Log entry time 00:09:36 on July 9,2004

Entry number 128042

We aligned the Pockels cell according to prescription and achieved 
approx. 1.4% DoLP for both IHWP OUT and IN.  

Performed PC translation scans using a pick-off mirror, a QPD, and
the HAPPEX DAQ.  We were somewhat slowed by surprisingly large 
position and intensity jitter in the measurement; it wasn't clear if
the jitter was real on the beam, or just noise on the QPD. (The
QPD was not unreasonably noisy when not seeing beam.)  Regardless, 
we converged reasonably quickly to a point which gave small 
position differences ( <200 nm, which was zero within errors).  
We inserted the IHWP, and were shocked o see a 1.4 um
position difference.  Most of the rest of the time was spent 
dealing with this problem.

The data was consistent with the hypothesis that the surprising
result from the IHWP=IN state represented a problem (related
to laser polarization uniformity) which polluted the translation 
scan conclusions (for the x scan; the y scan results were still 
deemed reliable).  We reverted to the visually-aligned Pockels cell
center in x, which we believe will still give us small steering. 
We should be able to limit polarization effects using the RHWP.

We finished with a few RHWP scans with and without analyzer,
which will inform us about the magnitude of polarization gradients
and sources of analyzing power in the no-analyzer setup.

It is not possible to estimate position differences "on cathode" with 
this configuration, because the pick-off line did not suitably 
model the optical path to the cathode.  We believe that we are in a 
decent situation; we can reasonably hope that the RHWP and PC 
voltages will be sufficient to allow us to manage the
position differences in the electron beam.

Matt Poelker spent most of the day (and evening) in the tunnel with
us supporting our effort, so if you see him, thank him. (And now he
has to steer beam through the injector. Poor guy.)