  The efficiency of the beam extraction and collimation systems in circular
accelerators with the use of the channeling effect in a bent crystal is
determined. The dependences of the extraction efficiency on the geometrical
parameters of the crystal (its length, thickness, and bending angle), the
azimuthal location of the system components, and the offset of the septum or
scraper are presented. The influence of crystal imperfections (amorphous
layers, misorientation, and torsion) on the efficiency of the systems is
considered, and their tolerances are proposed. It is shown that an extraction
efficiency of >95% can be attained over a wide energy range from 2 GeV to 7 TeV
by optimizing the crystal parameters and the positions of the system
components.
