THE MACHINE MODEL

For a successful operation of the SLS storage ring [1] it is crucial to keep the tolerances on linear and nonlinear imperfections as small as possible. Correction schemes have to compensate for the remaining errors. In order to simulate the imperfect SLS ring a realistic machine model has been developed utilizing the 6D code TRACY[2][3].

Horizontal and vertical alignment errors, magnet tilts, strength distortions and higher order multipoles are included. The fact that the elements are mounted on girders and the dipoles are chaining adjacent girders introduces a correlation which has to be taken into account in the simulation. The elements on the girders are assumed to have an rms aligment error of 50$\mu$m, the girders themselves 300$\mu$m and the girder joints 100 $\mu$m.

The roll of the girders is controlled to 25$\mu$rad by a hydrostatic leveling system. Individual elements are allowed to have residual rolls of 100$\mu$rad rms. In order to get a proper statistics 200 different error sequences (seeds) have been chosen in the simulation. It should be noted that all assigned errors are gaussian distributed with a cut at two sigma.