FDC Weekly Meeting
Date: November 5, 2009
Participants: Daniel, Mark S., Beni, Bill, Casey, Simon, Fernando, Mark I., Eugene, Glenn
Next Meeting: November 12, 2009 @ 1:30 a.m.
General Construction Updates
- Fernando provided one of his new preamp boards and we found that in the 90/10 Ar/C02 mixture we were efficient at dV=1800V instead of the 2000V we had been expecting. We saw beautiful signals with very good signal to noise background! We also used the anode board to look at cathode signals and, even though the gain is 5x smaller than the final cathode preamp boards, we saw lovely signals as well from the cathodes. News most awesome! See the FDC webpage for some lovely pictures. - We moved to a 40/60 Ar/CO2 mixture (the nominal gas mixture) and were expecting to be efficient at dV=3000V. We could not get the chamber above dV=2500V without large current draw but we saw no signals. The spacer ring was found not to provide an adequate gas seal. We improved things a bit and were final able to see good signals at dV=2500V with reasonably low current. We were plagued by high oxygen content in the chamber gas. - Fernando now has ready a cathode preamp board (with the new GAS-II ASICS) and we have a test program in place on the single layer prototype, but we are working to improve the gas seal. We expect to be able to turn things over to Fernando tomorrow afternoon for him to begin his battery of tests. - Bill has been working with the gang to improve the spacer gas seal. One problem is that the spacer goes across traces that stick up about 3 mils! He is working to overcome the problem and give us a robust and reliable gas seal. Another issue is that the gaps between the wire frame circuit boards were not fully filled in, introducing leaks under the gas spacer ring. He also found leaks about the rigid-flex assemblies on the cathode frame that was laminated to the wire frame. - Once the gas seal issues are properly and satisfactorily dealt with, we will fill the chamber with the nominal gas mixture and Fernando will need several days to study the chamber response with the preamp boards. When he is done, we will return to stack construction (and maybe leak reduction). - The preliminary FDC stack assembly document draft is located at: /u/group/halld/Engineering/PRELIMINARY DOCUMENTS. The document will be fleshed out during the assembly procedure for the full-scale prototype. - The fact that we seem to be efficient at dV values below expectations from the small-scale prototype (same gas and same cell size) has led us to speculate that the wire size must be different in the two chambers, and most likely it is the sense wire. The full-scale chamber planes were strung with 20 micron diameter sense wire and 80 micron diameter field wire. If the small-scale prototype were strung with 25 or 30 micron diameter sense wire, this would explain the dV discrepancies. We are looking into measurements of wire samples from the small-scale prototype. - The full production wire order for the FDC and CDC has arrived and we are moving to get the SEM work completed to qualify the wire. More to come. Mark will take the lead in contacting the W&M SEM folks to set up the work. - We will have to add steps in our construction plans for leak checking.
Wire Frame Update
- Wire frame P4 has undergone a preliminary electrical QA check and has a few problems that need to be addressed with the connectors and 2 capacitors need to be replaced. We then need to pot the regions that led to HV breakdown problems on frame P1. Wire frame P3 will then follow. - We need to have a dedicated meeting to design what the schedule for work on the Phase 3 wire winding will be. The highest priority for work scheduling will be doing work on upgrades of the wire winding facility. This includes a better strongback design, the design and construction of precision combs, modification to the wire winding table, and a list of other items with the system. Stay tuned, more to come. - The wire frame construction document is located at: /u/group/halld/Engineering/PRELIMINARY DOCUMENTS. We will include the information on the wire electroplating process shortly. - The parts of the jig to use for the wire electroplating operation are in our hands. They will be assembled as we find time. - We need to prepare a document for the electrical QA of the preamp connectors on the wire boards. - DSC, Bill, and Fernando will plan a meeting to go over the circuit board design work for Kim. - Peter Monaghan gave us some contacts for a board house that can make large scale boards and a potential supplier. DSC will give Kim the contact information and let her find out if there is any hope of getting larger size boards.
- Progress updates: * Fernando has delivered the new batch of rigid-flex assemblies after all soldering work was completed. These boards need to undergo a battery of electrical QA checks. * Casey has been working on soldering rigid-flex assemblies to the second of our two cathode sandwiches. Soldering work on the first sandwich has been completed and electrical QA checks are in progress. * Even though we are nearly done with the soldering of the rigid-flex assemblies, we will order another stencil and use it for testing of soldering procedures. - The current draft of the cathode construction document is located at: /u/group/halld/Engineering/PRELIMINARY DOCUMENTS. - We need to prepare a document for QA/stuffing/cleaning for the cathode boards and a similar document for the cathode daughter boards and ground boards.
- An order for more ASIC chips is expected very shortly. Fernando expects that we will have ~40 boards ready by the end of November.
- Bill raised an intriguing idea for simplified the rigid-flex and cathode design. We agreed it might be something that will simplify the design, reduce costs, and make the soldering work easier. As there were some issue to hash out, we decided to take this offline and continue the discussions. The basic idea Bill had was to fold the cathode board through the slot on the frame and to solder the flex assembly to it on the back side. This would eliminate cutting pockets into the back of the wire frame and allow us to increase the trace spacing on the cathode for soldering to the rigid-flex assembly. More to come.
Cosmic Ray Test Stand
- Several meetings ago we focussed on the wiggles seen in the reconstructed wire position from the cathodes (see log entry 419) in the FDC logbook. We believe that the periodicity seen is due to the algorithm Beni is using to determine the U and V centroids. Beni has not gotten back to study this. Stay tuned.
- The FDC short-term work list has been posted on the FDC web site. This is continually being updated and DSC welcomes any feedback or comments from the group.
Minutes prepared by Daniel. Send any comments or corrections along.