Speaker
Description
The POLI instrument at FRM II is dedicated to carrying out experiments with polarised neutrons. Before being scattered at the sample, the neutron beam passes through a polariser. After scattering, the direction of spin polarisation can be analysed. In recent years, new polariser and analyser units have been built for an upgrade of POLI, which polarise the neutrons in situ, and will replace the earlier devices. However, compared to the previously used devices, the polarisation direction of the neutrons has changed. With the old configuration the Field was longitudinal and with the new configuration of the 3He- Polarisator there is a transversal field which is adapted by the new nutators. As before, they can be used to manipulate the direction of the spin polarisation of the neutrons after they have passed through the polariser and before they pass through the analyser. Rotatable, motor-driven Halbach ring arrays comprising NdFeB permanent magnets adiabatically rotate the field into the desired direction. It will be investigated if the new nutators show an increased field uniformity in the cryo- pad area as the old nutators. Both nutators have a modular design for greater adaptability to this and other applications: individual rings with permanent magnets can be removed or added to adapt the length of the device to a specific instrument.
The poster will feature details on the design of the nutators and their magnetic characterisation.