Speaker
Description
The MAGiC Instrument at the European Spallation Source is a polarized neutron diffractometer dedicated to magnetism and magnetic phenomena in solid-state systems. To facilitate its science case, MAGiC will have a permanently polarized beam of cold and thermal neutrons, as well as all necessary capabilities for polarization analysis of the scattered neutrons.
The flux of the cold moderator will be polarized by a solid-state bender while neutrons from the thermal moderator will be polarized by a 3 m long channeled guide element. This polarizer is located in the middle of the 160 m long guide, at the kink section between two half-ellipses. The 80×80 mm² cross section of the polarizer is divided vertically into six separate channels using Si wafers coated by m = 4 FeSi supermirror. Due to the vertical kink, all neutrons are reflected by the wafers of one of the channels. Applying a magnetic saturation field to the supermirrors results in a spin-dependent reflectivity – one spin state is reflected, while the other is transmitted and lost. The aim is to achieve a 99 % mean polarization for 0.7 < 𝜆 < 2.3 Å.
To achieve this target value, the final design features 120 stacks of 30×30×120 mm³ NdFeB permanent magnets between long steel plates, mounted inside a vacuum housing. This results in a highly homogeneous magnetic field of 1.2 kG (0.12 T) throughout the whole 3 m long polarizer. The prototype test shows an out-of-plane field inhomogeneity below 2 %.
The challenging development and design features of the polarizer that fulfil requirements and allow safe assembly will be presented.
