SDSS DR7 superclusters. Morphology

We study the morphology of a set of superclusters drawn from the SDSS DR7. We calculate the luminosity density field to determine superclusters from a flux- limited sample of galaxies from SDSS DR7, and select superclusters with 300 and more galaxies for our study. The morphology of superclusters is described with the fourth Minkowski functional V3, the morphological signature (the curve in the shapefinder's K1-K2 plane) and the shape parameter (the ratio of the shapefinders K1/K2). We investigate the supercluster sample using multidimensional normal mixture modelling, and use Abell clusters to identify our superclusters with known superclusters and to study the large-scale distribution of superclusters. The superclusters in our sample form three chains of superclusters; one of them is the Sloan Great Wall. Most superclusters have filament-like overall shapes. Superclusters can be divided into two sets; more elongated superclusters are more luminous, richer, have larger diameters, and a more complex fine structure than less elongated superclusters. The fine structure of superclusters can be divided into four main morphological types: spiders, multispiders, filaments, and multibranching filaments. We present the 2D and 3D distribution of galaxies and rich groups, the fourth Minkowski functional, and the morphological signature for all superclusters. Widely different morphologies of superclusters show that their evolution has been dissimilar. A study of a larger sample of superclusters from observations and simulations is needed to understand the morphological variety of superclusters and the possible connection between the morphology of superclusters and their large-scale environment.Comment: Comments: 20 pages, 18 figures, accepted for publication in Astronomy and Astrophysic

Rotation Measures of Radio Sources in Hot Galaxy Clusters

The goal of this work is to investigate the Faraday rotation measure (RM) of radio galaxies in hot galaxy clusters in order to establish a possible connection between the magnetic field strength and the gas temperature of the intracluster medium. We performed Very Large Array observations at 3.6 cm and 6 cm of two radio galaxies located in A401 and Ophiuchus, a radio galaxy in A2142, and a radio galaxy located in the background of A2065. All these galaxy clusters are characterized by high temperatures. We obtained detailed RM images at an angular resolution of 3'' for most of the observed radio galaxies. The RM images are patchy and reveal fine substructures of a few kpc in size. Under the assumption that the radio galaxies themselves have no effect on the measured RMs, these structures indicate that the intracluster magnetic fields fluctuate down to such small scales. These new data are compared with RM information present in the literature for cooler galaxy clusters. For a fixed projected distance from the cluster center, clusters with higher temperature show a higher dispersion of the RM distributions (sigmaRM), mostly because of the higher gas density in these clusters. Although the previously known relation between the clusters X-ray surface brightness (Sx) at the radio galaxy location and sigmaRM is confirmed, a possible connection between the sigmaRM-Sx relation and the cluster temperature, if present, is very weak. Therefore, in view of the current data, it is impossible to establish a strict link between the magnetic field strength and the gas temperature of the intracluster medium.Comment: Accepted by Astronomy and Astrophysics, 26 pages, 19 figure

Post neutron irradiation annealing and defect evolution in single crystal tungsten

Single crystal W is offered for Physics understanding of irradiation induced defects and their annealing as its structure is well defined and it is almost defect free. W(100) single crystal was neutron irradiated to a damage of 0.11 displacements per atom at 600 °C and subsequently isochronally annealed from 700 up to 1500 °C in 100 °C steps. Irradiation causes the formation of dislocation loops and vacancy clusters and a 45 % increase in hardness. After the annealing of 1500 °C the positron lifetime annihilation spectrum shows a defect free material and its hardness has been reverted to the pre-irradiation value and only clusters of Re, WRe and WOs2 have been detected by grazing incidence X-ray diffraction. The total line density of dislocations, number density of voids and their size versus annealing temperature have been determined. From hardness, the critical resolved stresses arising from dislocations and voids have been derived and correlated with their densities. The kinetics of defect annihilation versus annealing temperature is discussed

