A simulation study of the deflected neutron guide of neutron spin-echo spectrometer at CMRR

[Background] Neutron beam is provided for the spin-echo spectrometer at China Mianyang Research Reactor (CMRR) by neutron deflection at the upper part of the C32 exit of the C3 cold neutron guide. The deflected neutron guide consists of curved guide pipe and straight guide pipe with cross-section 30 mm(W) × 30 mm (H). [Purpose] This study aims to validate the design scheme of the deflected neutron guide by simulation. The parameters including the number of the channels of the curved guide, the radius of the curved guide and the supermirror factor of the deflected neutron guide. [Methods] Neutron ray-tracing package McStas version 2.5 was employed to perform Monte Carlo simulation to investigate the effects of the parameters of the deflected neutron guide on the neutron flux, energy spectrum and beam divergence at the exit and sample position of the deflected neutron guide. The parameters of the curved guide pipe such as the number of the channels, the radius, and the supermirror factor of the deflected neutron guide were studied as well. [Results] The results show that: 1) it is reasonable to divide the curved guide into 6 channels vertically; 2) the radius of the curved guide should be as large as possible when the space meet the requirements to the installation of the spectrometer; 3) the neutron flux is close to the maximum flux while the supermirror is 2.5. [Conclusions] According to simulation results, the design scheme for deflected neutron guide is achievable by using 6 channels with the radius of 40.0 m and the supermirror factor of 2.5. (authors)