[Halld-pid] Start Counter Meeting Minutes, March 6, 2014

[Mark Ito]

Folks,

Find the minutes below and at

https://halldweb1.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_March_6,_2014#Minutes 
.

   -- Mark
_____________________________________________________________

GlueX Start Counter Meeting, March 6, 2014
Minutes

    Present:
      * FIU: Werner Boeglin, Eric Pooser
      * JLab: Chuck Hutton, Mark Ito (chair), Tim Whitlatch, Beni Zihlmann

    Find a recording of this meeting [26]here.

Review of Minutes from the Previous Meeting

    We reviewed the [27]minutes of the February 6th meeting.
      * The Rohacell for the support structure has come in.
      * A draft of the TDR contribution went out. Mark has some comments
        that he will send to Eric.

Lenzer visit to Eljen

    We discussed the charge to the committee (Bruce, Werner, Eric, Mark)
    and the QA checklist that Bruce has produced.

    We also discussed sending another physicist to Eljen to accompany
    Bruce. Feelings were not strong on this, but we generally thought that
    Bruce would do fine on his own. We noted that there will be a
    conference call with Chuck Hurlbut.

Counter Construction Status

    Eric gave the report.

    Eljen has shipped a single prototype counter to McNeal. The QA guy at
    McNeal reports that the scintillator is nominal and that machining
    should be no problem. There was no report on the physical appearance of
    the scintillator, but this is the same guy who reported the bubbles and
    he didn't say anything on this aspect.

    There have been some minor modifications to the test stand.

    Eric has done a scan of the y-position of the scintillator with respect
    to the SiPM. Results are still being analyzed.

    He has also started work on the Monte Carlo, looking to extract the
    path of charged tracks through the start counter. This information will
    be needed to get the time-walk corrections.

Support structure construction status

    We discussed whether we need to make allowances for wrapping and
    manufacturing tolerances in the mechanical design. We had an ad hoc
    meeting on the same subject on February 7. Chuck, Eric, Mark, and Tim
    were present. If these effects are significant then that will increase
    the radius of the array. For example, if we need to account for 400
    microns of separation between the counters, then the radial position of
    the counters is displaced 2 mm. Since the sensitive area of the SiPMs
    is 3&\times;3 mm, this would need to be accounted for.

    We discussed various of ways of assigning a reasonable tolerance. If
    too much is assigned, then there will be over-large gaps between the
    scintillators; if not enough, the scintillators will not line up with
    the SiPMs.

    Werner pointed out that you could have a lightly greater radius of the
    array at the upstream end where the SiPMs are and a slightly smaller
    radius at the downstream end where the acceptance is more important.
    That takes pressure off of alignment upstream and closes gaps
    downstream. This could be introduced by a very small bend and/or
    shimming.

    Chuck will work on an set of options in the mechanical model. He will
    also look into the feasibility of Rohacell shims. FIU will make some
    additional measurements on prototypes to characterize size variations.

    The support ring and inner Rohacell support have not been machined yet,
    but we have to make a decision soon. We will exchange emails next week
    on this issue.

Electronics Status

    Mark received a report from Fernando Barbosa:

    We will start a final round of tests next week. We are also waiting for
    the aluminum ring to get fit the boards. It would be nice to know when
    as we will need it in two weeks.

Action Items

     1. Send comments on TDR to Eric. -> all
     2. Incorporate tolerances in the mechanical model.
     3. Take additional measurements of the prototype counters at FIU.

    Retrieved from
"https://halldweb1.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_March_6,_2014"

References

   26. 
https://halldweb1.jlab.org/talks/2014-1Q/start_counter_2014-03-06/index.htm
   27. 
https://halldweb1.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_February_6,_2014#Minutes

-- 
Mark M. Ito, Jefferson Lab, marki at jlab.org, (757)269-5295