[Halld-pid] Time-of-Flight Meeting Minutes, September 20, 2016

[Mark Ito]

Folks,

Find the minutes below and at 
https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_September_20,_2016

   -- Mark

______________________________


    GlueX TOF Meeting, September 20, 2016, Minutes

Present:

  * *FSU*: Sasha Ostrovidov
  * *JLab*: Thomas Britton, Brad Cannon, Paul Eugenio, Mark Ito (chair),
    Simon Taylor, Beni Zihlmann


      Announcement

The PMT order for 30 tubes is due in October 27. There is no immediate 
plan to replace tubes; these are spares.


      Review of minutes from the previous meeting

We looked at the minutes from September 6 
<https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_September_6,_2016#Minutes>. 


  * *TDC time windows*. We mentioned last time that these need to be
    tightened up. Beni will tune the parameters once we have beam triggers.
  * *New PMT bases with amplification*. Mark paid a visit to Vladimir
    Popov to to discuss the possibility of using his design for the TOF.
    He was optimistic that it could be done. One concern of ours is the
    AC-coupled output. He says this is an essential feature of the
    design, but he thought that it should not be much of a problem even
    at our rates and that there may be other ameliorations to get around
    it. We need to meet with him to discuss the idea further.


      High Voltage Scan Preparations

Beni had been working with Brad. They are transferring Beni's software 
and Brad is trying to reproduce the voltage settings that Beni finds. 
There are differences of 20 V with a spread of 20 V (Brad - Beni). He 
has also noticed differences in the fit parameters from the fit to gain 
vs. voltage. They are working to understand the differences.

Beni reminded us that we owe the Run Coordinator a one-pager describing 
the program we want to conduct during the run.


      Measuring Difference Rate Between Upstream and Downstream Plane

Sasha has been looking for situations where the upstream plane is hit, 
but there is no corresponding hit in the downstream. He wants to look at 
how much we can reduce rate by putting up some plastic around the 
beamline. He is having a low yield of hits where he gets a four-fold 
coincidence: both ends, ADC and TDC. These are the objects that come out 
of the hit factory. He is exploring how to overcome the lack of statistics.


      Non-Linear Calibration for the CAEN TDCs

Beni has succeeded in measuring the correction curve for the CAEN TDCs 
using a self trigger on the TOF. He can calibrate all channels in a few 
hours. He has not seen perfect reproducibility of the constants; there 
can be variation of a bin or two.

There was a discussion of whether we want to download the corrections to 
the TDCs or whether to turn off the on-board correction and do all 
corrections offline, using the calibration database. We have decided 
that an on-board correction would be much preferable, giving equivalent, 
improved resolution without having to keep track of boards and channels 
as a function of time. Ed is exploring whether this can be done; he 
needs instructions from the factory.

The correction cannot be read back to check it. On the other hand, we 
can re-do the calibration with the corrections loaded and check that the 
resulting spectrum is linear.

Paul pointed out that we should make sure Hall B is aware of this issue.


      NIM Paper

Paul is working on it.



-- 
marki at jlab.org, (757)269-5295

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