Summary Report
Henry A. Thiessen
LA-UR-02-3315
Los Alamos National Laboratory
Los Alamos, New Mexico 87545 USA
Abstract. We discuss here the status of dynamic aperture calculations for the various machines discussed at this
workshop. We recommend that these calculations be extended to include all magnet field errors and alignment errors as
quickly as possible.
THE CONVENOR'S VIEW
At this meeting, we saw many new, innovative
lattices proposed for machines either in design phase
or in construction. These lattices have many essential
features for operation at high current with low losses
including explicit collimation schemes, avoiding
transition, and intentional eta function manipulation to
allow production of short pulses, etc. Most of these
lattices have larger acceptance than their predecessors.
Dynamic aperture is an important issue to be
considered before committing to a final design of any
of these machines.
We saw numerous studies of the dynamic aperture
of the intrinsic lattices, /.e., in the absence of magnet
field and alignment errors. Tune issues, placement of
chromaticity sextupoles, and nearby structural
resonances all play important roles in limiting the
dynamic aperture seen. Most of the dynamic aperture
studies shown at this workshop did not include magnet
errors, although all participants acknowledged that
such calculations were planned for the future.
However, there was a general trend. The more
magnet imperfections that were included, the smaller
was the dynamic aperture. Indeed, the Fermilab Proton
Driver talks showed that the differences in dynamic
aperture among the various lattice designs tended to
disappear when systematic errors of quadrupoles were
included in the tracking.
The Los Alamos team found that the dynamic
aperture of their lattices was marginal when all magnet
errors - random, systematic, and alignment - were
included in the tracking1. The solution needed at Los
Alamos is to build better quadrupole magnets2.
This reminds us of the early years of operation of
the original Fermilab Main Ring. For this machine, the
dynamic aperture was found to be very small at
injection time, due to unexpected and unanalyzed
remnant sextupole and decapole components in the
dipole fields. The heroic efforts of many people and on
the order of a year's time was needed to correct the
dynamic aperture of the Main Ring. We do not want to
repeat this exercise.
In contrast, the Fermilab Main Injector dynamic
aperture was studied in advance of construction with
all errors included. A decision was made to build
better dipoles than in the Main Ring, and to operate
these dipoles at a higher injection field. Many of the
quadrupoles were reused. Tracking with worst-case
errors showed that the dynamic aperture at injection
time exceeded the physical aperture. Turnon of the
Main Injector was rapid and uneventful, as we wish
for future machines.
The message is clear - do a dynamic aperture study
with all errors in advance of construction. Either
provide sufficient quality magnets, or a suitably
designed correction scheme such that the dynamic
aperture can be made larger than the required aperture.
In most cases, the critical time in the accelerator cycle
is near injection time, when the required aperture is
largest and magnet field errors may be largest.
REFERENCES
1. Filippo Neri, Martin Schulze, Dave Johnson, Peter
Schwandt, "Transverse Tracking of the AHF Rings", in
this workshop proceedings.
2. Martin Schulze, David E. Johnson and Ben Pilchard,
Filippo Neri and Arch Thiessen, "Magnets that Meet
Tracking Requirements for AHF", in this workshop
proceedings.
3. "The Fermilab Main Injector Technical
Handbook" 1995, private communication.
CP642, High Intensity and High Brightness Hadron Beams: 20th ICFA Advanced Beam Dynamics Workshop on
High Intensity and High Brightness Hadron Beams, edited by W. Chou, Y. Mori, D. Neuffer, and J.-F. Ostiguy
© 2002 American Institute of Physics 0-7354-0097-0/02/$ 19.00
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Design