T-REX

Studies of excitations in quantum condensed matter strive to explore the energy range from several tenths of μeV, for the determination of small energy gaps, to several hundreds of meV, for studies of e.g. excitations in the parent compounds of high Tc superconductors or excitations into the Stoner continuum.

The asset of polarization analysis is manifold: it distinguishes different cross sections in the typically rich spectra of complex compounds and provides as such the most solid test of theory. In particular, for heterogeneous systems like magnetic thin films one may suppress the sample-inherent background from a non-magnetic substrate, which dominates the scattering. Another example comes from new multiferroics with a strong magneto-electric coupling: here either chiral magnetic structures or magnetostriction cause multiferroicity. Their fingerprints in the excitation spectra can be identified uniquely by polarization analysis.

One of the strongest scientific missions of T-REX constitutes in the study of functional materials, including catalysis metals, ion-transport materials, fuel cell membranes, nanomaterials (such as nanoporous or metal-organic frameworks for hydrogen storage, nanomembranes for filtration), thermo-electric and magneto-caloric materials, which all promise potential societal applications in fields such as new and sustainable energies, energy harvesting, environmental pollution, water purification.

Recently new smart and functionalized artificial polymers have been engineered to mimic the functional behaviour of real proteins, such as haemoglobin, at similar physiological conditions, which has further approached the two fields of soft matter and life sciences, and has enriched the scenario of fancy samples on neutron beam lines. In all such “functional” systems, be them artificial or natural, it is clear nowadays that biological functionality is governed by ps and ns dynamics, where low-energy single-particle diffusional and relaxational motions and higher-energy collective modes play equally important roles and often are even entangled to each other. Consequently, such scientific fields obviously need the very wide dynamical range of T-REX, capable of measuring both quasielastic and inelastic scattering, independently of the specific kind of sample under investigation.

The instrument length, which is nearly 170 m, defines a useful experimental wavelength band of 1.7 Å. The range of incident energy is selectable from 2 meV to 160 meV.

Therefore, the instrument is designed to accept neutrons generated at the thermal moderator of the ESS both, whilst making use of a removable cold neutrons extraction system that includes a polarizing bender for cold neutrons. To keep the polarization of cold neutrons along the entire guide, a guide field (≤ 10 G) will be integrated.

T-REX features XYZ neutron spin polarization analysis. Thermal neutron polarization is achieved with the SEOP setup [1], which has been part of development at JCNS during the last decade and has been successfully implemented for SANS and GISANS. Neutron spin analysis in XYZ is performed with the magic PASTIS setup [2], already manufactured for the TOPAS project. Specific investigations of high quality ³He cells are required [3], to achieve a long decay time of the polarization of the gas, which is a crucial for experimental investigations.

The chopper system [4] is specifically designed to make an efficient use of the flux provided by the source, by means of poly-chromatic illumination of the sample. It enables variable acquisition time frames, by means of a specially developed chopper (the FAN chopper) that suppresses selectively the sub-pulses generated by the resolution-defining choppers. The energy resolution can be adapted by quantized variation of the commensurate chopper frequencies, within the limits imposed by the secondary path uncertainty (20 mm). By limiting the beam collimation, the Q resolution can be tailored to the experimental needs, as investigated in the study of the instrumental resolution function [5].

The secondary spectrometer features a vacuum path of 3 m from sample to detector, which will cover 2.2 sr when reaching the full scope. With the angles covered by design, it will yield a dynamic range that extends from 0.05 Å^-1 < Q < 10 Å^-1, thus exploring a wide range of the reciprocal space.

[1] E. Babcock, Z. Salhi, T. Theisselmann, D. Starostin, J. Schmeissner, A. Feoktystov, S. Mattauch, P. Pistel, A. Ioffe, J. of Phys / Conf. Series 711, 012008 (2016)
[2] E. Babcock, Z. Salhi, P. Pistel, A. Ioffe, G. Simeoni, J. of Phys / Conf. Series 528, 012018 (2014)
[3] Z. Salhi, E. Babcock, A. Ioffe, P. Pistel, J. of Phys / Conf. Series 528, 012015 (2014)
[4] J. Voigt, N. Violini, T. Brückel, NIMA 741, 26 - 32 (2014)
[5] N. Violini, J. Voigt, S. Pasini, T. Brückel, NIMA 736, 31 - 39 (2014)

Anticipated typical choppers configurations were simulated by means of ray-tracing methods, showing that the elastic energy resolution (FWHM) can be freely adjusted in the range from 1% to 3% at 3meV and from 3% to 6% at 100 meV, thus providing flexible trading of resolution for flux, by increasing up to 5 times the flux at the sample.

The performance of T-REX has been benchmarked against existing world class TOF-spectrometers and shows flux gain factors between one and two orders of magnitude for maximal use of RRM, which will make the instrument very competitive when it will be online.

• Nicolò Violini
  FZ-Jülich
• Hans Kämmerling
  FZ-Jülich
• Achim Heynen
  FZ-Jülich
• Jörg Voigt
  FZ-Jülich
• Thomas Brückel
  FZ-Jülich
• Alessandro Paciaroni
  Università degli Studi di Perugia
• Francesco Sacchetti
  Università degli Studi di Perugia
• Andrea Orecchini
  Università degli Studi di Perugia &
  Consiglio Nazionale delle Ricerche
• Pietro Tozzi
  Consiglio Nazionale delle Ricerche

• E. Babcock, Z. Salhi, T. Theisselmann, D. Starostin, J. Schmeissner, A. Feoktystov, S. Mattauch, P. Pistel, A. Ioffe, J. of Phys / Conf. Series 711, 012008 (2016)
• E. Babcock, Z. Salhi, P. Pistel, A. Ioffe, G. Simeoni, J. of Phys / Conf. Series 528, 012018 (2014)
• Z. Salhi, E. Babcock, A. Ioffe, P. Pistel, J. of Phys / Conf. Series 528, 012015 (2014)
• J. Voigt, N. Violini, T. Brückel, NIMA 741, 26 - 32 (2014)
• N. Violini, J. Voigt, S. Pasini, T. Brückel, NIMA 736, 31 - 39 (2014)