Macro-particle simulation of multi-species beams in CSNS/LRBT

At the Chinese Spallation Neutron Source (CSNS), a transverse collimation system consisting of foil scrapers and 60° triplet cells in the Linac to Ring Beam Transport line (LRBT) is designed, and the scraped particles are transported to the linac development dump. For hands-on maintenance, it is important to study the beam loss in transporting the stripped protons. Due to the lack of appropriate simulation codes to track the mixed beams, a new simulation code Stripping Collimation and Mixed Beam Transport (SCOMT) was developed to tackle the problem. The macro-particles simulation code tracks simultaneously the main H−, the fully stripped proton and the partially-stripped H0 beams. It also takes into account the stripping efficiency of H− in foils, nuclear absorption, nuclear elastic scattering and multiple scattering effect, etc. The SCOMT simulations were carried out at the LRBT for the design optimization. It is found that the second-time foil traverse of both the protons and the H0 particles has an important contribution to the beam loss. The foil thickness has been optimized to reduce the total beam loss.