Reduction of 400 GeV/c slow extraction beam loss with a wire diffuser at the CERN Super Proton Synchrotron

Slow extraction of a quasicontinuous flux of high-energy protons is an important requirement for many high-energy physics experiments. This extraction type is associated with an unavoidable beam loss due to scattering on the thin septum element. The energy deposition of scattering products and resulting activation place performance limits on existing and planned high-power, high-energy fixed-target proton facilities. In the $400\text{ }\text{ }\mathrm{GeV}/c$ Super Proton Synchrotron (SPS) at CERN, a diffuser (or prescatterer), comprising an array of dense wires or ribbon located upstream of the electrostatic septum, has been designed to reduce absolute losses on the septum wires. As part of a concerted effort to investigate loss reduction techniques in the SPS in view of new physics experiments, the diffuser concept was explored in numerical simulation and analytically. A prototype device has been designed, built, installed, and tested in the SPS to prove the feasibility and quantify the performance reach. In this paper, the diffuser concept is briefly recalled and design considerations for the SPS use case are presented, with the analytical considerations and simulation studies for the optimization of the material and geometry. The device design is described, and the experimental results with a beam are presented and analyzed. The results are discussed, and an outlook is given for the operational feasibility and maximum obtainable performance gain. Conclusions are drawn on the implications for the application of the concept.