CERN Linac4 Chopper Dump: Operational Experience and Future Upgrades

The Chopper Dump in the Linac4 accelerator at CERN is a beam-intercepting device responsible for the absorption of the 3 MeV H⁻ ion beam produced by the Linac4 source and deflected upstream by an electromagnetic chopper. It allows a portion of the beam, which would otherwise fall into the unstable region of the radiofrequency buckets in the Proton Synchrotron Booster, to be dumped at low energy with minimal induced radiation. It may also be used to absorb the entire beam. With peak currents of 25 to 45 mA and shallow penetration, this results in large deposited energy densities, thermal gradients and mechanical stresses. Additional constraints arise from geometric integration, vacuum and radiation protection requirements. Material selection, beam-matter interaction studies and thermo-structural analyses are important aspects of the design process. The Chopper Dump underwent modification in 2019 following observed material degradation in the original version of the device. The experience gained, modifications made and observations noted since then are detailed herein. Against this background, the design and analysis of an upgraded device, intended to cope with future operational conditions, is outlined and discussed.