that the dynamic aperture of the proposed ILC Damping Rings is dictated
primarily by the nonlinear properties of their wiggler transfer maps. Wiggler transfer maps in turn depend
sensitively on fringe-field and high-multipole effects.
Therefore it is important to have a detailed
and realistic model of the interior magnetic field, including knowledge
spatial derivatives. Modeling of these derivatives is made difficult by
presence of numerical noise. We describe how such information can be
reliably from 3-dimensional field data on a grid as provided, for
various 3-dimensional finite element field codes (OPERA-3d and Tosca)
from Vector Fields. The key ingredients
are the use of surface data and the smoothing property of the inverse
operator. We describe the advantages of
fitting on an elliptic cylindrical surface surrounding the beam..
Talk Slides: (Slides)