[Halld-pid] Time-of-Flight Meeting Minutes, October 18, 2016

[Mark Ito]

Folks,

Find the minutes below and at 
https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_October_18,_2016#Minutes 
.

   -- Mark

__________


    GlueX TOF Meeting, October 18, 2016, Minutes

Present:

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


      Announcements

The schedule still had beam for Hall D starting on November 9.


      HV Scan Planning

  * Beni pointed out that doing the HV scan is essentially a gain
    balancing exercise.
  * Brad reported that we are ready to execute program, as far as the
    software is concerned.
  * Sasha asked about the criteria for setting the voltages. Beni would
    like to shoot for a 35 mV MIP amplitude when the hit is from the far
    end of the counter and a 10 mV discriminator threshold. We will have
    to try these settings to see if they yield acceptable rate and
    efficiency.
  * Beni asked Sasha if he could do a timing test with his test set-up,
    triggering in the middle of the counter (with the trigger counters)
    and looking at the mean time difference distribution when the high
    voltage is set to obtain a 50 mV amplitude for MIP particles. Sasha
    will give it a try.


      PMT bases with Amplifiers

On Thursday of last week, we met with Vladimir Popov of RadCon. He 
designed the bases for the tagger hodoscope which have an on-board 
amplifier. Present were Brad, Paul, Beni, Eugene, and Mark. We discussed 
several issues and design decisions that need to be made.

  * Should we continue to use a passive splitter to create ADC and
    discriminator signal paths or should we run a second signal cable
    from the PMT base?
  * Should we add an inductor or transformer to the output stage to
    remove a baseline shift due to the intrinsic AC coupling of the
    amplifier?
  * Should we design a new circuit board or modify the existing voltage
    divider circuit, perhaps adding a daughter board?
  * What is the schedule for the upgrade?
  * How many of the PMT bases do we want to replace? All of them? Some
    of them? Which ones?

We will have to put together a specification that answers these 
questions and gives requirements for gain (i. e., current reduction), 
power limits (i. e., HV supply current maximum), and bandwidth (i. e., 
rise time). There are also administrative questions to be answered 
before work can start.


      Status in the Hall

  * The "TOF1" crate had been disassembled to serve as a test bed for an
    FADC250 pedestal setting problem. ADC read-out is unavailable until
    further notice. Hot Check-Out is therefore impossible right now.
  * The integral non-linearity (INL) calibration is underway. Beni sent
    sample data to Bryan Moffit and Ed Jastrzembski but has not heard
    back from them about the format.
  * Beni found the TOF HV would not come on. The power had been
    disconnect, probably when the HV power supply for the Compton
    Calorimeter was being installed.


      Re-Segmentation of the TOF

Paul presented an idea he has been thinking about for reducing TOF rates 
by changing the geometry of the inner counters. See his slides 
<https://halldweb.jlab.org/talks/2016/TOF-Mods.pdf> for sketches of the 
idea. In summary the beam hole is enlarged from a 12 by 12 cm square to 
18 by 18 cm. Also the current half-length paddles are split into two 
half-length and half-width paddles. The enlarged beam hole itself lowers 
the rate and the increased segmentation helps the cause. Paul also 
showed a plot of momentum vs. polar angle for charged particles with TOF 
matches indicating the angular regions subtended by both sizes of the 
beam hole.


      Action Items

 1. Hot Check Out, after TOF1 put back together. (Brad and Beni)
 2. INL calibration. (Beni)


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