Abstract
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.
Highlights
Momentum collimation in a high-intensity proton rapid cycling synchrotron (RCS) is a very important issue, because large beam losses during rf capture and acceleration stages contribute a large portion to the total beam loss
The studies have shown two interesting effects: one is that the momentum collimation is strongly dependent on the transverse beam correlation that comes from the injection painting in the phase space; the other is that the material for the primary momentum collimator plays an important role in the collimation method
To overcome the drawbacks of the ISIS method and the J-PARC method, here we propose a new method called the combined momentum collimation method [11]
Summary
Momentum collimation in a high-intensity proton rapid cycling synchrotron (RCS) is a very important issue, because large beam losses during rf capture and acceleration stages contribute a large portion to the total beam loss. Even with a chopped beam injection, there are some longitudinal halo particles between bunches that will result in beam loss Another beam loss mechanism in the longitudinal plane is related to the particles that lose large energy in the transverse collimators but survive from there. Studied the collimation methods used in other highintensity synchrotrons [1,2,3], we found that it is difficult to design a momentum collimation system with high collimation efficiency. The studies have shown two interesting effects: one is that the momentum collimation is strongly dependent on the transverse beam correlation that comes from the injection painting in the phase space; the other is that the material for the primary momentum collimator plays an important role in the collimation method.
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