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    User name A. Camssonne

    Log entry time 10:52:28 on November 11, 2009

    Entry number 298985

    Followups:

    keyword=Compton - beamline vacuum checks

    http://opweb.acc.jlab.org/CSUEApps/elog02/elog_item.php?elog_id=1497937&PHPSESSID=5d1d3673058b8ef940b7186ada3fa68f

    Entry was made to Hall A to investigate the vacuum at and around the Compton
    Chicane.

    In summary, the vacuum in the Compton Chicane (exit leg) is degrading. It
    looks
    like the Differential Pump station is no longer pumping too well. This is
    because of the poor vacuum at the E-P detector polluting the DP station. Once
    the DP cans are no longer pumping to capacity, vacuum upstream (toward the
    Compton chicane) will degrade.

    Details:

    The pump in question, VIP1P03 shows ~111uA of current via EDM. However at the
    power supply located in Hall A, the current is shown to be 600uA. Not
    good. This
    is a big pump, probably 120 l/sec. Looking up the current to pressure
    conversion, at 600uA the vacuum is ~5x10-7 torr. Not good.

    VCG1P03 locally shows 3x10-8 torr. This is consistent with the EDM
    screen. The
    trip level for this VCG is 6x10-6 torr.

    VIP1H00A&B (the differential pump station ion pumps) are at 4.6x10-6
    torr. Not
    good.

    VCG1H00A (at the EP detector) shows via EDM and locally 7x10-6 torr. Pretty
    typical, but not too good.

    If it is decided that the vacuum must be addressed, it will take ~3 hours to
    reactivate the DP station. Hall A may need to go to Restricted Access to move
    the DP activation box into the Hall.

    G.Greenfield, E.Stitts, S.Suhring, R.Gonzales (via phone).



    A copy of this log entry has been emailed to: folts@jlab.org,xiaochao@jlab.org,yqiang@jlab.org