  The Fermilab crystal-extraction experiment E853 at Tevatron was simulated by
Monte Carlo code CATCH [1] tested earlier in the CERN-SPS experiment [2-4].
Predictions for the extraction efficiency, angular scans and extracted beam
profiles are presented. Several ideas are proposed and tested by the
simulation, how to get in E853 the key information of the extraction
experiment: the "septum width" of a crystal and dependence of extraction
efficiency on it, the impact parameters of protons at crystal, and the
contribution of the first and multi passes to the extraction. The ways to
optimize E853 are analyzed.
