Performance of the closed orbit feedback systems with spatial model mismatch

Closed orbit feedback (COFB) systems at synchrotrons used for the global orbit correction rely on the
pseudoinversion of the orbit response matrix (ORM). A mismatch between the model ORM used in the
controller and the actual machine ORM can affect the performance of the feedback system. In this paper,
the typical sources of such model mismatch such as acceleration ramp ORM variation, intensity-dependent
tune shift and beta beating are considered in comprehensive simulation studies. Their effect on the
performance and the stability margins are investigated for both the slow and fast regimes of a COFB system
operation. The spectral radius stability condition is utilized instead of the small gain theorem to arrive at the
theoretical limits of COFB stability. Comparisons with simulations for SIS18 of GSI and experiments at
the cooler synchrotron (COSY) in the Forschungzentrum Jülich (FZJ) are presented.