• Main INDEX
  • Monthly INDEX
  • PREV
  • NEXT
    Make New Entry, Make Followup Entry

    User name silwal

    Log entry time 13:41:25 on November 10, 2009

    Entry number 298758

    keyword=photocathode rotated by ~90 degrees in the injector between the end of HAPPEX III and start of PVDIS

    Excerpts from Joe Grames' email:

    The photocathode was rotated about 1 week ago, between the end of
    HAPPEX-III and the start of PVDIS. I removed the photocathode from
    the gun chamber on 11/2 to heat it and following activation on 11/3 put
    it back in the gun chamber. Based upon before/after "QE scans" the
    photocathode appears rotated by approximately 90 degrees. Consequently,
    we are not at the same location on the photocathode - even though we
    are using the same x/y steering lens value now as before the gun work.

    Another point worth knowing is that during the last power outage the
    hardware which provides remote control of the IA waveplates was
    damaged. We didn't think this was a problem for you considering you
    use PITA instead of the IA, but if ever you're interested to change the
    IA slope it cannot be done remotely. We plan to fix during the winter
    shutdown, after PVDIS.


    At the same RHWP setpoit as we had during HAPPEX, 1200, the current PITA
    slope is about 26-30 ppm/V, which is much larger than ~4ppm/V that we had
    during HAPPEX running. The current PITA position difference slopes are
    about 0.017 and 0.025 um/V, compared to about 0.02-2.0 um/V during HAPPEX

    The feedback has been turned on for the past two days, and the charge
    asymmetry is well behaved. The position differences are below 200 um.

    Position differences from run # 13864 (production run from owl 10Nov09)
    bpm4ax Mean -0.125524 +- 0.0980392 Width 18.4912
    bpm4ay Mean -0.138012 +- 0.107152 Width 20.2099
    bpm4bx Mean -0.137445 +- 0.105362 Width 19.8724
    bpm4by Mean -0.15233 +- 0.111537 Width 21.037
    bpm12x Mean 0.0100528 +- 0.0453234 Width 8.54847

    Usually we would prefer to run with orientation that has a small amount
    of analyzing power, which is just big enough to accommodate the charge
    feedback. A lot of analyzing power makes us more sensitive to higher
    order effects, namely position differences and spot size differences.
    Despite the much larger PITA slope (hence the analyzing power) at
    present, the position differences seem to be under control (at least to
    the extent we care about for PVDIS).

    A copy of this log entry has been emailed to: paschke@jlab.org, xiaochao@jlab.org, rom@jlab.org, kkumar@physics.umass.edu