At the suggestion of SBP, I have applied the calculations of
pretzel orbits and dynamic effects such as those I presented
at the miniMAC to the lattice in use on the upsilon 4s just
prior to the 2001 shutdown when the superconducting IR was
installed.

After a quick look at the results, I expect that this comparison
will turn out to be instructive in our present review of
CESR-c operating conditions.

As mentioned in yesterday's CESR-c planning meeting,
the minimum e+/e- separation in HEP conditions at 5.3 GeV
was about 7.5 sigma:
http://www.lepp.cornell.edu/~critten/cesr/injection/notes/28jul05/l9a18a000_1408/P008.html
which is less than the approximately 10 sigma calculated in
present CHESS operation
http://www.lepp.cornell.edu/~critten/cesr/minimac/crittenden1/P023.html
and only slightly better than the 7 sigma calculated
in our present CESR-c conditions:
http://www.lepp.cornell.edu/~critten/cesr/minimac/crittenden1/P003.html

However, the separation shows other characteristics which are
very different between then and now. The separation normalized to
beam size was much more uniform at 5.3 GeV than it is now, ranging
from 7.5 to 14 sigma rather than from 7 to 18 sigma. The maximum separation
ranged from 1.5 cm to 3.5 cm rather than from 1.5 cm to 3.9 cm.
It is also interesting to note that the maximum separation of 3.9 cm
in the present 1.9 GeV lattice corresponds to the parasitic crossings of
the 9th train, which we have been forced to omit, ostensibly due to
ion trapping effects. At 5.3 GeV the maximum separation occured at
the electron injection point, whereas now it is near Q3W and Q8E.

Perhaps the large separations are permitted at points where the horizontal
beam size is small, meaning wall clearances can also be smaller, but
such a nonuniform behavior of the pretzel separations compared to what we
had at 5.3 GeV gives me pause. Maybe the cost to other lattice optimization
parameters of re-establishing this uniformity would not necessarily be
so great. Maybe the B parameter would turn out to remain within its
range of uncertainty.

The parasitic crossings in the present 1.9 GeV lattice also do not correlate
so closely to pretzel maxima as they did at 5.3 GeV. This is not due to any
dynamic effect, since the above plots were made with the positron current
set to zero.

The effect of turning on the BBI has so far appeared to be rather small.
However, it will be interesting to see if this remains true for
the closed orbits of the electron bunches other than t1.b1, for which
the lattice optimization was performed. Jessica Darland is looking into this.

I have also calculated the dependence of all global lattice parameters, beta
blowup, emittance growth, etc, as a function of positron beam current in
the weak/strong approximation. The 5.3 GeV lattice shows interesting behavior,
qualitatively different/opposite from that at 1.9 GeV, which I will present
in my next note.

-- Jim

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