GlueX TOF Meeting, October 18, 2016

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GlueX Time-of-Flight Meeting
Tuesday, October 18
11:00 am EDT
JLab: CEBAF Center, Room F326/327

Agenda

  1. Announcements
  2. Review of minutes from the previous meeting
  3. HV Scan Planning
  4. PMT bases with Amplifiers
  5. Re-segmentation of the TOF

Communication

Slides

Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2016 on the JLab CUE. This directory is accessible from the web at https://halldweb.jlab.org/talks/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 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)