Difference between revisions of "Minutes-6-3-2010"

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- Beni discussed several plots on the FDC log book (page 468), showing the wire coordinates reconstructed from the cathode strips. Resolution is between 0.7 - 1mm. Some of the strips are missing. Certainly in some of the areas the resolution is better. The most likely explanation is the noise. There's also a systematic curving of the wire position; Simon and Beni have seen this effect before and probably it will disappear after calibrating the electronics.Beni also studied the effect of changing the field HV from -500V to -700V with always 2225V on the sense wires (page 477): the maximum drift time gets smaller, but the tail up to 400-500ns is still there. Lubomir explains the tail coming from the tracks close to the field wires: if there are no ion pairs produced close to the line between the wires where the field is strong enough, the electrons will take a long path along the field lines till they rich the sense wire.
 
- Beni discussed several plots on the FDC log book (page 468), showing the wire coordinates reconstructed from the cathode strips. Resolution is between 0.7 - 1mm. Some of the strips are missing. Certainly in some of the areas the resolution is better. The most likely explanation is the noise. There's also a systematic curving of the wire position; Simon and Beni have seen this effect before and probably it will disappear after calibrating the electronics.Beni also studied the effect of changing the field HV from -500V to -700V with always 2225V on the sense wires (page 477): the maximum drift time gets smaller, but the tail up to 400-500ns is still there. Lubomir explains the tail coming from the tracks close to the field wires: if there are no ion pairs produced close to the line between the wires where the field is strong enough, the electrons will take a long path along the field lines till they rich the sense wire.
  
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- Simon showed new results of his simulations using Garfield and Heed packages (FDC logbook page 466).  
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- Simon showed new results of his simulations using Garfield and Heed packages (FDC logbook page 469). In the first field configuration with high field voltage, the field lines are  mostly in horizontal direction (between the field and sense wires only). The second configuration is similar to the Beni's measurements with -700V on the field wires and the conclusions are the same. Simon is working on correlating the drift times with the track position. He confirms the tails in the drift time spectra are from tracks close to the wires. We will continue discussing the field configurations on the next meeting.  
  
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- There were problems with the gas control system on Tuesday and Wednesday, it tripped almost every our. Eventually Beni got it working but there's no guaranty how long it will survive.  We hope that before that the most important parts of the new gas system will be delivered. There were also gas problems with the middle layer: the metal gauge gas tube was broken. Lubomir fixed it with putty, but then, without the manometer information, it was difficult to get the middle layer bubbling again. Now all the three layers are bubbling.
  
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For the present gas mixture of 40/60 Ar/CO2 and present field configuration (2200V on sense and -500V on field wires) he showed several events with 90Sr source and also with cosmic muons. After convoluting the signals with 11ns time constant, the signals look very similar to those we see with a scope or with the fADC. The drift time spectra are also very similar to the ones obtained with the full-scale prototype. The long tails above 160ns are coming probably from tracks close to the field wire, but Simon will look into that. Eugene suggested to create an ntuple in Garfield so that one can easily correlate different parts of the spectra with the different trajectories.  
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- Lubomir discussed several plots (pages 470-476) showing the resolution along the wires estimated using different information: top and bottom cathodes, top cathodes and wire positions, bottom cathodes and wire positions. The different methods give compatible results of 140-160 microns resolution from a single strip plane. Since two cathode planes will be used to reconstruct the coordinate along the wires, we expect a resolution of as low as 100microns. This is possible because of the common noise subtraction that allows to use the information from 5 adjacent strips. Lubomir outlined that the fADC is a very powerful device in reducing the noise and therefore it is very important to try to implement similar common noise subtraction procedure in the FPGAs. There were discussions whether such procedure is too complex for the FPGAs. Lubomir will prepare descriptions of the procedures used in his analysis and will discuss them before also on the next meeting with Gerard.
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- fADC data analyses were discussed above
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- Beni was able to reconstruct the wire positions from the cathodes (FDC logbook pages 458 to 463) using conventional ADCs. The resolution is 700 microns. The systematics in the wire position reconstruction seen before is visible now as well: the reconstructed position varies with the coordinate along the wire. Beni still needs to do some work in his code related to the coordinate system. Bill was concerned that the testing the prototype took a lot of time and that the same can happen with the testing of chambers during the production. He and other people proposed possible ways to automate the testing and shared experience from other experiments. We will keep on discussing this at the next meetings.
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- Lubomir re-visited the considerations discussed before (GlueX-doc-757-v1) for the field configuration of the FDC. The charge induced on the strips is not affected by the field configuration. The best, from resolution point of view, is to have a configuration where all the field lines from the sense wire are connected to the field wires. This, however, requires to increase significantly the present voltage on the field wires, while the sense wire high voltage can be reduced only slightly to insure maximum efficiency. As Eugene explained, the influence of the field wire voltage on the amplification is much weaker than the sense wire voltage. So, the problem is, based on our previous experience, the chamber will trip at higher field voltage. Still after the chamber cleaning we might be able to work with somewhat higher field voltage.
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== Other ==
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- Fernando: some minor corrections are still needed and Kim will be ready with the PCBs hopefully by tomorrow. Fernando did some simulations for the heating of the fADC125 and confirmed that the heating is not an issue, so we can power the module as long as we want. He explained that some of the positions in the VXS crate, just above the middle of the fans, have reduced air flow. Fernando was concerned that the software for the fADC125 to be used in CODA (first simplified version) is not ready, while that was promised by the DAQ people two weeks ago.
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Revision as of 18:40, 3 June 2010

