Log entry time 11:16:57 on July16,2004

Entry number 128682

I've attempted to reproduce the figures in Joe's ELog about the vertical 
polarization measurement (for longitudinal running) so offsite folks can check 
it out.  I don't know if the halog image grabber grabbed 'em well.  
Joe's entry is htt
p://opweb.acc.jlab.org/CSUEApps/elog02/elog_item.php?elog_id=1224729


So, what's the interpretation?  I haven't talked to Joe in detail, but I 
understand these to be a Wien scan, so that the maximum transverse component is 
seen about Wienangle=90.  This maximizes the vertical and horizontal 
polarizations, and the asymmetry ratio vertical/horizontal is about 1/20. It 
looks like things scale by at least a factor of 3 (probably a factor of 4) 
going to wienangle=15 degrees, which is where we took production data.

So, my estimate for the vertical polarization from the source during production 
running is:
78% total polarization * 1/20 * 1/3 = 1.3%

I believe that this assumes that all vertical is created downstream of the 
wien. Any vertical created upstream of the wien, I think, would be an offset in 
the vertical asymmetry curve in the wien scan (it wouldn't rotate with wien 
angle). It looks like that component is small. 

In principle, it could be possible to create vertical polarization in
the accelerator (spreader/recombiners?).  Joe Grames is confident
that such an effect is small. 

So, less than 1.5% vertical polarization looks like a reasonable estimate to 
me.  Joe will tell me more about this later.