Journal of Neutron Research - Volume 17, issue 1

Authors: Carlile, Colin

Article Type: Other

DOI: 10.3233/JNR-130008

Citation: Journal of Neutron Research, vol. 17, no. 1, pp. 1-1, 2014

Authors: Lefmann, Kim | Šaroun, Jan

Article Type: Other

Abstract: The name MCNSI7 was an acronym for “Monte Carlo Simulations of Neutron Scattering Instruments in FP7”. MCNSI7 was a network under the FP7 neutron project NMI3, 2008–2012. The main activities of this network was to hold annual meetings for the neutron simulator community and to arrange a satellite workshop to the ECNS2011 conference in Prague. The workshop attracted 35 participants from 10 countries.

DOI: 10.3233/JNR-130009

Citation: Journal of Neutron Research, vol. 17, no. 1, pp. 3-3, 2014

Authors: Farhi, E. | Debab, Y. | Willendrup, P.

Article Type: Research Article

Abstract: We present a new tool, iFit, which uses a single object class to hold any data set, and provides an extensive list of methods to import and export data, view, manipulate, apply mathematical operators, optimize problems and fit models to the data sets. Currently implemented using Matlab® , the toolbox is lightweight and comes with an extensive documentation based on tutorials with ready-to-run examples for each operator. Provided with the package is a set of optimization algorithms, which we have benchmarked in order to recommend the ones that provide the best success rate for both continuous and noisy problems. These …optimizers can then be used to fit models onto data objects, and optimize McStas instrument simulations. As an application, we propose a methodology to analyse neutron scattering measurements in a pure Monte Carlo optimization procedure using McStas and iFit. As opposed to the conventional data reduction and analysis procedures, this new methodology is able to intrinsically account for most of the experimental effects, and results in the sample only model, de-convolved from the instrument. Show more

Keywords: Numerical analysis, optimization, Monte Carlo, neutron scattering

DOI: 10.3233/JNR-130001

Citation: Journal of Neutron Research, vol. 17, no. 1, pp. 5-18, 2014

Authors: Manoshin, S. | Rubtsov, A. | Bodnarchuk, V. | Mattauch, S. | Ioffe, A.

Article Type: Research Article

Abstract: Latest developments of the polarized neutron suite in the VITESS simulation package allowed for simulations of time-dependent spin handling devices (e.g. radio-frequency (RF) flippers, adiabatic gradient RF-flippers) and the instrumentation built upon them (NRSE, SESANS, MIEZE, etc.). However, till now the magnetic field distribution in such devices have been considered as “ideal” (sinusoidal, triangular or rectangular), when the main practical interest is in the use of arbitrary magnetic field distributions (either obtained by the field mapping or by FEM calculations) that may significantly influence the performance of real polarized neutron instruments and is the key issue in the practical …use of the simulation packages. Here we describe modified VITESS modules opening the possibility to load the magnetic field 3-dimensional space map from an external source (file). Such a map can be either obtained by direct measurements or calculated by dedicated FEM programs (such as ANSYS, MagNet, Maxwell or similar). The successful use of these new modules is demonstrated by a very good agreement of neutron polarimetric experiments with performance of the spin turner with rotating magnetic field and an adiabatic gradient RF-flipper simulated by VITESS using calculated 3-dimensional field maps (using MagNet) and magnetic field mapping, respectively. Show more

Keywords: VITESS, Monte Carlo simulation, magnetic field distribution, polarized neutron suite

DOI: 10.3233/JNR-130002

Citation: Journal of Neutron Research, vol. 17, no. 1, pp. 19-26, 2014

Authors: Knudsen, E.B. | Tranum-Rømer, A. | Willendrup, P.K. | Christiansen, P. | Lefmann, K.

Article Type: Research Article

Abstract: Ray-tracing of polarized neutrons faces a challenge when the neutron propagates through an inhomogeneous magnetic field. This affects simulations of novel instruments using encoding of energy or angle into the neutron spin. We here present a new implementation of propagation of polarized neutrons within the McStas simulation package and show that it outperforms the de-facto standard method implemented in the NISP package by Seeger and Daemen. We include simulation of a simplified model of a spin-echo instrument, including a simple virtual experiment.

Keywords: Ray-tracing, neutron spin-echo, Larmor precession, McStas, algorithms

DOI: 10.3233/JNR-130003

Citation: Journal of Neutron Research, vol. 17, no. 1, pp. 27-34, 2014

Authors: Willendrup, P. | Farhi, E. | Knudsen, E. | Filges, U. | Lefmann, K.

