K. Lieutenant
Helmholtz-Zentrum Berlin
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Publication
Featured researches published by K. Lieutenant.
Journal of Neutron Research | 2008
K. Lefmann; Peter Kjær Willendrup; Linda Udby; Bente Lebech; Kell Mortensen; Jonas Okkels Birk; Kaspar Hewitt Klenø; Erik Knudsen; P. Christiansen; Jan Šaroun; J. Kulda; Uwe Filges; M. Konnecke; Philip L. W. Tregenna-Piggott; Judith Peters; K. Lieutenant; G. Zsigmond; Phillip M. Bentley; Emmanuel Farhi
We define a virtual neutron experiment as a complete simulation of an experiment, from source over sample to detector. The virtual experiment (VE) will ideally interface with the instrument control software for the input and with standard data analysis packages for the virtual data output. Virtual experiments are beginning to make their way into neutron scattering science with applications as diverse as instrument design/upgrade, experiment planning, data analysis, test of analysis software, teaching, and outreach. In this paper, we summarize the recent developments in this field and make suggestions for future developments and use of VEs.
Journal of Physics: Conference Series | 2014
C. Zendler; K. Lieutenant; D. Nekrassov; M Fromme
VITESS is a software widely used for simulation of neutron scattering experiments. Although originally motivated by instrument design for the European Spallation Source, all major neutron sources are available. Existing as well as future instruments on reactor or spallation sources can be designed and optimized, or simulated in a virtual experiment to prepare a measurement, including basic data evaluation. This note gives an overview of the VITESS software concept and usage. New developments are presented, including a 3D visualization of instruments and neutron trajectories, a numerical optimization routine and a parallelization tool allowing to split VITESS simulations on a computer cluster.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment | 2013
C. Zendler; K. Lieutenant; D. Nekrassov; Leo D. Cussen; Markus Strobl
Bi-spectral beam extraction combines neutrons from two different kinds of moderators into one beamline, expanding the spectral range and thereby the utilization of an instrument. This idea can be realized by a mirror that reflects long wavelength neutrons from an off-axis colder moderator into a neutron guide aligned with another moderator emitting neutrons with shorter wavelengths which will be transmitted through the mirror. The mirror used in such systems is typically several meters long, which is a severe disadvantage because it reduces the possible length of a focusing device in design concepts requiring a narrow beam at a short distance from the source, as used in many instruments under development for the planned European Spallation Source (ESS). We propose a shortened extraction system consisting of several mirrors and show that such an extraction system is better suited for combination with a feeder in an eye of the needle design, illustrated here in the context of a possible ESS imaging beamline
Optics Express | 2015
André Hilger; Nikolay Kardjilov; Ingo Manke; C. Zendler; K. Lieutenant; Klaus Habicht; John Banhart; Markus Strobl
A neutron transport system for the planned imaging instrument ODIN at the future European Spallation Source (ESS) based on neutron optical components was designed and optimized. Different ways of prompt pulse suppression were studied. The spectral performance of the optimal neutron guide configuration is presented. In addition, the influence of the gaps in the guide system needed for the required chopper configuration was investigated. Given that the requirements for an imaging instrument located on a long guide system and hosting a complex chopper system are extremely demanding in terms of spectral and divergence needs, this study can be beneficial for a wide range of instruments in various ways.
