• Main INDEX
  • Monthly INDEX
  • PREV
  • NEXT

    User name paschke/kaufman

    Log entry time 17:30:39 on January 8,2003

    Entry number 91025

    Followups:

    keyword=IA system re-calibration



    16:20 Around this time, we started our test of the IA system rotating waveplate.

    The current suspect is picomotor S1, which is available through the epics variable
    OPCR00LS2hcurrent_pos
    The other motor suspected is S2, OPCR00LS1hcurrent_pos

    Run IA voltage Picomotor S2 S1 Aq(bcm1) Aq(bcm2)
    1118 5 0 0 484 505
    1119 9 0 0 807 837
    1120 9 -500 0 931 967 ...
    and we lost the beam.

    17:00: IA cell has been set back to 5 V and S2=0.

    Comparing run 1119 and run 1120, it seems that the charge asymmetry is
    different by 130 ppm. With 4 volts on the IA, this would imply that the slope
    has changed by ~30 ppm/Volt, which is consistent with Matt's expectations. Yay!

    The expectation on these picomotors is that 500 pts (1 click in Matt's parlance)
    corresponds to 1-2 degrees on the waveplate angle. Operating angles
    between 0 and 20 degrees correspond to lever arm of 0-400 ppm/Volt, so 1 click
    is expected to be 20 ppm/Volt.

    We have had charge asymmetries as large as 1500 ppm, so for the time being, we need a monster slope on the IA. We should try to create a slope of at least 300 ppm,
    which would mean that we need 8 "clicks", and a readback on S2 of about -4000.

    Beam is gone for a while, and Matt has left for the evening. Instructions have been
    left with MCC on how to continue this test. We should continue this when we
    have beam. The process is as follows:
    1) coordinate with Hall C. They need to monitor their charge asymmetry to verify
    that this is really our motor. (The fear is that what we saw was a freaky fluctuation,
    and S2 isn't actually our picomotor.)
    2) Take a parity DAQ run with IA=5 for a baseline.
    3) Take a parity DAQ run with IA=9 for a second baseline. You should expect Aq to
    change relative to step 2 by ~330 ppm.
    4) Change the setpoint on S2 to -1000. Take a parity DAQ run. You should expect
    the charge asymmetry to change from step 3 by ~240 ppm.
    5) If you see what we expect in step 4, and G0 doesn't see any effect, than we should
    boost our cell a bit more. Ask MCC to move S2 to -4000. We should expect an
    IA slope of about 300 ppm/Volt. We should do an IA scan (IA setpoints at 1, 5
    and 9) to verify this slope.

    If this works, we can start the feedback and see what happens!