| Summary: | Momentum collimation in a high-intensity rapid cycling synchrotron (RCS) is a very important issue. Based on the two-stage collimation principle, a combined momentum collimation method is proposed and studied in detail here. The method makes use of the combination of secondary collimators in both the longitudinal and transverse planes. The primary collimator is placed at a high-dispersion location of an arc, and the longitudinal and transverse secondary collimators are in the same arc and in the adjacent downstream dispersion-free long straight section, respectively. The particles with positive momentum deviations will be scattered and degraded by a carbon scraper and then collected mainly by the transverse collimators, whereas the particles with negative momentum deviations will be scattered by a tantalum scraper and mainly collected by the longitudinal secondary collimators. This is to benefit from the different effects of protons passing through a high atomic number material and a low atomic number material, as the former produces relatively more scattering than the latter for the same energy loss. The studies also reveal that momentum collimation is strongly dependent on the transverse beam correlation that comes from the injection painting. The relevant requirements on the lattice design are also discussed, especially for compact rings. The multiparticle simulations using both TURTLE and ORBIT codes are presented to show the physical images of the collimation method, which was carried out with the input of the RCS of China Spallation Neutron Source.
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