RD-2017-11-13

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Kondo (chair); Alexander, Bob, Craig, Elke, Klaus, Marcus, Martin

Kondo mentions that as of last meeting we are planning to write minutes

Somacis ZZ PCB results, continued ... (Bob)

  • Bob presents an update on Somacis zigzag PCB board tests with X-ray scanner, and respective simulation. The plot of centroid mean vs motor position exhibits a pronounced piece-wise linear behavior, as a consequence of too low APV25 gain (used in order to avoid early saturation) and high enough threshold. Kondo asks whether it could be that 2-pad hits are effectively 3-pad ones with the low amplitude pad below threshold. Seemingly the answer is yes. Alexander suggests to always use 3-pad combination (central hit and its two neighbors), which procedure showed remarkable linearity in the Monte-Carlo. Marcus asks why in addition to a jump there is a slope change. Bob replies that this can most likely be attributed to a constant value subtraction.
  • Bob then shows measurement results using Struck ADCs (hybrid PA + shaper; high gain ~7500, relatively low threshold and no saturation). Even that the plot still shows some wobbling there is no piece-wise linear behavior seen. After DNL correction Bob obtains spatial resolution of ~70 microns (remember: 2mm pitch!).
  • Kondo comes up with a remark that one does not have too many options to replace APV25 electronics. Struck is not really representative (costs, etc). Besides this large surface zigzag strips (compared to small pitch readout plane design) mean "higher gain". Alexander objects that collected charge is anyway seen by very few strips only, no matter what their geometric size is. Marcus suggests that 1) one can try to implement more sophisticated zero suppression online (not a universal threshold, but say keep neighbors of all high signal strips), 2) still better than APV25 electronics may become available. Therefore Struck ADC usage simply illustrates the "best case scenario", which one can try to approach by other means. Craig and Marcus discuss vmm3 electronics (seemingly a similar dynamic range; peak sensing ADC and no multi-hit capability, so e.g. of no use for a TPC application; availability issues). Alexander mentions DREAM electronics, which may become available to us via Saclay.
  • Bob has a chance to continue and shows a summary table of new (improved zigzag) board vs the original one, using Struck readout. He observes less 1-pad hits (~5% vs ~30%), better neighboring strip overlap (~82% vs ~69%) and as a consequence ~70 micron vs ~100 micron spatial resolution after the DNL correction.
  • Marcus suggests to try smaller motor steps (50um vs 100um now) in order to carefully investigate the problematic area close to strip spines.
  • The presentation ends with a discussion of 50um collimator width effects, averaging over the 8mm long X-ray gun slit, etc (Craig says the ultimate answer on the board parameters one will obtain with a real beam only, especially since X-ray gun has a finite divergence).
  • Bob says the presented results (shows as a poster at 2017 IEEE NSS/MIC) can either be submitted as a conference record or a TNS paper. Craig suggests to publish a two-page summary and then submit a separate paper.

Progress at UVa (Kondo)

  • Kondo says that the Cr-GEM gain non-uniformity reported last time was caused by geometrically non-uniform induction gap. He was able to apply a temporary fix (see pictures in the attached ppt file), which solved the problem.

Progress at FIT (Marcus)

  • Marcus reports that they are preparing short proceedings for IEEE. Ordered 10" of aluminized kapton to seal the large prototype entrance window. Needs to glue it now and test the chamber for leaks.

AOB

  • Alexander reports on the progress with TTM company (PCB laser etching). They are in touch with the engineer there, are supposed to have a phone call with him next week and ask several questions about the process details, lead time, costs, etc. Will hopefully have more to say in two weeks.
  • Marcus asks about FIT and UVa students, who are supposed to start working on Cr-GEM simulations in EicRoot. Alexander says he contacted both students and they exchanged first bunch of information.
  • Test beam in 2018: the final FTBF schedule will become available in early December.