottom asymmetry
- Future plans
Participants: Eugene, Bill, Dave, Chris, Mark, Roger, Simon, Beni, and Lubomir.
- Dave (see the Construction Tracking link above): cell#3: cathode type-2 needs three rigid-flexes (they were glued but Casey found they had solder bridges on the connectors), cathode type-1: the rigid-flexes to be glued. Since Monday we stopped working on the wire frame that was strung, due to possible tension problems discussed later. cell#4: first cathode tensioned, gluing foils for the second one. In addition techs are laminating wire frames, 6 ready so far. Beni asked if we cover the wires while soldering; not yet but we have the cover ready and will try it for the next wire plane. So far we have seen one solder ball on the wires, and Casey removed it.
- Lubomir on second cell HV tests: the cell is assembled as a package, now with lexan sheet on the top. The gas is running since Tuesday evening and since Wednesday we are conditioning the chamber. Today we are at 1800V/-500V with a current of 120-130nA for the whole chamber, which is at least 10 times smaller than the first cell. So, most likely the HV problems we had with the first cell are due to the ultrasonic cleaning in water (nobody was surprised).
- Thanks to Bert Manzlak and RadCon people there's a significant progress with the source usage at Blue Crab. Keith Welch proposed using 25 micro-Curie 55Fe source which is bellow all regulation limits, but according to JLab rules they will most likely require creating RCA at Blue Crab and some additional restriction. Yesterday Bert and Vashek Vylet (RadCon) were at Blue Crab and didn't see any problems for having a source there. Now it's up to Rusty Sprouse to decide and see if there's something in the lease explicitly saying that we can't have a source there.
- Roger: AllFlex has finished the production of the cathdoes, we have now 70 foil sets. They wanted to know what to do with the rest of the material: to keep it there for possible future production or to ship it to us. Almost all the foils were checked and Anatoly found some deviations in 2 of them (possibly can be used). As for our side of the production, two foils were damaged out of 8 cathodes, but that was at the beginning and Bill improved the cutting tool. Eugene: let's keep the material there for couple of months and then decide.
- Based on the results with the first cell (discussed below), it looks like we have some kind of frame deformation and Bill wants to investigate it. The plan is to put the first cell package on a flat surface (like granite table) and measure the deformation of the frame. There were different ideas how to do it, but we expect deviation of 1-2mm which must be easily measured. Maybe related to that Casey noticed that the strong-back was sagging and asked for help people from the survey group. By the end of the meeting we learned the results of their measurements: the strong-back is sagging in the middle by ~2mm. After meeting discussions: we will ask them to do also a survey of the first package in situ at 126 using the same tool.
- On Tuesday there was another engineering meeting about detector cabling. Here, we started talking about the FDC cabling but since it interferes with the other detectors the discussions became more general and conceptual. Also some ideas came out, but not clear at all how realistic they are. Beni: CDC and FDC must be in one skeleton together with the cables. Bill developed further that idea showing also how the cables would run out of the detectors. As Eugene mentioned yesterday on the collaboration meeting, just to change one pre-amp card on the FDC it will be a major operation. Lubomir: what if we pre-install the four (or less) spare chambers in the four packages (making them packages of 7 chambers) connect them with cables that will not be connected at the electronics side and use them if needed. Bill says from construction point of view these are minor changes, there might be problems running 4x22 additional signal cables and also this is additional material.
- Caleb reported on the wire position measurements using the new software and the new encoder. Even his results are not final, they make sense.
- Chris: 165 CDC cables are tested and 80 FDC type-1 cables arrived, not tested yet.
- According to Chris the three rigid-flexes with solder bridges on the connectors can be easily fixed. For the future Chris will test the incoming rigid-flexes just for connections to ground (easy with the testing board) and fix the connectors if needed. The other option would be to send the rigid-flexes back for repair, but we decided not to do this.
- On the first cell so far we can use one HV sector, the other three trip at voltages above 1200-1300V. Now we have 1550V/-200V with 90/10 Ar/CO2 and we have gains high enough to do tests, although the current is too high, ~500nA, but stable. By blowing nitrogen on the HV board capacitors that are outside, the current dropped significantly, indicating that a good fraction of the current comes from there.
- We found again, in the middle of the chamber, top/bottom cathode asymmetry (FDC notebook, page 568) as with the prototype; this time the signals from the bottom cathodes are higher by a factor of 2. By turning the chamber vertical (and using source there) and then upside-down we found the effect goes with the gravity. It indicates again that we are dealing with some frame deformation. We discussed if it could be sagging of the wires or foils due to lost tension, but most likely as Eugene suggested, it can be explained only with the frame having a potato chip shape. According to Eugene's explanation even if the wires are running straight (no sagging) the middle of the cathodes will go up by a half the size of the deformation on the sides. Since we see ~2mm effect in the data we expect to find also frame deformations to be about the same.
- To investigate this, in addition to the frame survey, we plan to place the chamber outside on a flat table and do the same test using source. By lifting the chamber resting the brackets, we can study the effects of the frame deformation.