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    User name dalton

    Log entry time 09:52:04 on August 25, 2009

    Entry number 285838

    keyword=Beam energy measurement

    The dipole mapper was finally made to work and the field was mapped. To
    complete the arc measurement of beam energy, we would need to tune
    dispersive optics and take harps scans before and after the arc, which
    may take 4 hours. Due to problems with the accelerator and in the hall
    over the last week we will have to forgo this measurement. The
    accelerator has to be raised in energy by ~0.5% and this has been
    scheduled for this morning.

    The arc field measurement is still interesting. Below is a copy of Mike
    Tiefenback's elog entry.


    1482644 Hall A 9th dipole scanner run #968

    24-Aug-2009 21:26 M_Tiefenback ELOG

    After operations was able to bring the MBSY1C dipole back to its
    operating point (MBSY1C.BDL=299044 G), we were able to lock the system
    NMR probe using probe #1. The devide would not lock on field with the
    default automatic locking algorithms. I set the search mode to
    "DAC+/-5%" and used a DAC set point of 2780. The locked field was
    unchanged for DAC set points across the range from 2730 to 2830, and lock
    was lost quickly outside this set point range. I used the midpoint of
    this span (2780) to guide the NMR probe field scan.

    I executed the 9th dipole scanner and saved the result as file #968. The
    fully corrected field integral was reported as 2391.025 Tesla-mm.
    Converting this to a momentum for a beam perfectly matched to the ideal
    bend angle for the Hall A transport line of 34.3 degrees results in an
    uncorrected momentum of 1197.38 MeV/c. The Beam Energy Monitor table
    conversion for the Hall A dipole set point results in 1197.41 MeV/c,
    which appears to be adequately close.

    It appears that the NMR probe is locking to a physically reasonable
    value, in accord with past performance. This dipole set point was tuned
    to agree with the 1st pass beam energy delivered to Hall A in recent days.