Difference between revisions of "Minutes-9-30-2010"

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quadratic interpolation gives ~25% better resolution than the linear.
 
quadratic interpolation gives ~25% better resolution than the linear.
  
−
- fADC vs discriminator for the wires: Eugene asked if we have decided. According to the simulations the discriminator gives better position resolution for distances  
+
- fADC vs discriminator for the wires: Eugene asked if we have decided. According to the simulations the discriminator gives much better position resolution for distances  
−
smaller than 3-2mm where good timing resolution is needed
+
smaller than 3-2mm where good timing resolution is needed. For distances bigger than 4mm fADC gives ~20% better resolution. Gerard: realistically, one has to use also 1ns timing resolution for the discriminator; Lubomir will implement this in the Garfield simulations. Gerard wanted to have the raw and convoluted signals from the Garfield simulations.
 +
Lubomir will send him the program to generate the signals. Nevertheless, the biggest advantage of the discriminator card is that it is
 +
close to the detector and one can lower the threshold, which will improve the resolution. At the same time, one can use the cathode information from the FADC
 +
to reconstruct the drift time in the regions where it gives better precision.
 +
 
 +
- FDC gas mixture: Eugene asked about the status. As far as the electronics is concerned one should assume 8x10^4 gas gain that we got with 40/60 Ar/CO2 and 2225V/-500V voltage.
 +
Both wire and strip resolutions improve with increasing signal to noise ratio and the signals with 40/60 were sufficiently high to get the design resolution.
 +
The 4-5mm (distance to the wire) region is an exception, where long tails in the drift time distribution significantly deteriorate the resolution.
 +
This is because of the strong drift time vs electric field dependence. The problem can be solved by using 90/10 mixture but then we can't reach the same gas gain
 +
because of the limited quenching properties of CO2.
  
 
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<!--
−
- Gain of the cathode cards: present value of 2.6mV/fC will work for the FDC. To be safe we specify gain range of 2.0 - 3.2. The problem is that in the current pre-amp design, the next possible gain below 2.6 is 0.91. Lower gains might be needed if the cards generate with 2.6mV/fC. The final decision about the gain can can be made after building and testing
 
−
one full package of 6 chambers.
 
  
−
- fADC125 mapping: the 2.6mV/fC card output should map onto 80% of the full scale of the fADC125. Additional decrease of the range down to 60% is acceptable if it is needed
+
== Engineering ==
−
to match the CDC requirements for the fADC125.
+
−
+
−
- Gain for the anode cards: with the present gain of 0.6mV/fC and gas gain of 8x10^4, the wire signals saturate. Since the cards will be used in discriminator mode,
+
−
the saturation doesn't affect the time information that will be recorded with F1TDC. If there are other saturation effects, like increased recovery time, then we need to
+
−
reduce the gain by about a factor of two. Again, this will be problematic with the current version of the card since 0.59mV/fC is the lowest possible gain. Gerard will look into that.
+
  
−
- Other fADC125 requirements: Lubomir investigated the effect of the peaking time on the resolution (page 517). Eugene: very small effect and it is not worth optimizing.
 
−
Gerard expects the resolution with fADC125 to be closer to the one with discriminator and has doubts about this result. For the next meeting, Lubomir will prepare additional plots using other interpolation methods. Gerard: the common noise subtraction is not possible in the FPGA that collects the information from all the channels, because the zero suppression should be done before that in the FPGAs for the individual channels. Lubomir and Gerard will discuss other possibilities for the noise reduction. 
 
−
 
−
 
−
== Engineering ==
 
  
 
- Preparation for wire stringing: the holes in the granite tables are being drilled now and all the initial parts to be attached to the table are ready. David has been working
 
- Preparation for wire stringing: the holes in the granite tables are being drilled now and all the initial parts to be attached to the table are ready. David has been working

Revision as of 19:19, 30 September 2010

September 30, 2010 FDC meeting

Tentative Agenda

  1. Electronics
    • Update (Fernando)
    • Discussions of the FDC electronics (cont.) [FDC requirements]
  2. Engineering (Bill and David)
    • Wire stringing: fixtures, movement system [[1]], [[2]]
    • Discussions of the stringing procedure (cont.)
    • Other
  3. Full-scale prototype
    • tests with different gas mixtures (Beni)
  4. Other


Minutes

Participants: Eugene, Fernando, Bill, David, Chris, Simon, Beni, Glenn, Gerard (on the phone), Roger, Mark, Casey, and Lubomir.

Electronics

- Fernando: the last PCBs were shipped and will have them by Monday and then all will be sent for assembly (the contract is in place already). Chris checked all the boards visually, and three of them for continuity: only minor cosmetic problems. Gerard implemented the auto-load feature on fADC125. Bryan Moffit will put the new firmware on the module so that we can use it for the next tests. Gerard fixed the third fADC125 and soon will have it ready to be sent to CMU. No news concerning the cathode foils.

- Lubomir updated the document about the FDC electronics requirements, linked above, where you can find more details of the discussions listed below.

- Pre-amps in discriminator mode: GlueX-doc-1364 states: "the discriminator has been optimize for operation between 2-5fC and has a range of 20fC". While testing the discriminator cards with the full-scale prototype the lowest possible threshold was 10fC. With more chambers connected and more noise we may need to increase the threshold up to 40-60fC. Fernando: the above numbers correspond to the high gain mode, in case of a low gain these numbers have to be multiply by ~4.

- Quadratic vs linear interpolation in fADC125: if using fADC125 for drift time measurements, the quadratic interpolation gives a little advantage for 40ns peaking time. If comparing the timing from the strips and wires (this helps to separate the real from the fake hits) the fADC resolution is of the order of 1ns. In this case the quadratic interpolation gives ~25% better resolution than the linear.

- fADC vs discriminator for the wires: Eugene asked if we have decided. According to the simulations the discriminator gives much better position resolution for distances smaller than 3-2mm where good timing resolution is needed. For distances bigger than 4mm fADC gives ~20% better resolution. Gerard: realistically, one has to use also 1ns timing resolution for the discriminator; Lubomir will implement this in the Garfield simulations. Gerard wanted to have the raw and convoluted signals from the Garfield simulations. Lubomir will send him the program to generate the signals. Nevertheless, the biggest advantage of the discriminator card is that it is close to the detector and one can lower the threshold, which will improve the resolution. At the same time, one can use the cathode information from the FADC to reconstruct the drift time in the regions where it gives better precision.

- FDC gas mixture: Eugene asked about the status. As far as the electronics is concerned one should assume 8x10^4 gas gain that we got with 40/60 Ar/CO2 and 2225V/-500V voltage. Both wire and strip resolutions improve with increasing signal to noise ratio and the signals with 40/60 were sufficiently high to get the design resolution. The 4-5mm (distance to the wire) region is an exception, where long tails in the drift time distribution significantly deteriorate the resolution. This is because of the strong drift time vs electric field dependence. The problem can be solved by using 90/10 mixture but then we can't reach the same gas gain because of the limited quenching properties of CO2.


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