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    User name R. Michaels

    Log entry time 16:42:53 on July13,2003

    Entry number 103791


    keyword=L-arm Trigger Mods (part I)

    This note pertains to modifications to the L-arm trigger and DAQ
    prior to GDH July run. Since Robert Feuerbach did most work on
    installing the new S2m detector, and knows more details about that,
    I expect a follow-up halog from him.

    Note, we did not touch R-arm setup since May running.

    On L-arm there are now 4 triggers:
    T1 = S1-or
    T2 = (S1-or).AND.(Cherenkov-or)
    T3 = (S1-or).AND.(S2m-or)
    T4 = 2 out of 3 from among S1-or, S2m-or, and Cherenkov-or.

    S1-or and S2m-or are the "OR" of the various paddles after first
    requiring the 2 PMTs of one paddle both fired, i.e. a "paddle firing"
    means the PMTs on both ends fired.

    T3 and T4 are similar to May running. T1,T2 are new and should
    not be confused with T1,T2 from R-arm. They exist in case something
    goes wrong with S2m (e.g. a hole in efficiency).

    If there is a physical overlap within 10 nsec at trigger supervisor, it
    will show up in the datastream as event type 5. There are no trigger
    T5. One should be able to tell which triggers co-existed by looking
    at the trigger latch pattern (a TDC) as explained in online doc's.
    However, we have arranged that T3 arrives well in advance of the
    other triggers, so it makes event type 3. Under normal circumstance
    one would set ps3 low and other ps factors high.

    IMPORTANT: T1 has a lot of after-pulsing. The secondary pulses
    come normally 460 nsec after the first, but also sometimes 1 - 3 micosec
    after. No attempt is made to blank them off. I recommend running with
    very large prescale factor ps1 to avoid erroneous deadtime calculation !!
    The max ps1 is 2^24 - 1 = 16777215. We may even want to unplug T1
    after we are confident S2m works, to avoid wrong deadtime.

    In scalers, page 6 of L-arm xscaler display is the non-helicity gated scaler and
    has T1-T4 from L-arm. The T1,T2 from R-arm was moved to channels
    17 and 18. xscaler was re-labelled and a sign posted. Meanwhile page 9
    of R-arm xscaler shows T1,T2 from R-arm. Simplest rule: Look for your
    trigger rates on the xscaler display corresponding to that spectrometer.

    24 of the 32 channels of S2m were plugged into available scaler channels.
    Obviously we'll need to install more scalers before the next experiment.

    DAQ: The configs are
    LeftUnbuff -- Default config involving all crates. There is a new crate roc4
    which contains an ADC and TDC for S2m.
    pedrunL -- The usual pedestal run config.
    LeftRoc311 -- A "minimal" config that involves only roc3 (fastbus) and
    roc11 (scalers). This avoids roc4 and roc14.

    At the moment I notice 9th and 10th Cherenkov channels are off on L-arm.
    Perhaps someone is working there ?