Neutron Sciences Directorate

The HFIR HB-2C WAND² instrument was designed to provide two specialized data-collection capabilities: (1) fast measurements of medium-resolution powder-diffraction patterns and (2) measurements of small signals and/or diffuse scattering in single crystals. In 2018, this instrument was upgraded with a curved, ³He 2D-PSD with 120° of in-plane coverage, +/- 7.5° vertical coverage and a focal distance of 71 cm. This upgrade enables measurement of a large volume of reciprocal space for single-crystal samples, making WAND² ideal to identify magnetic propagation vectors and to study diffuse scattering and weak signals. WAND² is also a medium resolution powder diffractometer where the high flux and large continuous detector coverage allow fast data sampling, enabling parametric studies as well as studies of kinetics in phase transitions. Additionally, it can be used for time-resolved experiments studying structural transformations with short time constants or in stroboscopic mode for reversible processes. The WAND² detector (BNL120) is a seamless ³He 2D-PSD with 8*480*512 pixels. This detector has 0.4 mm subwire resolution, which yields an angular resolution of 0.03125°, better than the instrument intrinsic resolution of approx. 0.1°. The vertical focusing Ge monochromator provides high flux at the sample position. The full range of HFIR’s sample environment can be used, including cryofurnaces (4–800 K), furnaces (to 1800 K), cryostats/CCRs (to 0.06 K), and cryomagnets (to 6 T). The high flux at the sample position also allows high pressure experiments with clamp cells up to 2.5 GPa and Paris-Edinburgh Presses up to 20 GPa at room temperature.