Difference between revisions of "Minutes-8-5-2010"

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== Engineering ==
 
== Engineering ==
  
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- Cathode foils: the PR submitted, waiting for signatures. Roger discussed with Allflex people the grounding of the flexes that is done by vias which can be very costly. Different ideas were exchange: to make the flex longer on the sides and fold it, to use double-sided flexes and connect the two sides with conductive glue at the periphery of the flexes. Roger got also important information from Allflex:  
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- Cathode foils: the PR submitted, waiting for signatures. Roger discussed with Allflex people the grounding of the flexes that is done by vias which can be very costly. Different ideas were exchange: to make the flex longer on the sides and fold it, to use double-sided flexes and connect the two sides with conductive glue at the periphery of the flexes. Roger got also important information from Allflex: conductive film that conducts in one direction only (3M company) can be used instead of the cathode soldering. Has to be heated to 400 deg F, but Bill says this should be OK. Bill will ask for samples and we will start playing as soon as we have the first article cathode foils. 
  
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- Wire stringing: Bill had concerns about the precision of the position system at UVA (see pictures attached above). Vladimir explained how the system works and answered Bill's questions. They have measured the resolution to be 25 microns. Vladimir thinks it can be improved (as Bill suggested), but it is good enough for our purposes. Bill was concerned also about the space the system will occupy and that we have to move it around the table. Different options were discussed: moving the table, using two cameras. Bill: if he would start from scratch, he would build different system with better resolution. The plan is to get the system at JLab, check the resolution and then to decide what to do. Vladimir also explained how the tension measurement works: apply sine voltage on an electrode on the top of the chamber and pick up the signal from another electrode on the top of the wire to look for resonance.  
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- The mylar windows of the FDC packages (2 per package) have to be thicker, as Bill requested. We agreed that their thickness can be increased from 1/2 mil to 1 or 2mil which is a small change compared to the target thickness.
  
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- The next step withe the cathode frame prototyping would be to glue the flaps on the back of the frame and then to glue the mylar foil which is now glued to the transfer ring.  
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- Wire stringing: the strongbacks from UVA have arrived. Bill also will order the pieces needed to attach the pin-rails to the granite table.  
  
 
== Full-scale prototype test  ==
 
== Full-scale prototype test  ==
  
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- Lubomir studied with Garfield the drift velocities and the magnetic field effects for different gas mixtures: 90/10, 70/30 and 40/60% Ar/CO2 (see pictures attached). 90/10 is the best from velocity point of view, since it is almost constant with respect to the electric field, while 40/60 exhibits strong dependence. As for the Lorentz angle, it is a factor of two bigger for 90/10 than for 40/60 and hence the deflection of the trajectories due the magnetic field will be bigger. The effect of these two factors on the drift time resolution are demonstrated at page 507 of the FDC logbook: plotted are the drift time spectra for the two gas mixtures with and without magnetic field. The resolutions are better for 90/10 even the increase of the drift time is much bigger for 90/10 compared to 40/60. Simon: we should consider also the shift in the position along the wire. Eugene: we might benefit from bigger shifts when solving left/right ambiguity. There's also the question of stability of operation with less quenching. Beni will switch to 90/10 mixture at the end of the week. Lubomir also studied the effect of the field wire voltage. The best drift time resolution is achieved with the field wires at zero voltage, in which case there are no filed lines between the field wires and the cathode and the field is more cylindrically symmetric which results in better resolution.  
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- Beni connected the new oxygen sensor. The instructions how to read it in case of different gases are posted at the FDC logbook page 511. Indeed, the measurements confirmed that we have oxygen contamination of the order of 0.1% that explains the mean charge vs drift time dependence.  
  
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- Beni is working with the bottom layer: same high efficiency, hasn't studied yet the top/bottom asymmetry we observed for the top and middle layers. Beni si varying now the field voltage and after that he will switch to 90/10 gas mixture.
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- Now we have estimation for the wire resolution, using two chamber layers with parallel wires and external tracking with the IU chambers. Beni showed several plots from the FDC logbook explaining the procedure. The mean resolution is about 200 microns and varies with the distance to the wire. There's a systematic deviation from the expected by the external tracking angle, that can be corrected for, but has to be understood.
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- Beni set up the oxygen measuring system, first using the old oxygen sensor. The readings were controversial and now he is acquiring the parts needed to connect the new oxygen sensor.
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== Other ==
 
== Other ==
  
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At the end Vladimir suggested to use the milling machine system (with 1mil=25 microns accuracy) in the machine shop to check the UVA position measuring system.
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Lubomir will have a talk at a conference (CAARI2010) next week, the contributed paper is linked above; comments and remarks are welcomed. Whether there will be a FDC meeting next week will be decided later next week.-->
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Revision as of 19:30, 5 August 2010

August 5, 2010 FDC meeting

Tentative Agenda

  1. Production
    • 727 B.C. status
    • equipment/materials needed for the production Casey's list
  2. Electronics: update (Fernando) doc1567
  3. Engineering
    • Cathode foil: flex soldering/gluing, procurement status (Roger) [3M conductive film]
    • Mylar window thickness
    • Wire stringing update (Bill)
  4. Full-scale prototype tests [FDC Log Book, pages 509-512]
    • oxygen contamination measurements (Beni)
    • cosmic test update (Beni)
    • wire resolution results
  5. Other


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