Proton extraction from a high-energy beam with bent crystals

Extraction with a bent crystal seems to be the only feasible option for providing the possibility for a fixed-target facility at future high-energy hadron colliders such as the LHC. If the extraction set-up is carefully designed and integrated with the beam cleaning system, a crystal could be used in a parasitic mode, i.e. without disturbing the collider experiments and using only particles that would be lost otherwise. Crystal assisted extraction has been studied at the CERN SPS. Different crystal designs and beam excitation methods have been used. Extraction efficiencies above 15% have been measured. The existence and importance of multi-pass extraction has been demonstrated with a crystal that does not allow single-pass extraction. The energy dependence of crystal extraction has been measured at three beam energies, and found to be in very good agreement with expectations. It has also been shown that the procedure for setting up extraction with a crystal is fast and easy, and that the extracted beam is very stable. During the measurements at the SPS, significant progress has been made in the understanding of the extraction process.