Article Type: Research Article

Abstract: The McStas neutron ray-tracing simulation package is a collaboration between Risø DTU, ILL, University of Copenhagen and the PSI. During its lifetime, McStas has evolved to become the world leading software in the area of neutron scattering simulations for instrument design, optimisation, virtual experiments. McStas is being actively used for the design-update of the European Spallation Source (ESS) in Lund. This paper includes an introduction to the McStas package, recent and ongoing simulation projects. Further, new features in releases McStas 1.12c and 2.0 are discussed.

Keywords: Neutron, instruments, Monte Carlo, ray-tracing

DOI: 10.3233/JNR-130004

Citation: Journal of Neutron Research, vol. 17, no. 1, pp. 35-43, 2014

Authors: Lieutenant, K. | Zendler, C. | Manoshin, S. | Fromme, M. | Houben, A. | Nekrassov, D.

Article Type: Research Article

Abstract: The VITESS software package is a useful tool for the development of neutron scattering instruments. Although initially intended to assist in designing new instruments for the European Spallation Source, it can also be used effectively to simulate complex instrument set-ups at continuous, short-pulsed or long-pulsed sources. This article outlines the conceptual design of the VITESS program and describes new features included in the most recent version of the package, VITESS 2.10. These include the possibility to split parts of the simulation into several threads which improves efficiency on multi-processor computers. New components for elliptic mirrors, lenses and beam-stops have been …added. The neutron guide module now permits the visualization of neutron trajectories. Results of the simulation of the EXED instrument at Helmholtz-Zentrum Berlin are presented as an example of the program's use. New features implemented in release 2.11 or planned for release 3 are described. Show more

Keywords: VITESS, Monte Carlo simulation, neutron scattering instrumentation

DOI: 10.3233/JNR-130005

Citation: Journal of Neutron Research, vol. 17, no. 1, pp. 45-51, 2014

Authors: Šaroun, J. | Beran, P.

Article Type: Research Article

Abstract: Recent development of the program package RESTRAX permitted us to carry out numerical optimizations of two generic types of powder diffractometers for the envisaged long-pulse structure of the European Spallation Source (ESS), namely a constant wavelength instrument equipped with a crystal monochromator (CM) and a narrow band time-of-flight (ToF) diffractometer. The aim was to compare properties of these two conceptually different instrument types. Optimization using particle swarm algorithm was carried out in the space of 10–15 free parameters for each instrument, while keeping the source, beam extraction optics, sample and detector fixed at the same values for both setups. The …optimum performance was defined by the figure of merit based on the evaluation of complete simulated α-SiO2 diffractograms. As a result, we arrived at configurations yielding similar average resolution, but large difference (up to a factor of 40) in neutron intensity in favour of the ToF concept. The CM option is however competitive with ToF in terms of spectral flux density and instantaneous flux, which may find use in stroboscopic measurements or in-situ experiments under pulsed sample environments with millisecond duty times. Show more

Keywords: Neutron diffractometer, long-pulse spallation source, Monte Carlo, optimization

DOI: 10.3233/JNR-130006

Citation: Journal of Neutron Research, vol. 17, no. 1, pp. 53-62, 2014

Authors: Farhi, E. | Monzat, C. | Arnerin, R. | van Vuure, T. | Castán-Guerrero, C. | Hennane, C. | Harraud, P.A. | Campioni, G. | Fuard, S. | Ollivier, J. | Willendrup, P.

Article Type: Research Article

Abstract: We present new McStas components Virtual_mcnp_input and Virtual_tripoli4_input, Virtual_mcnp_output and Virtual_tripoli_output to be used as interface for the MCNP and Tripoli neutron transport codes. Similarly, the new Lens component can be used to describe any refracting material set-up, including lenses and prisms. A new library for McStas adds the ability to describe any geometrical arrangement as a set of polygons. This feature has been implemented in most sample scattering components such as Single_crystal, Incoherent, Isotropic_Sqw (liquids/amorphous/powder), PowderN as well as in Guide_anyshape component for reflecting or absorbing complex set-up. The PSD_Detector component models a neutron absorbing gas volume, taking into …account for instance the penetration depth and the associated parallax effect, the charge cloud generated at the absorption location. This gas volume can be enclosed in a scattering material in order to model the absorption and scattering in the detector housing, prior to the actual detection. An extended model of the IN5b time-of-flight spectrometer at the Institut Laue Langevin is used to simulate vanadium and powder diffractograms, making use of the gas detector component. Show more

Keywords: Monte-Carlo, neutron scattering, neutron refracting lens, neutron gas detector, geometry file, neutron transport, time of flight spectrometer

DOI: 10.3233/JNR-130007

Citation: Journal of Neutron Research, vol. 17, no. 1, pp. 63-74, 2014