Recently, the instrumentation suite operated in the neutron guide hall I has been massively upgraded. In particular the exchange of the neutron guide system now allows for substantial flux gains and optimization of instrument positions. The upgrade of the FLEXX beamline included the relocation to a guide-end position in an area of the guide hall with intrinsically low background. The primary spectrometer of FLEXX was completely rebuilt with new m=3 guides including a converging elliptical section to focus neutrons onto a virtual source. The neutrons are subsequently imaged onto a new double focussing monochromator, ensuring an increase in neutrons reaching the sample. In addition, a new velocity selector is used to remove higher order scattering which eliminates the need for filters. A polarising S-bender may be translated into the beam before the elliptical guide section where the beam is collimated, allowing the gains from focussing neutrons onto the sample to be realised for polarised measurements also.

Experiments confirmed an order of magnitude gain in intensity (at the cost of coarser momentum resolution), an improved wavelength range between 2Å and 6.5Å and demonstrated that the incoherent elastic energy widths are measurably narrower than before the upgrade. The much improved count rate allows the use of smaller single crystals samples and thus enables the upgraded FLEXX spectrometer to continue making leading edge measurements. The commissioning phase of FLEXX was completed in 2012 and the instrument is back in full user operation since mid-2012.


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