The collimators in the ILC serve the dual purpose of reducing the beam halo and as of a form of machine protection from potentially miss-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 [1], [2] 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.

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We investigate the electromagnetic field (e.m.) excited by a train of multiple bunches in the main superconducting linacs of the ILC. These e.m. fields are represented as a wake-field. Detailed simulations are made for the modes which constitute the long-range wake-field in new high gradient cavities. In particular, we focus our study on the modes in re-entrant cavities. Modes trapped within a limited number of cells can give rise to a significant diminution in the emittance of the beam and we pay particular attention to these modes.