[BTeam] RF gradient calibration options

[Jay Benesch]

I spoke of a particular option which allows beam to remain on at all 
times.  Mike Tiefenback writes of many other options in
https://jlabdoc.jlab.org/docushare/dsweb/View/Collection-20993
One not so obvious difference: Mike writes of 3 MeV cavities while I 
write of the lem minimum, 3 MV/m or 1.5 MeV.

Among the open questions I ask you to weigh in on:

1. one reference C100 cavity or use full C25 energy lock zone?

2. lower energy linacs with three ~300 MeV cavity groupings to get 
factor of two improvement in dp/p?  I did four groups in NL and 
suggested two in SL because the optics is so much more forgiving if one 
gets up to ~300 MeV by the middle of the NL and doesn't change the front 
end thereafter.  100 microns dx with 6m dispersion is 17 ppm dp/p, which 
seemed adequate to me even for my SL example given enough samples.  I 
also wanted to stay in the measured BdL range for the arc magnets.

3. for cavities which lem sets below 4 MV/m for fault reasons, what 
should be done given the non-linearity in the diode polynomials at low 
GSET Mike shows?  I'd probably ask Ops to redistribute gradient in the 
zone to turn the one under test up to 6-7 MV/m for the test.  Your ideas?

4. cavity under test and beam on/off or the ramps I suggested?

Jay