Instrumental setup for polarized neutron scattering experiments

Neutron scattering with polarization analysis is a powerful tool to determine magnetic structures and excitations. A common setup is to mount the sample at the center of a Helmholtz-type coil which can provide a magnetic field of any direction at the sample position and also a guide field along the neutron flight paths around the sample. We have extended the standard setup to a combination of a large vacuum tank surrounded by the electrical coils. The vacuum tank eliminates the air scattering, and we can use the polarization analysis down to the lowest accessible momentum transfers. The coils themselves also show some appealing features: In contrast to the classic (symmetric) coil distribution, we use an asymmetric setup which gives the advantage of a larger scattering window. Due to a more sophisticated current distribution, this modified Helmholtz coil does not need to be rotated for different scattering conditions. The whole setup is currently being constructed at the IN12 instrument, a three-axis spectrometer for cold neutrons, operated by FZ Juelich in collaboration with CEA Grenoble as a CRG-B instrument at the Institut Laue Langevin in Grenoble