Review of Scientific Instruments | 2013
Kim Lefmann; Kaspar Hewitt Klenø; Jonas Okkels Birk; Britt Rosendahl Hansen; Sonja L. Holm; Erik Knudsen; K. Lieutenant; Lars von Moos; Morten Sales; Peter Kjær Willendrup; Ken H. Andersen
We here describe the result of simulations of 15 generic neutron instruments for the long-pulsed European Spallation Source. All instruments have been simulated for 20 different settings of the source time structure, corresponding to pulse lengths between 1 ms and 2 ms; and repetition frequencies between 10 Hz and 25 Hz. The relative change in performance with time structure is given for each instrument, and an unweighted average is calculated. The performance of the instrument suite is proportional to (a) the peak flux and (b) the duty cycle to a power of approximately 0.3. This information is an important input to determining the best accelerator parameters. In addition, we find that in our simple guide systems, most neutrons reaching the sample originate from the central 3-5 cm of the moderator. This result can be used as an input in later optimization of the moderator design. We discuss the relevance and validity of defining a single figure-of-merit for a full facility and compare with evaluations of the individual instrument classes.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment | 2014
C. Zendler; D. Nekrassov; K. Lieutenant
Abstract Ballistic neutron guides are efficient for neutron transport over long distances, and in particular elliptically shaped guides have received much attention lately. However, elliptic neutron guides generally deliver an inhomogeneous divergence distribution when used with a small source, and do not allow kinks or curvature to avoid a direct view from source to sample. In this paper, a kinked double-elliptic solution is found for neutron transport to a small sample from a small (virtual) source, as given e.g. for instruments using a pinhole beam extraction with a focusing feeder. A guide consisting of two elliptical parts connected by a linear kinked section is shown by VITESS simulations to deliver a high brilliance transfer as well as a homogeneous divergence distribution while avoiding direct line of sight to the source. It performs better than a recently proposed ellipse–parabola hybrid when used in a ballistic context with a kinked or curved central part. Another recently proposed solution, an analytically determined non-linear focusing guide shape, is applied here for the first time in a kinked and curved ballistic context. The latter is shown to yield comparable results for long wavelength neutrons as the guide design found here, with a larger inhomogeneity in the divergence but higher transmission of thermal neutrons. It needs however a larger (virtual) source and might be more difficult to build in a real instrument.
Journal of Physics: Conference Series | 2012
Markos Skoulatos; Klaus Habicht; K. Lieutenant
Horizontal focusing properties of a new neutron monochromator geometry are investigated by Monte Carlo simulations. The geometry is based on the Rowland circle, which satisfies ideal focusing conditions, as opposed to standard planar monochromator devices. For asymmetric geometries one can get optimised conditions for both intensity and energy resolution for such a Rowland monochromator, in contrast to standard planar arrays. Energy resolution gains are also found for symmetric geometries, in particular for cold neutrons. Additional advantages include a symmetric beam well centered in energy. No changes are observed in integrated intensities.
Physica B-condensed Matter | 2003
Sergey Manoshin; G. Zsigmond; K. Lieutenant; Ferenc Mezei
Soller-type collimators with supermirror coating may be used for polarisation of neutron beams. The disadvantage of such devices is a high level of gamma background and fast neutrons in the case of pulsed neutron sources. In order to increase the neutron flux, the collimator was made convergent. Generally, benders make it possible to suppress the fast neutron and gamma background completely. The combination of a bender and a convergent Soller collimator (convergent or focusing bender) is proposed for polarisation of the neutron beam for future NSE spectrometers at the cold source of ESS. Simulations and optimisation of convergent benders as neutron polarisers for NSE spectrometers are presented. The VITESS software package proved to be a powerful tool for the optimisation of polarising devices.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment | 2013
D. Nekrassov; C. Zendler; K. Lieutenant
Abstract The concept of Wavelength Frame Multiplication (WFM) was developed to extend the usable wavelength range on long pulse neutron sources for instruments using pulse shaping choppers. For some instruments, it is combined with a pulse shaping double chopper, which defines a constant wavelength resolution, and a set of frame overlap choppers that prevent spurious neutrons from reaching the detector thus avoiding systematic errors in the calculation of wavelength from time of flight. Due to its complexity, the design of such a system is challenging and there are several criteria that need to be accounted for. In this work, the design of the WFM chopper system for a potential future liquids reflectometer at the European Spallation Source (ESS) is presented, which makes use of acceptance diagrams. They prove to be a powerful tool for understanding the work principle of the system and recognizing potential problems. The authors assume that the presented study can be useful for design or upgrade of further instruments, in particular the ones planned for the ESS.
Journal of the Physical Society of Japan | 2011
Morten Sales; Sonja L. Holm; K. Lieutenant; Kim Lefmann
We have investigated the performance of a cold and a thermal neutron powder diffractometer installed at at long-pulsed source with the use of Monte Carlo ray tracing simulations. We show that the cold powder diffractometer will be a very powerful instrument when a relaxed resolution can be accepted – e.g. for magnetic studies. A comparison between a thermal powder diffractometer with and without Wavelength Frame Multiplication (WFM) show that the WFM technique can be used to achieve shorter instrument length without losing flux. The thermal powder diffractometer will be competitive with the existing high resolution powder diffractometers.