  In the framework of the project to design and test a collimation system
prototype using bent channeling crystal for cleaning of the RHIC heavy ion beam
halo, we have studied the optimal length and bending angle of a silicon (110)
single crystal proposed to be a primary element situated upstream of the
traditional heavy amorphous collimator. Besides the matters of the channeling
and collimation efficiency, we also looked into the impact the crystal may have
on the non-channeled particles that go on circulating in the ring, so as to
reduce the momentum offset of the particles scattered of the crystal.
