Observation of the influence of the crystal surface defects on the characteristics of the high energy particle beam deflected with a bent monocrystal

Nowadays bent crystals are widely applied for high energy beam steering. Some problems, like the extraction of particles from a large hadron collider, imply a high perfection of the crystal near-surface layer. In this work we have measured precisely the profiles of the beam bent by crystal, with use of nuclear emulsions. The inefficient layer measured for several crystals is as thick as /spl sime/50 /spl mu/m. There was observed also a specific mosaics of crystals near the ends, which has led to the angular perturbations of the bent beam exceeding the critical angle of channeling.