Page 87 - ILLS Annual Report 2018

MODERNISATION PROGRAMMES AND TECHNICAL DEVELOPMENTS
84-85
Neutron optics service P. Courtois (ILL)
The Neutron Optics Service carries out the maintenance, repair and replacement of neutron optics components used on the ILL’s Instruments and provides 3He spin filters for polarised neutron experiments. We also play an active part in the modernisation programmes Millennium and Endurance phase 1, producing
new optical components such as crystal monochromators and supermirrors.
In addition, an innovative research programme in the field of polarising neutron optics is currently underway
with the aim of developing advanced tools for neutron instrumentation.
The year 2018 was a special one for the Neutron Optics Service, seeing as it did the completion of the neutron spin analyser for the instrument WASP. After eight years
of intense activity, more than 3 500 double-sided
m = 2.8 Co/Ti supermirrors have been manufactured by our Multilayer Group using the Pi sputtering-deposition machine. This represents a total active area of 238 m2! The analyser is made up of 91 individual bender cassettes, each containing 37 supermirrors (figure 1). Recently mounted onto the instrument for the commissioning phase, the analyser will cover a detection angle of 90 °.
Under the framework of one of the Endurance phase 1 projects, several monochromators are under preparation. As a first step, we successfully focused our work on assembling the double-focusing HOPG monochromator for PANTHER (figure 2). This consists of an array of 165 crystals mounted in 15 columns and 11 rows, forming
an active area of 297 x 220 mm2 (width x height). The alignment of the monochromator was performed by neutron diffraction. The crystal plates have been oriented in both directions with an accuracy of 0.1 ° with respect to each other. The monochromator will be installed on PANTHER in 2019 for the commissioning phase.
A new type of Fe/Si supermirror coated on a sapphire substrate has been developed. This device results in dramatically better polarisation efficiency over a broad angular and wavelength range of the incident neutrons than that achieved using typical Fe/Si supermirrors. A broadband solid-state supermirror polariser is also under construction for the fundamental physics instrument PF1B, in order to deliver cold neutron beams with polarisation up to 99.9 %.
Figure 1
An individual bender cassette of the WASP spin analyser. Each cassette contains 37 Co/Ti polarising supermirrors and covers a detection angle of 1°.
Neutron polarisation analysers that can cover a wide angular range can also enhance the performance of neutron scattering instruments. XYZ polarisation analysis using 3He spin filters has therefore been further developed, with improvements to the performance of the so-called PASTIS system achieved by increasing the 3He relaxation time up to 100 hours. The design of the new system, PASTIS3, is now complete and the first prototype is being constructed for the triple-axis spectrometer IN20.
Finally, to cope with the expected rise in demand for 3He spin filters, we have begun work on upgrading the filling station known as ‘Tyrex’, in order to increase its production capacity by a factor of two. This project is on track and we expect to complete refurbishment during the long reactor shutdown in 2019–2020.
Figure 2
The double-focusing HOPG monochromator for the Endurance phase 1 project PANTHER. The horizontal and vertical curvatures can be varied independently.
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