[Bteam] hall A optics measurements today

[Jay Benesch]

Search the elog for benesch and you'll see eleven elogs from 14:35 to 
18:09 looking at the two sets of harp data taken today.

The only changes made today were to MQC2T09 and MQA1C12 to null vertical 
and horizontal dispersion in hall A respectively.  Dispersion from arc 1 
into the A line was minimal - MQB1A11 and MQB1A21 couldn't perfectly 
null linac 2 but on average it's pretty good.  IPM1C04/IPM1C05 were 
under 0.1mm at 3V 30 Hz RF excitation at end of NL.

Although we did a good job nulling both vertical and horizontal 
dispersion at 1C05 the Twiss calculations using IHA1C05 traces with 
MQA1C04 sweep are less than pleasant.  I could not come up with a 
plausible horizontal dispersion that would get the X emittance below 
1e-9m. SLI shows 5e-5 dpp, so I used that.  I therefore took data at 
IHA1H00 scaning MQA1C20.  Only ten quad settings are needed to get 
minima in both planes, half the number at 1C05.  The horizontal 
emittance measured is a third that at 1C05.

I back-propagated the measurements to IPM1C04 and matched at the front 
of the first arc dipole using quads 1C04-1C08.  Quad changes are small 
except 1C08, ~30%.  I put these into Optim and used it to simultaneously 
optimize at the Compton and pivot.  Results are in 1518938 and 1518940.

I see a few possible paths:

a. Compton background can be minimized with steering, so do nothing.

b. download the 1C04-1C08 changes and check on Compton and pivot, taking 
new 1H00 data after the download.  Re-optimize the end of the line using 
the new data.

c. download the special file which changes all non-dispersive quads in 
the Hall A line and see what happens.

Do you have a better path?  Which of mine do you prefer?

Jay