Near-wall wakefields for optimized geometry of TTF 2 collimator

TESLA Reports 2003 11 pp. (2003).
Wakefields excited in the small aperture collimators may damage the beam. As pointed out by K. Bane and P. Morton the wakefields can be reduced considerably by tapering the steps and using the “step+taper” collimator geometry. The optimisation of this kind of geometry for TTF 2 collimators with different apertures is carried out in the paper. For the optimal geometries the non-linear near-wall wakefields are calculated. The numerical results are confirmed by comparison with analytical estimations for the fully tapered collimator in inductive regime.