[Halld-pid] Time-of-Flight Meeting Minutes, November 4, 2014

[Mark M. Ito]

Collaborators,

Please find the minutes below and at

https://halldweb1.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_November_4,_2014#Minutes

   -- Mark
__________________________________________________

GlueX TOF Meeting, November 4, 2014Minutes

Present:

  * *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 
<https://halldweb1.jlab.org/wiki/index.php/Proposal_on_CAEN_TDC_System_Synchronization> 
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 
<https://halldweb1.jlab.org/wiki/index.php/Proposal_on_CAEN_TDC_System_Synchronization>, 
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
    <http://128.186.19.133/%7Eostrov/nsb-nsa/index.html> 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 2^16 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 
<https://hdops.jlab.org/wiki/index.php/Time-of-Flight_System_Shift>. He 
will continue to maintain the page.
Mark also noted that there is slot on the Ops Wiki 
<https://hdops.jlab.org/wiki/index.php/Information_for_Experts> for 
instructions for TOF experts] which is available if more detailed 
documentation is needed.

Retrieved from 
"https://halldweb1.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_November_4,_2014"

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

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