Laboratory for Scientific Computing and Modelling (LSM)

The new Laboratory for Scientific Computing and Modelling has been established on January 1, 2018 within PSI's research division for Nuclear Energy and Safety (NES) in collaboration with the division Research with Neutrons and Muons (NUM). It will bundle existing resources of PSI in Scientific Computing and Modelling. The topical areas of the new laboratory cover already a broad spectrum

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Recent news from LSM

3 December 2018

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Progress in non intrusive laser based measurements of gas-phase thermoscalars and supporting modeling near catalytically reacting interfaces

Heterogeneous and combined hetero/homogeneous chemical processes have attracted increased attention in many energy conversion systems, which include large scale power generation, microreactors for portable power generation, household burners, fuel processing technologies and automotive exhaust gas aftertreatment. Progress in such systems crucially depends on the development of catalysts with enhanced activity and thermal stability and on the comprehensive understanding of the fundamental processes occurring near gas solid reacting interfaces. Recent advances in non intrusive lased based measurements of gas phase thermoscalars over the catalyst boundary layer are reviewed. Such measurements, combined with theoretical analyses and numerical simulations, have fostered fundamental investigations of the catalytic and gas phase chemical processes and their coupling at industrially relevant operating conditions. The methodology for assessing local catalytic reaction rates and validating gas phase reaction mechanisms under steady conditions using 1D Raman and planar laser induced fluorescence (PLIF) of radical species, respectively, is presented first. Progress in the measurement of minor and major stable species using PLIF is outlined and the potential of this technique as a suitable method for assessing the catalytic reactivity under dynamic operating conditions is discussed. State of the art numerical modeling necessary for the interpretation of the measurements is presented in parallel with the laser based techniques. Turbulence modeling, direct numerical simulation (DNS) and near wall non intrusive measurements of species concentrations and velocity have clarified aspects of the complex interplay between interphase turbulent transport and hetero /homogeneous kinetics. Controlling parameters are the competition between the heterogeneous and homogeneous reaction pathways, diffusional imbalance of the deficient reactant, flow laminarization induced by the hot catalytic walls, and fuel leakage through the gaseous reaction zone that leads to concurrent catalytic and gas phase combustion. Experimental needs for assessing turbulent fluctuations of catalytic reaction rates as well as for investigating intrinsic instabilities (heterogeneously or homogeneously driven) are discussed. Future directions for combining in situ surface science diagnostics with in situ non intrusive gas phase thermoscalar diagnostics and for advancing current numerical tools are finally proposed.

20 July 2018

Collective magnetism in an artificial 2D XY spin system

Two-dimensional magnetic systems with continuous spin degrees of freedom exhibit a rich spectrum of thermal behaviour due to the strong competition between fluctuations and correlations. When such systems incorporate coupling via the anisotropic dipolar interaction, a discrete symmetry emerges, which can be spontaneously broken leading to a low-temperature ordered phase. However, the experimental realisation of such two-dimensional spin systems in crystalline materials is difficult since the dipolar coupling is usually much weaker than the exchange interaction. Here we realise two-dimensional magnetostatically coupled XY spin systems with nanoscale thermally active magnetic discs placed on square lattices. Using low-energy muon-spin relaxation and soft X-ray scattering, we observe correlated dynamics at the critical temperature and the emergence of static long-range order at low temperatures, which is compatible with theoretical predictions for dipolar-coupled XY spin systems. Furthermore, by modifying the sample design, we demonstrate the possibility to tune the collective magnetic behaviour in thermally active artificial spin systems with continuous degrees of freedom.
Facility: SμS, SLS

Reference: N. Leo et al, Nature Communications 9, 2850 (2018)

Read full article: here

24 May 2018


ETH Medal for outstanding MSc thesis: Beam Characterization of Low Energy Electrons from a Laser Wakefield Accelerator by N. Sauerwein

Large Research Facilities

The characteristics of low energy electrons accelerated by a laser wakefield (Laser Wakefield Acceleration LWFA) has been studied. The work included understanding the acceleration process, setting up the experiment and measuring properties like charge, divergence and energy of the accelerated electrons. The experiment included diagnostics for the laser and the electrons. In order to make high-resolution energy distribution measurements with relative errors ∆E/E of below 10%, a tunable electron spectrometer has been designed, built and characterized. A tunable permanent magnet quadrupole triplet has been designed for stigmatic focusing in a range of 5 keV to 5 MeV. The thesis can be found here: MSc Thesis N. Sauerwein