Ni-Ti supermirror coated onto a curved substrate for nested neutron-focusing optics

Abstract

Low neutron intensity is a critical problem for neutron scattering measurements at compact sources Among various other methods, reflection-based neutron-focusing devices have been developed to increase the neutron flux on samples. In this study, we utilized nested neutron-focusing optics to converge a neutron beam with large divergence. These optics consisted of nested full conical shells that were assembled from supermirror-coated thin glass sheets with an initially cylindrical form. Specifically, an optimized m = 2 Ni/Ti supermirror coating was applied to the concave sides of cylindrical thin glass substrates utilizing a dedicated DC magnetron sputtering system. A particle collimation system was also incorporated into the deposition process to achieve excellent thickness uniformity for the supermirror coating. As a result, the characterized thickness variation was within 2% on the inner sides of the curved substrates. The internal stress of the supermirror coating was effectively reduced to approximately -135 MPa under a 0.4 Pa working gas pressure. The supermirror coating provided a reflectivity of over 78% with a momentum transfer Q ranging from 0.1 to 0.45 nm−1. Consequently, the neutron flux collected by the focusing optics was enhanced by a factor of 26 compared to a conventional pinhole design according to our experimental results.