Focusing neutron guide design for Engineering Materials Diffractometer at CSNS

Abstract

Engineering Materials Diffractometer (EMD) is included in Project Phase Two of the China Spallation Neutron Source (CSNS), which focuses on strain scanning, thermomechanical investigation and phase transformation analysis under different sample environments, as well as other novel industrial research for engineering materials. After a comprehensive analysis and optimization, the total length of EMD is designed to be 51.5 m where the primary and secondary flight path are 49.5 m and 2 m, respectively. The neutron optical components mainly consist of insert guides, curved guides, bandwidth choppers, straight guides (including both straight and focusing sections), slits, collimators, detectors, etc. Particularly, an individual 9 m logarithmic spiral focusing guide to optimize instrument performance was confirmed by Monte Carlo simulation with the McStas package. Under the target power of 100 kW, for high resolution mode, the resolution Δ d/d is about 0.25% for 2θ=90∘ and the neutron flux is 4.5× 106 n/cm2/s at the sample position; for high intensity mode, the neutron flux is 1.4× 107 n/cm2/s and the resolution is about 0.50%. The high instrument flexibility could allow and extend a broad of applications in materials science and engineering fields in the future. This paper will discuss the details of EMD instrument optical system design especially the focusing guide and combinations of slits.