Polarized 3He spin-filters using MEOP for wide-angle polarization analysis

Abstract Polarized 3 He spin-filters are currently employed on a wide range of neutron instruments at the ILL, primarily for diffraction, reflectometry and fundamental physics. A wide range of recent and ongoing improvements are enabling the implementation of this technique for wide-angle polarization analysis for inelastic measurements. These include • Progress in metastability-exchange optical pumping (MEOP), resulting in on-beam polarization levels of up to 80%. • 1st generation “Pastis-1” coils for rotating the neutron polarization at the sample position, allowing for “ XYZ ” polarization analysis. • 2nd generation “Pastis-2” coils with no blind angles in the equatorial plane. • Spin-filter cells with glued silicon windows, allowing for wide-angle “banana” cells with very low background scattering. • Polarization-preserving capillaries for transferring polarized 3 He gas into the cell without manual access. The development of capillary transfer also allows for a completely new way of working with 3 He spin-filters: connecting the cells on the instruments directly to the MEOP filling station several tens of meters away and allowing for quasi-continuous operation.