Advanced on-target beam monitoring for spallation sources

The correct distribution of the incident proton beam density is crucial for the safe operation of high-power spallation targets. In all installations the proton beam footprint has to be monitored and any deviation from tight reference values must invariably lead to the prompt interruption of the irradiation. Based on several years’ experience with the dedicated optical system VIMOS at the Paul Scherrer Institute (PSI) neutron spallation source SINQ, issues, which turned out important and difficult, are highlighted.