2009.11.13 - Fitting Tilts in CESRv

Gain Errors

How well can we fit BPM tilts in CESRv using Cbar12,22 data? Do the following:

6x6 tracking, damp 40k turns, sample 16,384 turns
skew quads off for now
10mrad (RMS) BPM tilts
Apply a variety of button gains and resolutions
Fit the resulting data in CESRv, and consider the RMS (applied-CESRv fit) tilts.

Plot these RMS tilt differences against the RMS applied gain, for resolutions of 0, 10, and 35 microns.

It appears that in this domain, resolution plays little or no role in determining how well we can fit the BPM tilts.

Residual Coupling

As another test, apply sk_q02w such that there is a residual coupling comparable to how well we are able to correct the coupling in CESR. Then fit the BPM tilts, without correcting Cbar12 first.

RMS (applied - CESRv fit) tilt = 16.9mrad. This is much larger than our theoretical tolerance of 10mrad.

How large of a residual Cbar12 can we get away with and still fit tilts to within 10mrad?

Note that each data point is a single seed in this plot, NOT averaged over ~50 seeds as per usual. Considering this is a "best-case" scenario, with no resolution or gain errors, we would expect the final requirement on coupling correction to put Cbar12 < 0.005.

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