arXiv subjects

N. V. Sakharov

Publications and source records attributed to N. V. Sakharov.

3 recordsLinked to original sources

arXiv2026

Low-temperature Spark Plasma Sintering of fine refractory composite powders core-shell: A case of the powders W@Ni

The mechanisms of fast low-temperature Spark Plasma Sintering (SPS) of W + 10% wt. Ni powders were investigated. The powder compositions were obtained in two methods: (i) by mixing W and Ni powders in a specified ratio (hereinafter referred to as W + Ni); (ii) by Ni deposition on the surface of submicron W particles allowing the formation of particles with a core W - shell Ni structure (hereinafter referred to as W@Ni). To reduce the concentrations of oxygen and oxides, the powders were annealed in hydrogen. The solid-phase sintering was performed at various temperatures (1000-1150°C), pressures (40-80 MPa), heating rates (50-500°C/min), and isothermal holding times (0-20 min). The sintering temperatures corresponded to the onset of intense dissolution of W in Ni. The samples had high relative density and small grain sizes. The activation energy of SPS of the mixed powders was close to the one of the grain boundary diffusion. The key mechanism for the compaction of W@Ni particles in the SPS process is Coble creep. The increasing of the sintering temperature was shown to lead to an increase in the solubility of W in Ni and, consequently, to an increase in the number of secondary Ni4W particles formed during cooling down. The grain growth has a minor effect on the mechanical properties of the W alloy compared to the changes in its phase composition.

cond-mat.mtrl-sci↗

arXiv2025

Hot-Ion Modes in Globus-M2 and Saturation of Energy Confinement Time Scaling in Spherical Tokamaks with Toroidal Magnetic Field of 1 T and Above

In a small spherical tokamak with minor radius of 0.22 m and toroidal magnetic field of 1 T, it is possible to heat ions of a sufficiently dense plasma to an extremely high temperature up to 50 million Kelvin. To do this, it is necessary to transfer a sufficiently large torque to stabilize ion-scale turbulence and achieve ion heat transport at neoclassical level reaching extremely low values of plasma collisionality. It is also necessary to ensure good thermal insulation of electrons, which is always determined by turbulent transport. In a spherical tokamak, the toroidal magnetic field has a strong beneficial effect on suppressing turbulent electron heat fluxes. In the Globus-M2 tokamak, when heating plasma with high-energy atomic beams, a significant improvement in the plasma thermal energy confinement is observed with an increase in the toroidal magnetic field from 0.5 to 1 T. The comparison of our results with experiments on ST40 tokamak operating with toroidal magnetic field of 2 T indicates that further strong improvement of thermal insulation of spherical tokamak plasma in the region of higher magnetic fields is not expected.

physics.plasm-ph↗

arXiv2022

Investigation of the microstructure of the fine-grained YPO$_4$:Gd ceramics with xenotime structure after Xe irradiation

The paper reports on the preparation of xenotime-structured ceramics by the Spark Plasma Sintering (SPS) method. Phosphates Y$_{0.95}$Gd$_{0.05}$PO$_4$ (YPO$_4$:Gd) were obtained by the sol-gel method. The synthesized nanopowders are collected in large agglomerates 10-50 mkm in size. Ceramics has a fine-grained microstructure and a high relative density (98.67%). The total time of the SPS process was approximately 18 min. High-density sintered ceramics YPO$_4$:Gd with a xenotime structure were irradiated with Xe$^{+26}$ ions (E = 167 MeV) to fluences of $1\times10^{12}$-$3\times 10^{13}$ cm$^{-2}$. Complete amorphization at maximum fluence was not achieved. As the fluence increases, an insignificant increase in the depth of the amorphous layer is observed. According to the results of grazing incidence XRD (GIXRD), with an increase in fluence from $1\times10^{12}$-$3\times 10^{13}$ cm$^{-2}$, an increase in the volume fraction of the amorphous structure from 20 to 70% is observed. The intensity of XRD peak 200 YPO$_4$:Gd after recovery annealing (700$^\circ$C, 18 h) reached a value of ~80% of the initial intensity I0.

cond-mat.mtrl-sci↗