Novel m = 7 supermirror - a benchmark für next generation neutron optics

In 2009 the instrument VISON @ SNS was the first beamline utilizing supermirror with index m = 7 for its neutron guide. SwissNeutronics produced the coating with a unique, excellent reflectivity (see NEWS November 2009). Recently, simulations of a parabolic guide with m = 7 for the reflectometer POLREF @ ISIS TS2 demonstrated a massive improvement in beam intensity on the sample. SwissNeutronics produced the m = 7 supermirror using the latest coating technology – a result of the continuous development. For the parabolic guide with a length of 3 m a total area of 0.38 m² was coated with supermirror m = 7. The substrate size was 35 mm × 500 mm. The figure below shows the reflectivity profiles of four arbitrarily selected samples as measured at the reflectometer TREFF @ FRM II. The coatings demonstrate an outstanding, excellent reflectivity that is reproducible for all samples. The reflectivity of the supermirrors was modelled using the standard expression from McStas resulting in a reflectivity RMcStas = 58% @ m = 7. Note that the extension of m to 7 does not compromise the reflectivity at small m values, thus a true gain in neutron intensity is realized when increasing m. In conclusion these new results establish once more the excellence and uniqueness of neutron supermirrors from SwissNeutronics opening the way to improve the reflectivity of supermirror at small m as well as to even increase m to very large values.

Fig.: Reflectivity profiles of m = 7 supermirror for the parabolic focusing guide for POLREF @ ISIS. The measurements were performed at the instrument NARZISS @ FRM-II. For comparison, the McStas formula for supermirror is plotted with R_McStas = 58% @ m = 7 – refined to the measured data.