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    User name paschke

    Log entry time 18:37:50 on August 8,2003

    Entry number 109357

    keyword=RHWP in source / new PC voltages

    The rotating wave plate was installed in the source during this down. This means
    that 1) the polarization sign has reversed again (relative to usually considered
    slow reversal tools, such as the Insertable Halfwave Plate) and 2) the charge
    asymmetry was very large, 3000 ppm, which is outside the range of the IA
    feedback system.

    I undid the changes to the Pockels cell voltages that were applied on August 1.
    At that time, without the RHWP, charge asymmetry was about 2500 ppm too high,
    now, charge asymmetry is about -3000 ppm too low, so this return of the
    original Pockels cell voltages should take care of most of the problem.

    Not so, it turns out. The PITA slope has changed quite a lot: from parity
    run 3799, I estimate the PITA slope to be -51 ppm/V. (incidentally, I also
    estimate the IA slope to be approx. -275 ppm/V).

    So the new Pockels cell voltages should be Pos: 7.596, Neg: 7.305. We will use
    these until we have a chance to do a waveplate scan (we should try to lower this
    extreme PITA slope to avoid other creepy effects like instability or large position
    differences). When we do a scan, we should first revert to the original (best
    circular polarization) Pockels cell voltages (7.383, -7.518).

    I didn't get a chance to check this setting yet. I can be paged (or Bryan can look into
    this problem since he's on owl tonight) after the Moller measurement is done and
    few uA beam returns to the hall.

    By the way, conversion for voltage setpoints is 1 setpoint Volt = 400 Pockels cell Volts.