User name lkaufman
Log entry time 01:22:03 on June26,2004
Entry number 126897
keyword=PROCEDURE for changing halfwave plate
Procedure for changing the insertable halfwave plate (IHWP):
The IHWP state should be changed approximately every 4 hours of data taking.
1. Tell the Compton polarimeter operator that the IHWP state will be
changing. This way they can stop their current run and start a new
run once it has changed. Try to coordinate IHWP changes with their
runs (so that they get good statistics in each run).
2. HAPPEX DAQ run should also be ended before changing the IHWP state.
3. Call MCC and ask that the halfwave plate be put into the OUT or IN
position (opposite to its current state). If they ask, remind them
that neither Hall B nor Hall C care about the flip because they
don't care about polarization. You can check the status of the
IHWP in the parity controls window which is open on hacsbc2 or the feedback monitor gui which is open on adaql1.
4. Once the IHWP state has been changed, the RHWP state also needs to
For IHWP = IN, RHWP = 6500.
For IHWP = OUT, RHWP = 2250
This can be changed by clicking on the workspace labeled "Parity"
on hacsbc2 and changing the value in the "Laser Polarization &
Parity Controls" gui. The Rotating waveplate should be changed to
the appropriate setpoint. Don't forget to press enter after typing
in the new setpoint. There is a box to the right of the
readback which turns yellow while the RHWP is moving and turns to
gray when it is at the correct setpoint.
5. Pockels cell voltages need to be changed to the correct values for
each IHWP setpoint. This can be done while the RHWP is moving.
This is done in the same gui used to change the RHWP setpoint.
IHWP = IN, Change Gun 3: PC (PITA) POS = 3.931
Gun 3: PC (PITA) NEG = 6.658
IHWP = OUT, Change Gun 3: PC (PITA) POS = 3.665
Gun 3: PC (PITA) NEG = 8.128
Again, don't forget to press enter after typing in each new
6. In the same gui, change the Hall A: IA to 5.00.
7. Start a new HAPPEX DAQ run.
8. In the feedback gui monitor, watch how the Hall A setpoint
changes. If it settles to a value >= 7 V or <= 3 V please page Lisa at 584-5699 or Kent at 584-5852.