Demonstration of slow extraction loss reduction with the application of octupoles at the CERN Super Proton Synchrotron

Abstract

The powering of octupoles during third-integer resonant slow extraction has been studied and recently tested with the beam at the CERN Super Proton Synchrotron (SPS) in order to increase the extraction efficiency and reduce the induced radioactivity along the extraction straight. The octupoles distort the particle trajectories in phase space in such a way that the extracted separatrix is folded, which decreases the particle density impinging the wires of the extraction septum at the expense of increasing the extracted beam emittance. During experimental SPS machine studies a reduction of over 40% in the specific (per extracted proton) beam loss measured at the extraction septum was achieved. In this paper, the prerequisite studies needed to safely deploy the new extraction scheme in a limited time-frame are described, the experimental results are presented and an outlook given toward the next steps to bring slow extraction with octupoles into routine operation.