  The compact linear collider (CLIC) requires a crab cavity to align bunches
prior to collision. The bunch structure demands tight amplitude and phase
tolerances of the RF fields inside the cavity, for the minimal luminosity loss.
Beam loading effects require special attention as it is one potential sources
of field errors in the cavity. In order to assist the amplitude and phase
control, we propose a travelling wave (TW) structure with a high group velocity
allowing rapid propagation of errors out of the system. Such a design makes the
cavity structure significantly different from previous ones. This paper will
look at the implications of this on other cavity parameters and the
optimisation of the cavity geometry.
