July 1, 2010 FDC meeting
- 727 B.C. status
- wire frame production plans
- plans for wire stringing in 126
- Cathode redesign: finalizing (Roger, Bill)
- Full-scale prototype tests
Participants: Bill, Roger, Mark, Simon, Casey, Bob, and Lubomir
(A relatively short meeting with some of the key players in vacations, still there were some important and useful discussions)
- Bill: the PR for the clean room is awaiting Teresa Danforth's signature (it's a vacation time). Bill placed a PR (that is signed already) for two granite tables with wheels to be delivered directly in 727 B.C. We will need also in total 11 formica tables for the production. Bill looked already to find some surplus tables. We could take one or two from 126. Before purchasing the rest ($500 each) we will look around to find some. On some of the tables we must be able to put 700-800lb.
- Bill placed a PR for the g10 wire frames (30 pieces); the goal is to have them by middle of September. The template for the rochacell rings will be ready next week. The plan is to have two students (working now with Mark) working on the rochacell. Mark asked where to store the rings. Bill prefers to store them on a flat surface, maybe table. We will look to find some space for storage. Lubomir: today we got 6 more feet in EEL 126 from Hall C. After coordinating with Dave Mack, we rearranged their tables. We will use the extra space also for a new rack for the new gas equipment.
- Bill started working on the wire stringing fixtures. We agree that this work has highest priority right now. Bill discussed the way the wires will be pushed down locally, close to the soldering pads. His idea is to use a diffraction plate with grooves: 50 grooves/mm with about 10 microns depth. The grooves will keep the wires at the same spacing while pushing them down.
- Roger prepared the drawings according to the modifications from the last week: increased O.D. with flaps to improve the grounding. Except for few minor modifications (extra flaps in the areas without cards) the design is ready to go, hopefully next week. Roger will send the design to the vendor. We discussed what our requirements will be. Bill suggested to ask for prices: 1) for 60 cathode foils and also 2) if we use the whole material for about 120 foils. We will have 4 foils in the first article and then 4-6 weeks time to check them and start the rest. We discussed how to transport and store the foils. Bill suggested to have them stored in rolls. Mark had suggestions about the material to separate the foils in the rolls.
Full-scale prototype test results
- Lubomir showed a plot: the mean signal vs drift time. One can see that the signal drops with the drift time. Normally this shouldn't happen: the electrons drift and, close to the sense wire, they are multiplied, so that the gain doesn't depend on the drift time. A possible explanation: the electrons while drifting can be attached to electronegative gas molecules. To check this, Garfield simulations were done adding small percentages of oxygen contamination in the gas mixture. The red dots in the plot represent the Garfield results with 0.1% oxygen contamination. The good agreement suggest that probably we have some oxygen in the chamber. Without oxygen, the Garfield simulations show that the signals do not change with the drift time, except for very small drift times.
- We want to measure the oxygen contamination in the full scale prototype to make sure we understand the problem. Then, the plan is to measure the oxygen from the new design mechanical prototype, to be sure there's no oxygen there. If the problem really is in the oxygen contamination, then without it, we can expect to reach the plateau at about 75-100V ( a factor of ~2 in the gain) lower voltage. This will make also the dynamic range of the signals narrower. To test this we can use the new oxygen sensor, but before that we will try with the old one. We have to pump the gas because of the high impedance of the sensors, but the problem is how to regulate the flow through the sensor so that it doesn't disturb the flow through the chamber. We will go with the Beni's scheme, linked above, in which instead of the rotameter in front of the sensor we will use the current mass flow controller. The latter being used now in the gas system will be replaced by our new mass flow controller. The plan is to install the new gas equipment in a separate rack so that it can go altogether eventually to the shed in the hall. Brian Cross gave us a small pump that can be used in the above scheme.
- Beni prepared several plots, linked above, showing the drift time resolution. Two layers were used with the wires parallel. In one case the drift time in the two layers were compared but for tracks within a plane perpendicular to the layers and parallel to the wires. In the second case Beni included one of the layers in the track reconstruction and look at the predicted hit in the other layer. In both cases he got a resolution of about 200 microns which is encouraging.