Computations of wakefields in the ILC collimators

The collimators in the ILC serve the dual purpose of reducing the beam halo and as of a form of machine protection from potentially mis-steered beams. However, there is a significant wakefield in the immediate vicinity of the beam caused by their presence. It is important to be able to predict this short-range wake-field and the extent which it dilutes the emittance of the beam. We extend the previous analysis of wake-fields in collimators to realistic short bunches applicable to the ILC. We achieve these results using the finite difference code GdfidL. The angular wake is decomposed into its constituent components for rectangular collimators and compared with their circular collimator counterparts. Comparisons are made between these simulations, existing analytical models, and experimental results.