Jörg Voigt

POWTEX – the high-intensity time-of-flight diffractometer at FRM II for structure analysis of polycrystalline materials

In order to provide the large chemistry and materials science as well as the geosciences communities with a powerful tool for rapid data acquisition, a time-of-flight powder diffractometer to be installed at the new Munich reactor has been designed. The time-of-flight technique is expected to outperform a monochromator instrument by at least an order of magnitude in data acquisition time, particularly on small samples of less than a cubic centimetre. The construction of this innovative type of diffractometer utilizes modern components such as focusing super-mirror neutron guides, a four-unit high-speed disk chopper system and linear position-sensitive detectors covering a solid angle of about 2π steradian. The diffractometer design enables an easy enlargement of the focal spot size and is therefore equally well suited for the texture analysis of large geological and archaeological samples.

Approaching the true ground state of frustrated A-site spinels: A combined magnetization and polarized neutron scattering study

, macroscopic measurements evidence a ”cusp” in zero field-cooled susceptibility around13 K. Dynamic magnetic susceptibility and memory effect experiments provide results that do notconform with a canonical spin-glass scenario in this material. Through polarized neutron scatteringstudies, absence of long-range magnetic order down to 4 K is confirmed in FeAl

Beam transport and polarization at TOPAS, the thermal time-of-flight spectrometer with polarization analysis

We present the design for the polarization analysis of the future thermal time-of-flight spectrometer at the Juelich Centre for Neutron Science (JCNS) at the FRM II. TOPAS is a time-of-flight spectrometer covering a range of incident energies 20 meV < Ei < 160 meV and an angular range −3° < 2θ < 150°. A set of Fermi choppers selects the incoming energy Ei with a resolution up to 3 %. The instrument is optimized for a high flux on small samples using an elliptical neutron guide. The special feature of TOPAS is the polarization analysis. The incident polarization will be realized by means of a 3He continuously pumped polarizer, which is a downscaled version of the device developed for small angle applications at JCNS. The polarization analysis over a wide angular range demands either short distances between the sample and the analyzer or a large volume of polarized 3He. Here we propose the latter alternative to allow the study of magnetic samples and modest magnetic fields at the sample position.

Towards wide-angle neutron polarization analysis with a 3He spin filter for TOPAS and NEAT: Testing magic PASTIS on V20 at HZB

An XYZ polarization analysis solution has been developed for the new thermal time-of-flight spectrometer TOPAS [1], to be operated in the coming east neutron guide hall at the MLZ. This prototype is currently being prepared to use on NEAT at HZB [2]. Polarization Analysis Studies on a Thermal Inelastic Spectrometer, commonly called PASTIS [3], is based on polarized 3He neutron spin filters and an XYZ field configuration for the sample environment and a polarization-preserving neutron guide field. The complete system was designed to provide adiabatic transport of the neutron polarization to the sample position on TOPAS while maintaining the homogeneity of the XYZ field. This complete system has now been tested on the polarized time-of-flight ESS test beam line V20 at HZB [4]. We present results of this test and the next steps forward.