June 3, 2010 FDC meeting

Tentative Agenda

  1. Production
    • 727 B.C. status
    • production planning
    • new design one-layer prototype: PCB and cathode PRs, wire stringing fixtures
  2. Electronics
    • fADC125 status (Fernando)
    • PCB status (Kim, Fernando)
    • CAEN HV noise investigations (Fernando)
  3. Cathode redesign Bill's changes proposed on the last meeting (Bill, Roger)
  4. Full-scale prototype test results
  5. Other


Minutes

Participants: Eugene, Bill, Fernando, Glenn, Casey, Mark, Beni, Simon, and Lubomir

Production

- Bill informed us that Ron Bartek promised Tim the specifications for the off-site space to be delivered to Rusty Sprouse no later than Friday. There's no full lease of the property yet. Eugene explained us there's a relation between setting up the Blue Crab off-site space and the Hall B one: same people are involved.

- Bill will take care about creating the production flowchart with Fast Track, based on the above document.

- Brian will bring the fixtures for the wire stringing from UVA on Monday (06/07) and put them in 126. Mark will find space to store the equipment in F117 and as long as there's more free space there, Bill is ready to start setting up the wire stringing. We will use the first articles of the PCBs and cathode foils to produce the new design prototype. We discussed whether we can do the same with the wire and cathode frames: submit PRs for all the frames and use the first ones for the prototype. Bill is confident that the new design will work and we can submit PRs for all the frames; Eugene and Lubomir are also in favor of such decision but we will re-visit this on the next meeting.

Electronics

- Fernando informed us that the DAQ group (Bryan Moffit) is working on the drivers for the fADC125 with LINUX CPU. Beni said he would prefer to use the CPU we have now (VXWorks) because if we can have the LINUX one it will be temporary. Eugene suggested buying a LINUX CPU. Beni explained the three CPUs available now are from different companies, the DAQ people are evaluating them and we better wait before buying such a CPU. Fernando will ask Bryan when we may expect the drivers for the VXWorks CPU. By that time we will use the fADC with the Gerard's program.

- the PR for the PCBs were submitted, expect to have the first article in August.

- Fernando investigated the noise coming from the CAEN HV supply. It radiates rather than transmits through the cables. The strips and wires (mainly the long strips) are picking up that noise. Fernando reduced the noise by re-arranging the ground cable connections. Still two of the cards are showing noise. We discussed if we will have the same problems in the hall, i.e. if the detectors will be picking noise from the same CAEN HV crates that will be used for the FDC and CDC. Fernando explained the HV racks will be far from the detectors, but certainly we have to test this.

Cathode redesign

- Not all of the Bill's modifications are implemented: the keep-out circle at 1057mm is not on the print. Fernando said the cathode foil procurement may take longer (because of the sole source) than for the PCBs; this could be a showstopper for the new design prototype and therefore for the production.

Full-scale prototype test results

- Beni discussed several plots on the FDC log book (page 468), showing the wire coordinates reconstructed from the cathode strips. Resolution is between 0.7 - 1mm. Some of the strips are missing. Certainly in some of the areas the resolution is better. The most likely explanation is the noise. There's also a systematic curving of the wire position; Simon and Beni have seen this effect before and probably it will disappear after calibrating the electronics.Beni also studied the effect of changing the field HV from -500V to -700V with always 2225V on the sense wires (page 477): the maximum drift time gets smaller, but the tail up to 400-500ns is still there. Lubomir explains the tail coming from the tracks close to the field wires: if there are no ion pairs produced close to the line between the wires where the field is strong enough, the electrons will take a long path along the field lines till they rich the sense wire.

- Simon showed new results of his simulations using Garfield and Heed packages (FDC logbook page 469). In the first field configuration with high field voltage, the field lines are mostly in horizontal direction (between the field and sense wires only). The second configuration is similar to the Beni's measurements with -700V on the field wires and the conclusions are the same. Simon is working on correlating the drift times with the track position. He confirms the tails in the drift time spectra are from tracks close to the wires. We will continue discussing the field configurations on the next meeting.

- There were problems with the gas control system on Tuesday and Wednesday, it tripped almost every our. Eventually Beni got it working but there's no guaranty how long it will survive. We hope that before that the most important parts of the new gas system will be delivered. There were also gas problems with the middle layer: the metal gauge gas tube was broken. Lubomir fixed it with putty, but then, without the manometer information, it was difficult to get the middle layer bubbling again. Now all the three layers are bubbling.

- Lubomir discussed several plots (pages 470-476) showing the resolution along the wires estimated using different information: top and bottom cathodes, top cathodes and wire positions, bottom cathodes and wire positions. The different methods give compatible results of 140-160 microns resolution from a single strip plane. Since two cathode planes will be used to reconstruct the coordinate along the wires, we expect a resolution of as low as 100microns. This is possible because of the common noise subtraction that allows to use the information from 5 adjacent strips. Lubomir outlined that the fADC is a very powerful device in reducing the noise and therefore it is very important to try to implement similar common noise subtraction procedure in the FPGAs. There were discussions whether such procedure is too complex for the FPGAs. Lubomir will prepare descriptions of the procedures used in his analysis and will discuss them before also on the next meeting with Gerard.

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