Abstract
We have developed a variable focusing system for neutrons that allows varying the vertical and horizontal beam size at the sample position independently. It is based on a focusing parabolic neutron guide coated with supermirror m = 6 times the critical angle of reflection of Ni. The divergence of the incident beam is adjusted by solid-state collimators with horizontally and vertically arranged absorbing blades. The performance of the prototype set-up has been benchmarked at the beamline BOA at SINQ confirming the expected behavior. In particular we show that the beam size at the sample position can be varied between 0.6 and 2 mm without exchanging the focusing guide or by introducing a beam-defining aperture between the exit of the guide and the sample, i.e. the beam size can be adapted more than half a meter away from the sample.
Highlights
The investigation of novel materials using neutron scattering techniques is challenging because these materials are often only available in small quantities, e.g. encompassing a volume of a few mm3
The suppression of the plateau is most efficient for incident beams with low divergence, which yield the best focused beams at the sample position
We have introduced a focusing system for neutrons that allows the selection of the vertical and horizontal beam size at the sample position over a wide range by means of a combination of two collimation stages and a 500 mm long focusing parabolic neutron guide
Summary
The investigation of novel materials using neutron scattering techniques is challenging because these materials are often only available in small quantities, e.g. encompassing a volume of a few mm3. While adjusting the beam size at the sample with Montel mirrors [6] is straightforward using an aperture at the focal point at the entrance of the mirror [6], the selection of the beam size using elliptic or parabolic guides is more complicated and essentially given by the design of the optics [7].
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