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
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.