Upgrade of the NRSE option

The upgrade of the primary spectrometer of FLEXX has resulted in an order-of-magnitude increase of the neutron flux at the sample, originating from improved guide coating, novel focusing neutron optics and a double-focusing monochromator, thus exploiting a larger beam cross section. To take full advantage of the modified beam characteristics, the new RF flippers of the NRSE option, which have been built in cooperation with MPI for Solid State Research, Stuttgart, feature larger beam windows. Polarized neutrons are provided by a compact S-bender installed in the low-divergence section of the primary beam path at the end of the curved neutron guide. A Heusler analyzer with variable horizontal focusing and fixed vertical focusing further improves the count rates by enhancing the transmission through the secondary spectrometer.

During the course of the upgrade the design of the spectrometer arms of the NRSE option was optimized allowing for larger scattering angles (±120°) for elastic Larmor diffraction experiments and inelastic measurements. A new, more compact μ-metal shielding guarantees a better shielding of the field-free area between the NRSE coils. The new NRSE coils allow for larger maximum tilt angles of up to 50°, giving access to steeper dispersion relations, and for larger maximum frequencies, giving access to larger spin-echo times. In total, the detector count rate for the spin echo option has been increased by a factor of 15, while at the same time the accessible parameter space has been significantly improved [1].



[1] F. Groitl, T. Keller, D.L. Quintero-Castro, K. Habicht, Neutron resonance spin-echo upgrade at the three-axis spectrometer FLEXX, Rev. Sci. Instrum. 86 (2015), 025110.