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    User name M jones

    Log entry time 10:25:04 on August 18, 2006

    Entry number 180635

    Followups:

    keyword=FPP efficiency problem

    It was noticed that the efficiency of the FPP chambers had drop to a low
    level. This was indicated by a very low number of hits in the "fpp_nhit"
    spectra. Normally this spectra peaks at about 23 hits but was peaking at
    4 hits. Other spectra ( TDC, Demux, wire maps) looked ok in shape with
    just the number of hits per 10000 triggers lower than usual when compared
    to the "golden" run.

    It seems that the gas mixture for the FPP is the culprit. They
    found ( Rob, Alexandre, Mark Stevens) that the argon gas
    had not switch to a new bottle. Why this effected the FPP and not the VDC
    is a question. But eveything else with the FPP seems fine. The gas flow,
    HV , LV and theshold are ok. I went into the hall and verified the
    gas flow and LV setting by eye.

    I would guess that it would take at least 6 hours for the FPP
    to recover. I have set up extra histograms in the online replay
    to monitor the number of hits per chamber. I suggested to the
    shift crew that they monitor it.

    A copy of this log entry has been emailed to: gilman@jlab.org