Design of the two-stage collimation system for CSNS/RCS

The transverse collimation system of the Chinese Spallation Neutron Source (CSNS) Rapid Cycling Synchrotron (RCS) is expected to have a collimation efficiency of over 95%. The transverse collimation system is a two-stage collimation system, including a primary collimator and some secondary collimators. Here, the collimation efficiency of CSNS/RCS is deduced in the 2D case. The relationship between the collimation efficiency with phase advances and scattering angle is clearly shown. Finally, collimators are optimized with ORBIT code.