The small-angle neutron scattering instrument D33 at the Institut Laue–Langevin

The D33 small-angle neutron scattering (SANS) instrument at the Institut Laue-Langevin (ILL) is the most recent SANS instrument to be built at the ILL. In a project beginning in 2005 and lasting seven years, the concept has been developed, and the instrument designed, manufactured and installed. D33 was commissioned with neutrons during the second half of 2012, fully entering the ILL user programme in 2013. The scientific case required that D33 should provide a wide dynamic range of measured scattering vector magnitude q, flexibility with regard to the instrument resolution, and the provision of polarized neutrons and 3 He spin analysis to facilitate and expand studies in magnetism. In monochromatic mode, a velocity selector and a flexible system of inter-collimation apertures define the neutron beam. A double-chopper system enables a time-of-flight (TOF) mode of operation, allowing an enhanced dynamic q range (q(max)/q(min)) and a flexible wavelength resolution. Two large multitube detectors extend the dynamic q range further, giving q(max)/q(min) similar or equal to 25 in monochromatic mode and a very large q(max)/q(min) > 1000 in TOF mode. The sample zone is large and flexible in configuration, accommodating complex and bulky sample environments, while the position of D33 is such as to allow high magnetic fields at the sample position. The instrument is of general purpose with a performance rivalling that of D22, and is well adapted for SANS studies in scientific disciplines as diverse as solution scattering in biology and soft matter and studies of physics, materials science and magnetism. This article provides a detailed technical description of D33 and its performance and characterization of the individual components, and serves as a technical reference for users of the instrument.