The Ibaraki prefecture materials design diffractometer for J-PARC-Designing neutron guide

Ibaraki prefecture materials design diffractometer of J-PARC needs a neutron guide to increase beam intensity without sacrificing measurements of powder diffraction with good resolution, PDF analysis and small angle scattering. Non-parallel guides including elliptical ones have been compared with a linear-straight guide using the McStas simulation. The elliptical guide having the exit focal points away behind the sample position is available to increase the neutron flux at the sample but gives a slight lowering of the instrumental resolution. This elliptical guide gives also Garland peaks at short wavelengths that may give large ambiguities in powder diffraction measurements. Therefore, the linear-straight guide is considered as the best choice for this instrument to keep a good resolution and also a relatively high flux.