Coherent effects in crystal collimation

We present theory for coherent effects observed in crystal collimation experiments that is in good quantitative agreement with RHIC and Tevatron data. We show that coherent scattering in a bent crystal strongly amplifies beam diffusion, with an effective radiation length shortened by orders of magnitude compared to amorphous material. This coherent scattering could replace the traditional amorphous scattering in accelerator collimation systems. We predict that crystal collimation for negative particles can be as strong as for positives, unlike with channeling effect. This opens a principle way for efficient crystal steering of negative particles at accelerators. It can be demonstrated with antiproton crystal collimation at the Tevatron. We predict strong effects for the upcoming Tevatron experiment, for protons and antiprotons.