Bent crystal channeling has been observed with protons and fully stripped gold ions in the Relativistic Heavy Ion Collider (RHIC). Prior to 2003, a bent crystal was installed in one ring of RHIC as the first stage of a two stage collimation system. The observed channeling efficiency was approximately 25%, less than half of original predictions. We show that this is due to a difference between the model and real Twiss parameters at the crystal location and our improved understanding of the beam halo. Collimation using the crystal was unsuccessful and raised background at the STAR detector by as much as a factor of 2 because of the low channeling efficiency. We give a report of our channeling studies in RHIC and describe our experience using the bent crystal as a collimator. The results are discussed and compared to simulations and theoretical predictions.

Abstract. IHEP Protvino has pioneered the wide practical use of bent crystals as optical elements in high-energy beams for beam extraction and deflection on permanent basis since 1989. In the course of IHEP experiments, crystal channeling has been developed into efficient instrument for particle steering at accelerators, working in predictable, reliable manner with beams of very high intensity over years. Crystal systems extract 70 GeV protons from IHEP main ring with efficiency of 85% at intensity of 10 12 , basing on multi-pass mechanism of channeling proposed theoretically and realised experimentally at IHEP. Today, six locations on the IHEP 70-GeV main ring of the accelerator facility are equipped by crystal extraction systems, serving mostly for routine applications rather than for research and allowing a simultaneous run of several particle physics experiments, thus significantly enriching the IHEP physics program. The long successful history of large-scale crystal exploitation at IHEP should help to incorporate channeling crystals into accelerator systems worldwide in order to create unique systems for beam delivery. We report recent results from the research and exploitation of crystal extraction systems at IHEP.

A silicon crystal was used to channel and extract 70 GeV protons from the U-70 accelerator with an efficiency of 85.3 6 2.8%, as measured for a beam of ϳ10 12 protons directed towards crystals of ϳ2 mm length in spills of ϳ2 s duration. The experimental data follow very well the prediction of Monte Carlo simulations. This demonstration is important in devising a more efficient use of the U-70 accelerator in Protvino and provides crucial support for implementing crystal-assisted slow extraction and collimation in other machines, such as the Tevatron, RHIC, the AGS, the SNS, COSY, and the LHC.

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