GlueX TOF Meeting, November 4, 2014

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GlueX Time-of-Flight Meeting
Tuesday, November 4, 2014
11:00 am EST
JLab: CEBAF Center B101 (non-standard room)


  1. Announcements
  2. TDC Timing Synchronization (all)
  3. Work in the Hall (Aristeidis)
  4. FADC250 readout parameters
  5. Calibration Progress (Sasha)
  6. Responsibility for shift takers' instructions on the hdops wiki (and expert pages too) (all)
  7. Equipment Loan
  8. Final Invoice Paid



Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2014-4Q on the JLab CUE. This directory is accessible from the web at .



  • FSU: Hussein Al Ghoul, Paul Eugenio, Sasha Ostrovidov, Aristeidis Tsaris
  • JLab: Chris Cuevas, William Gu, Mark Ito (chair), Ben Raydo, Sascha Somov

TDC Timing Synchronization

We reviewed the proposal for solving the 24 ns random time shifts first noticed by Aristeidis when comparing TDC and FADC times.

The Problem

With no RF signal available, we want to at least have the TDCs tied to times of the rest of the detector. However, the CAEN TDCs run on a 41.67 MHz clock (24 ns period). This clock is synced to the 250 MHz detector system clock (4 ns period), but the phase of the sync is not currently controlled. Triggers from the detector are always synced to the 4 ns clock. When a trigger arrives, its phase with respect to the 24 ns clock is random and unknown. The "stop" to the TDCs is not issued until the next rising edge of the 24 ns clock following the trigger. This introduces a six-fold ambiguity in the time scale of the TDCs with respect to the rest of detector.

The Solution

There are many actually, but we agreed to implement the one in the proposal, which was worked out by William and Ben.

We still need to implement William's new TS firmware to control the phase of the sync of the 41.67 MHz clock. We also need to check that the TOF's TI is using the 48-bit version of its system clock.

Work in the Hall

Aristeidis told us that there is not much new since the last Bi-Weekly Collaboration Meeting report, other than improvements to the online monitoring histograms.

TOF DAQ Issues

Sasha O. led us through a few topics related to the read-out.

FADC Full Range

He has found that the FADC-250s are set at 1 Volt full-range rather than the 2 Volt setting he has been using at FSU. He finds in cosmic data that 30% of the pulses are hitting the maximum ADC value. Changing the ranges involves moving a jumper on each board and thus removing the boards momentarily from the crate. We agreed we should try to get this done during the upcoming downtime while the tagger electronics are installed in the Tagger Hall.

Counter Ends and TDC Channel Assignments

Sasha has noticed empirically over the last few years that he gets better mean time performance when both ends of counter use the same timing chip in the CAEN TDCs. He proposes for the spring run that the assignment of channels be re-worked to give this configuration for all counters.

FADC Read-Out Parameters

  • Playing with the trigger versions of the number-of-samples-before threshold-crossing (NSB) and number-of-samples-after (NSA) seem to have no effect on the data.
  • Sasha O. showed several plots of the distribution of the pulse integral in Mode 7 with various settings of the read-out NSB and NSA. Sascha S. and he discussed various possible explanations, but we did not settle on a clear explanation for all of the plots.
  • Sasha O. noticed that increasing the trigger threshold for the TOF stand-alone trigger beyond 216 has no effect on the events. He attempted this to try and trigger only on events with multiple TOF counters hit. Sascha S. will check on the number of bits used by the trigger.

Calibration Progress

Sasha O. has run into a couple of problems trying to run through his sample of 7 million events.

  1. He find crashes in the EVIO library for events with a lot of hits.
  2. The code to analyze Mode 7 data crashes for unknown reasons a few hours into the job.

Responsibility for Shift-Takers' Instructions

Sasha O. had already added a lot of detail to the instructions. He will continue to maintain the page.

Mark also noted that there is slot on the Ops Wiki for instructions for TOF experts] which is available if more detailed documentation is needed.