Study on collimation and shielding of the back-streaming neutrons at the CSNS target

TL;DR

This study proposes a neutron collimation scheme at CSNS using beam optics and collimators, significantly reducing radiation dose rates and protecting equipment, with potential applicability to other high-power proton beam facilities.

Contribution

A novel collimation system design employing beam waists and collimators effectively reduces back-streaming neutron radiation at CSNS.

Findings

Radiation dose rate decreased significantly in the interface region

The system ensures equipment longevity, e.g., thirty years for magnets

Design can be adapted to other high-power proton beam applications

Abstract

The back-streaming neutrons from the spallation target at CSNS are very intense, and can pose serious damage problems for the devices in the accelerator-target interface region. To tackle the problems, a possible scheme for this region was studied, namely a specially designed optics for the proton beam line produces two beam waists, and two collimators are placed at the two waist positions to maximize the collimation effect of the back-streaming neutrons. Detailed Monte Carlo simulations with the beams in the two different CSNS phases show the effectiveness of the collimation system, and the radiation dose rate decreases largely in the interface section. This can ensure the use of epoxy coils for the last magnets and other devices in the beam transport line with reasonable lifetimes, e.g. thirty years. The design philosophy for such an accelerator-target interface region can also be applicable to other high-power proton beam applications.