I analyzed the 3686 lattice presently under study
in the constant-tunes scenario in order to compare
it to the 4170 lattice now in operation. The 3686 lattice
has a design pretzel of 2880. The 4170 design pretzel
was 3300, but we run it, and I analyze it, at 2850.

The positron current dependence plots are shown here:

4170
http://www.lns.cornell.edu/~critten/cesr/injection/notes/14aug06/bunch_1262/

3686
http://www.lns.cornell.edu/~critten/cesr/injection/notes/14aug06/bunch_1369/

The prima facie conclusion from the beta blowup and
B-parameter plots is that the level of optical distortion
reached at 2.8 mA/bunch in the 4170 lattice is reached near
a positron bunch current of about 1.9 mA in the 3686 lattice.

The dynamic aperture plots are shown here:

4170
http://www.lns.cornell.edu/~critten/cesr/injection/notes/14aug06/dynap_1262/

3686
http://www.lns.cornell.edu/~critten/cesr/injection/notes/14aug06/dynap_1369/

These plots tell a complicated story. The dynamic aperture at high
positron current appears to be at least as good in the 3686 lattice
as in the 4170 lattice, both on-energy and for a 3.8 sigma energy
offset. However, with no BBI, i.e. with no positron current,
the on-energy dynamic aperture shows some asymmetric dependence
of the vertical aperture on horizontal offset, perhaps indicating
some contribution other than geometrical. And for a 3.8 sigma
energy offset, the horizontal aperture is very poor. This may
portend difficulty with beam lifetime when injecting with
no countercirculating beam.

-- jim

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James Crittenden                   Tel. (607) 255-9424
Wilson Synchrotron Laboratory      Fax  (607) 255-8062
Cornell University
Ithaca, New York 14853-8001
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