Mike Billing and I have obtained encouraging results from calculations
of the effectiveness of the PCBETING BBI compensation knobs designed
using the lattice file generated by MJF using a fit to the phase
of the postop conditions presently in use.

Although our result is too late to be of use for the CLEO run which
just ended, we are curious to see if we can use these knobs to raise
the operational current limit as we did in the 4170 conditions (March-April/2006).
Machine studies time has been scheduled for Tuesday owl.

Below I briefly summarize the developments leading to the results obtained this week
and present an example of the level of improvement in calculated dynamic aperture.

Our plans to implement and study the closed-beta-bump approach to
BBI compensation during this past running period were first stymied by the
fact that our operating conditions were so different from the 2005 design lattice
which had served as the point of origin of the tuning which enabled us
to inject into the operating point. While this top-off operating mode eventually
led, as expected, to greater daily integrated luminosity than was achieved in
the dump-every-fill mode used in 2005, the lack of a lattice file meant we
could not design our knobs. MJF solved this problem for us in January when
he generated the 'reversed optics' file FIT_POSTOP_20070116.

After designing the knobs, we ran into a conceptual problem which was new to us.
Instead of the usual situation in which good dynamic aperture with no
opposing beam present is degraded by increasing BBI effects, this operating lattice performs
MUCH BETTER with BBI effects present. (The BBI-compensated lattice design procedure used
for 4170 was also better at high current, but only slightly.)
It took us some time to realize that we needed to turn on the PCBETING correction
at high current rather than at zero. And when we did that, the lever arm to get
20-30% higher currents was so short that the correction had very little effect.
It did help to preserve good optics to LOW positron current, but who cares.

Then, about three weeks ago, we became suspicious that the IP-correction coefficients
obtained empirically for the 4170 optics might be very wrong for the present case.
So I calculated the single-bunch IP distortion and Mike spun the knobs in
CESRV to obtain a correction for phase and beta. Indeed, these coefficients
were very different from the ones we had been using.

This past week I repeated the comparison between qtuning and PCBETING corrections we
did last year for 4170. At that time, we concluded that the dynamic aperture could be
improved from 3 sigma to 8 sigma at e+ 4 mA/bunch by using the PCBETING knobs rather than qtuning.
The new calculation indicates that the improvement in the present operating optics
would be from 4 sigma to 10 sigma. The corresponding calculation can be seen here:
http://www.lns.cornell.edu/~critten/cesr/injection/notes/30mar07/dynap_1765_1762/index.html

The calculations also show again, as Sasha likes to remind us, that the correction is
much less effective for off-energy particles.

Another interesting feature of this BBI compensation algorithm is that it
improves the dynamic aperture without improving the Welch-Temnykh B-parameter
that we use as a constraint in our lattice design procedure.

The full complement of calculations can be found here:

BBI dependence of lattice parameters
------------------------------------
Qtuning: http://www.lns.cornell.edu/~critten/cesr/injection/notes/30mar07/bunch_1765
PCBETING knobs: http://www.lns.cornell.edu/~critten/cesr/injection/notes/30mar07/bunch_1762

Dynamic aperture for all trains & bunches
-----------------------------------------
Qtuning: http://www.lns.cornell.edu/~critten/cesr/injection/notes/30mar07/dynap_1765
PCBETING knobs: http://www.lns.cornell.edu/~critten/cesr/injection/notes/30mar07/dynap_1762


-- jim

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