The instrument suite of the European Spallation Source

An overview is provided of the 15 neutron beam instruments making up the initial instrument suite of the European Spallation Source (ESS), and being made available to the neutron user community. The ESS neutron source consists of a high-power accelerator and target station, providing a unique long-pulse time structure of slow neutrons. The design considerations behind the time structure, moderator geometry and instrument layout are presented. The 15-instrument suite consists of two small-angle instruments, two reflectometers, an imaging beamline, two single-crystal diffractometers; one for macromolecular crystallography and one for magnetism, two powder diffractometers, and an engineering diffractometer, as well as an array of five inelastic instruments comprising two chopper spectrometers, an inverse-geometry single-crystal excitations spectrometer, an instrument for vibrational spectroscopy and a high-resolution backscattering spectrometer. The conceptual design, performance and scientific drivers of each of these instruments are described. All of the instruments are designed to provide breakthrough new scientific capability, not currently available at existing facilities, building on the inherent strengths of the ESS long-pulse neutron source of high flux, flexible resolution and large bandwidth. Each of them is predicted to provide world-leading performance at an accelerator power of 2 MW. This technical capability translates into a very broad range of scientific capabilities. The composition of the instrument suite has been chosen to maximise the breadth and depth of the scientific impact o

Experimental evidence of mesoscopic order in the apparently amorphous glacial phase of the fragile glass former triphenylphosphite

We present a neutron scattering study over a wide range of wave vectors of the structure of the fragile glass former triphenylphosphite, with an emphasis on the recently discovered, apparently amorphous, glacial phase. Direct evidence is given by small-angle scattering data that the glacial phase has a structural organization on a mesoscopic scale $(\sim 80$ Å). Our analysis supports the interpretation of the glacial phase as a poorly crystallized phase with an unusually large unit cell and unusually small crystallites. Consequences for the theory of fragile glass-forming liquids are discussed

Scaling out the density dependence of the α relaxation in glass-forming polymers

We show that the density and temperature dependences of the α-relaxation time of several glass-forming polymers can be described through a single scaling variable X = e(ρ)/T, where e(ρ) is well fitted by a power law ρx, x being a species-specific parameter. This implies that "fragility" is an intrinsic, density-independent property of a glass-former characterizing its super-Arrhenius slowing-down of relaxations, and it leads us to propose a modification of the celebrated Angell plot.Peer reviewe

Methyl group dynamics in a confined glass

arXiv:cond-mat/0212480v2We present a neutron scattering investigation on methyl group dynamics in glassy toluene confined in mesoporous silicates of different pore sizes. The experimental results have been analysed in terms of a barrier distribution model, such a distribution following from the structural disorder in the glassy state. Confinement results in a strong decreasing of the average rotational barrier in comparison to the bulk state. We have roughly separated the distribution for the confined state in a bulk-like and a surface-like contribution, corresponding to rotors at a distance from the pore wall respectively larger and smaller than the spatial range of the interactions which contribute to the rotational potential for the methyl groups. We have estimated a distance of 7 Å as a lower limit of the interaction range, beyond the typical nearest-neighbour distance between centers-of-mass (4.7 Å).Peer reviewe

UCANS-8 in Paris Eighth International Meeting of the Union for Compact Accelerator-Driven Neutron Sources

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