Development of the computational software tools to automate the computational analyses of fusion relevant benchmarks

The software tool was developed to automate the validation of the evaluated neutron cross sections files against the benchmarks which provide the differential responses. Specifically it was implemented for the energy and time distributions of neutrons and γ-ray spectra measured with the D-T and $^{252}$Cf(s.f.) neutron sources and simulated by Monte Carlo code MCNP. The master script modifies the MCNP input deck by selecting the desired evaluation, runs MCNP and compares the calculated spectra with measured ones in user defined intervals. The criteria chi-squared, either for intervals or for the whole measured range, was selected to judge about the performance of the evaluated cross section data library. The application of the developed tools for the validation of the ENDF/B-VIII.0, FENDL-3.1d, JEFF.3.3 and JENDL-4.0u libraries against the iron spherical benchmarks with $^{252}$Cf and D-T sources has shown that JEFF-3.3 should be considered as superable over all others libraries for the task of the neutron transport. However all tested libraries underestimate the neutron induced γ- rays leakage from bulk iron by factor of two. The reliability of the validation conclusions was strengthened by inter-comparison of the similar benchmarks but carried out in different labs

Quiescent prominences in the era of ALMA : simulated observations using 3D whole-prominence fine structure model

We use the detailed 3D whole-prominence fine structure model to produce the first simulated high-resolution ALMA observations of a modeled quiescent solar prominence. The synthetic brightness temperature and optical thickness maps shown in the present paper are produced using a visualization method for the sub-millimeter/millimeter radio continua synthesis. We have obtained the simulated observations of both the prominence at the limb and the filament on the disk at wavelengths covering a broad range which encompasses the full potential of ALMA.We demonstrate here to what extent the small-scale and large-scale prominence and filament structures will be visible in the ALMA observations spanning both the optically thin and thick regimes. We analyze the relationship between the brightness and kinetic temperature of the prominence plasma. We also illustrate the opportunities ALMA will provide for studying the thermal structure of the prominence plasma from the cool prominence fine structure cores to the prominence-corona transition region. In addition, we show that the detailed 3D modeling of entire prominences with their numerous fine structures will be important for the correct interpretation of future ALMA prominence observations.PostprintPeer reviewe

Quiescent prominences in the era of ALMA. II. Kinetic temperature diagnostics

Funding: UK STFC, the Leverhulme Trust, and NASA (D.H.M.)We provide the theoretical background for diagnostics of the thermal properties of solar prominences observed by the Atacama Large Millimeter/submillimeter Array (ALMA). To do this, we employ the 3D Whole-Prominence Fine Structure (WPFS) model that produces synthetic ALMA-like observations of a complex simulated prominence. We use synthetic observations derived at two different submillimeter/millimeter (SMM) wavelengths—one at a wavelength at which the simulated prominence is completely optically thin and another at a wavelength at which a significant portion of the simulated prominence is optically thick—as if these were the actual ALMA observations. This allows us to develop a technique for an analysis of the prominence plasma thermal properties from such a pair of simultaneous high-resolution ALMA observations. The 3D WPFS model also provides detailed information about the distribution of the kinetic temperature and the optical thickness along any line of sight. We can thus assess whether the measure of the kinetic temperature derived from observations accurately represents the actual kinetic temperature properties of the observed plasma. We demonstrate here that in a given pixel the optical thickness at the wavelength at which the prominence plasma is optically thick needs to be above unity or even larger to achieve a sufficient accuracy of the derived information about the kinetic temperature of the analyzed plasma. Information about the optical thickness cannot be directly discerned from observations at the SMM wavelengths alone. However, we show that a criterion that can identify those pixels in which the derived kinetic temperature values correspond well to the actual thermal properties in which the observed prominence can be established.Publisher PDFPeer reviewe

Ab initio Determination of Phase Stabilities of Dynamically Disordered Solids: rotational C2 disorder in Li2C2

The temperature-induced orthorhombic to cubic phase transition in Li2C2is a prototypical ex-ample of a solid to solid phase transformation between an ordered phase, which is well describedwithin the phonon theory, and a dynamically disordered phase with rotating molecules, for which the standard phonon theory is not applicable. The transformation in Li2C2 happens from a phase with directionally ordered C2 dimers to a structure, where they are dynamically disordered. We provide a description of this transition within the recently developed method (Klarbring et al.,Phys.Rev. Lett. 121, 225702 (2018)) employing ab initio molecular dynamics (AIMD) based stress-strain thermodynamic integration on a deformation path that connects the ordered and dynamically disordered phases. The free energy difference between the two phases is obtained. The entropy that stabilizes the dynamically disordered cubic phase is captured by the behavior of the stress on the deformation path

Effect of particle size on functional and mechanical properties of single crystals of iron-based FeNiCoAlNb alloy

It is shown that [001]-single crystals Fe-28%Ni-17%Co-11.5%Al-2.5Nb (at. %) alloy aged at T=973 K, 1−20 hours are observed γ'-phase particle size of 3-25 nm, which give rise to thermoelastic of the γ-α′ martensitic transformation. The effect of size of γ'-phase particle on the critical stress of high temperature phase, the temperature range of superelasticity and the mechanical hysteresis are investigated

Na–Ni–H phase formation at high pressures and high temperatures: hydrido complexes [NiH5]3– versus the perovskite NaNiH3

The Na-Ni-H system was investigated by in situ synchrotron diffraction studies of reaction mixtures NaH-Ni-H-2 at around 5, 10, and 12 GPa. The existence of ternary hydrogen-rich hydrides with compositions Na3NiH5 and NaNiH3, where Ni attains the oxidation state II, is demonstrated. Upon heating at similar to 5 GPa, face-centered cubic (fcc) Na3NiH5 forms above 430 degrees C. Upon cooling, it undergoes a rapid and reversible phase transition at 330 degrees C to an orthorhombic (Cmcm) form. Upon pressure release, Na3NiH5 further transforms into its recoverable Pnma form whose structure was elucidated from synchrotron powder diffraction data, aided by first-principles density functional theory (DFT) calculations. Na3NiH5 features previously unknown square pyramidal 18- electron complexes NiH53-. In the high temperature fcc form, metal atoms are arranged as in the Heusler structure, and ab initio molecular dynamics simulations suggest that the complexes are dynamically disordered. The Heusler-type metal partial structure is essentially maintained in the low temperature Cmcm form, in which NiH53- complexes are ordered. It is considerably rearranged in the low pressure Pnma form. Experiments at 10 GPa showed an initial formation of fcc Na3NiH5 followed by the addition of the perovskite hydride NaNiH3, in which Ni(II) attains an octahedral environment by H atoms. NaNiH3 is recoverable at ambient pressures and represents the sole product of 12 GPa experiments. DFT calculations show that the decomposition of Na3NiH5 = NaNiH3 + 2 NaH is enthalpically favored at all pressures, suggesting that Na3NiH5 is metastable and its formation is kinetically favored. Ni-H bonding in metallic NaNiH3 is considered covalent, as in electron precise Na3NiH5, but delocalized in the polyanion [NiH3](-).Funding Agencies|Swedish Research Council (VR)Swedish Research Council [2019-05551]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at at Linkoping University (Faculty Grant SFO-Mat-LiU) [200900971]; Carl Tryggers Stiftelse (CTS) [16:198, 17:206]</p