Neutron irradiation effects in different tungsten microstructures

In this work the correlation of the neutron radiation damage and tungsten (W) microstructure is investigated. Further, the modification of the structure as a result of the neutron irradiation is assessed and its effect on the mechanical properties is determined. Forged bar (ITER grade), cold rolled sheet, and single crystalline tungsten materials were neutron irradiated at 600 °C to a damage of 0.12 displacements per atom. Neutron irradiation results in the formation of voids of almost the same size (larger than 1 nm) and dislocations detected by positron annihilation lifetime spectroscopy. All W grades have similar total dislocation densities, in the range of (1.6-2.4)×1014 m-2, as determined by electrical resistivity measurements. After irradiation the hardness of all tungsten grades increases and the largest increase is that of the single crystal (47%), whereas the smallest that of the sheet (13%). Increase in the yield strength, correlated to the increase of the hardness, is also found. The largest increase is observed for the single crystal (25%) and the smallest for the sheet (6%). The different degrees of hardening and strengthening indicate that the microstructure of the different tungsten grades has a significant influence on their neutron radiation damage resistance. © 2021 IOP Publishing Ltd

The competing effects of temperature and neutron irradiation on the microstructure and mechanical properties of ITER grade tungsten

In the current work, ITER grade W irradiated at 1200 oC to a dose of 0.18 dpa has been investigated by Transmission Electron Microscopy (TEM), Positron Annihilation Spectroscopy (PAS), X-ray diffraction, impulse excitation and depth-sensing micro-indentation. The results are compared with those of annealed unirradiated W at 1200 oC. In the as fabricated material dislocations and small vacancy clusters of 1 to 3 vacancies are present. After annealing at 1200 oC, the small vacancy clusters disappear and only the dislocations with almost unchanged density remain. Also, hardness is reduced by 4% and creep increases by 13%. Neutron irradiation at 1200 °C results in the increase of the dislocation line density by 3.7 times and in the formation of dislocation loops and voids. The irradiation also causes a hardness increase of about 20% and a creep decrease of 15%. Both the elastic and shear moduli decrease by 4% after irradiation at 1200 °C contrary to the effect of only annealing at this temperature which causes an increase in their values by 4%. Texture changes are observed only after neutron irradiation. © 202

Evolution of microstructure in neutron irradiated cold rolled tungsten and its correlation with hardness

The understanding of the neutron irradiation effects in tungsten is of significant importance for its use as a plasma facing material in future fusion devices. In this study, cold rolled tungsten is neutron irradiated at the Belgian BR2 fission reactor at the temperatures 600, 800, 900 and 1200 °C to a dose of 0.18 displacements per atom (dpa). The neutron induced changes in the microstructure are investigated as a function of irradiation temperature using transmission electron microscopy, positron annihilation spectroscopy and electrical resistivity measurements. The influence of the irradiation on the elastic properties and the hardness is examined using the impulse excitation techniques and depth-sensing indentation. Voids and dislocation loops are observed at all the irradiation temperatures. As the irradiation temperature increases the number density of both voids and loops decreases whereas their size increases. The total dislocation density increases after irradiation at 600 °C whereas it decreases for higher temperature irradiations. Furthermore, the formation of very small vacancy clusters in the temperature range of 800 - 900 °C is revealed by PAS measurements. A systematic decrease in the values of Young's and shear moduli is observed as the irradiation temperature increases and this decrease is of about 3.5% after irradiation at 1200 °C. A considerable hardening effect is observed at all irradiation temperatures. The hardness increases with irradiation temperature reaching a maximum at 800 °C and remains almost constant at higher irradiation temperatures. © 2021 Elsevier B.V

The competing effects of temperature and neutron irradiation on the microstructure and mechanical properties of ITER grade tungsten

In the current work, ITER grade W irradiated at 1200 degrees C to a dose of 0.18 dpa has been investigated by Transmission Electron Microscopy (TEM), Positron Annihilation Spectroscopy (PAS), X-ray diffraction, impulse excitation and depth-sensing micro-indentation. The results are compared with those of annealed un-irradiated W at 1200 degrees C. In the as fabricated material dislocations and small vacancy clusters of 1 to 3 vacancies are present. After annealing at 1200 degrees C, the small vacancy clusters disappear and only the dislocations with almost unchanged density remain. Also, hardness is reduced by 4% and creep increases by 13%. Neutron irradiation at 1200 degrees C results in the increase of the dislocation line density by 3.7 times and in the formation of dislocation loops and voids. The irradiation also causes a hardness increase of about 20% and a creep decrease of 15%. Both the elastic and shear moduli decrease by 4% after irradiation at 1200 degrees C contrary to the effect of only annealing at this temperature which causes an increase in their values by 4%. Texture changes are observed only after neutron irradiation