On the Influence of Crystal Geometry on the Efficiency of "Crystal Collimation" on the LHC

Future crystal based collimation system of the Large Hadron Collider is considered. We reveal that the collimation efficiency depends both on the crystal thickness and positive value of the miscut angle characterizing nonparallelity of the channeling plane and the crystal surface. In both cases the collimation efficiency is mostly determined by the number and amplitude of betatron oscillations of particles hitting the crystal the second time and can be described in terms of both beam phase space and particle deflection angle distribution after the first crystal passage. We demonstrate that a crystal thickness optimal for the collimation efficiency exist. Additionally, we prove that the miscut angle could considerably increase the inelastic nuclear interaction fraction even in the perfectly aligned crystal collimator in the UA9 experiment.