I have done the BBI calculations of electron lattice function
distortions vs positron bunch current for the new 4160
lattice design 4160_2ma_113005, which includes compensation
for parasitic crossings of strength 2 mA as described here:
http://www.lns.cornell.edu/~dlr/cesrc/bmad_4160_111005.html

I compared it to the design which was not compensated
for the parasitic crossings 4160_111005 and found
agreement with DLR's conclusion that the compensated lattice
extends the current limit by about 1 ma/bunch relative to
the uncompensated lattice.

However, I also compared these lattices to the operational
lattice of September at 4260, and found the new
uncompensated 4160 lattice to be much worse than
the old (uncompensated) 4260 lattice. The new compensated
4160 lattice IS better than the old 4260 lattice, but
perhaps not as dramatically as a whole mA.

The comparison of the 4260 lattice and the new compensated
4160 lattice is shown here:
http://www.lns.cornell.edu/~critten/cesr/injection/notes/6dec05/all/

The comparison shows the positron bunch current dependence of maximum horizontal beta and
Welch-Temnykh B parameter.

These calculations were performed in the 8x5 configuration employed in September, 2005 at 4260 MeV.
The effect of the beam-beam interaction at the IP has been excluded.

The first two plots (old 4260:left, new 4160:right) show the increase with positron bunch current of
the maximum value of the electron horizontal beta function in the ring, which is MUCH smaller in the
new 4160 lattice. The value reached at the empirical operating limit of 2 mA in the 4260 lattice is
not reached until a bunch current of 4 mA in the new lattice. It is also interesting to note that
bunch 1 suffers more in the new lattice,while bunch 3 is better off. The new lattice design was
optimized for bunch 3 rather than bunch 1.

The second pair of plots show the increase with positron bunch current in the Welch-Temnykh
parameter normalized to bunch current.The limiting hyperbola of B = 1.2 is included, showing the
value of bunch current where the lifetime is expected to go bad. The improvement in the new
lattice is still appreciable, but not as dramatic as for the horizontal beta function. Here bunch 1
is the worst case in both designs. The limiting value for t1.b1 is 2.4 mA in the old lattice and 2.8
mA in the new lattice.

-- jim

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

David Rubin wrote:
> Gentlemen,
>
> The lattice   bmad_4160_111005.lat is my candidate for the next CLEO  run.
> On unix at /home/dlr/lat/bmad_4160_111005.lat and on cesr29 at
> [cesr.bmad.lat].
> Details of design strategy and some analysis are here
>
> http://www.lns.cornell.edu/~dlr/cesrc/bmad_4160_111005.html
>
>
> Please have a critical look.
>
> dave
>