Orateur
Description
Summary
A hybrid design for a FFAG accelerator has been developed which successfully exploits
strong-focusing to provide tune and envelope control, and then suppresses variations
with beam energy using weak focusing. The net effect is to enlarge the momentum
space which remains within the stable range in tune space. The conceptual approach
is easy to understand, but difficult to simulate accurately with the limited
capability of present optics codes, but work is in progress to present a more
accurate representation.
With stabilized tunes, this FFAG behaves more like a synchrotron with multiple
energies available for extraction and use, and with the attractive low-loss feature
characteristic of synchrotrons. With its fixed fields, the magnets and power
supplies are simple and this machine can be effectively operated continuously with
high output beam current which is the noted strength of the cyclotron. The designs
here specifically apply only normal conducting fields and still attain carbon therapy
kinetic energies of 400 MeV/nucleon. Also like the synchrotron and unlike the
cyclotron, there are multiple places to extract beam supporting multiple treatment
rooms or other applications. This machine exhibits a reasonable dynamic aperture
and performance due to the use of only linear gradient (quadrupole) and constant
(dipole) fields which are known for their stable equations of motion.
Preliminary tracking studies at the injection energy using MAD indicate a reasonable,
full, geometric dynamic aperture of 10-20 pi mm-mr. Although almost 3 orders of
magnitude less than the comparable muon accelerator, which requires an exceptionally
large acceptance for muons, this value is yet more than acceptable for the small
emittances associated with proton and carbon beams.
