arXiv subjects

Yury Petrov

Publications and source records attributed to Yury Petrov.

3 recordsLinked to original sources

arXiv2023

Shock-induced melting and crystallization in titanium irradiated by ultrashort laser pulse

Modification of titanium microstructure after propagation of a melting shock wave (SW) generated by a femtosecond laser pulse is investigated experimentally and analyzed using hydrodynamic and atomistic simulations. Scanning and transmission electron microscopy with analysis of microdiffraction is used to determine the microstructure of subsurface layers of pure titanium sample before and after modification. We found that two layers of modified titanium are formed beneath the surface. A top surface polycrystalline layer of nanoscale grains is formed from a shock-molten layer via rapid crystallization. In a deeper subsurface layer, where the shock-induced melting becomes impossible due attenuation of SW, recrystallization of plastically deformed titanium leads to grain size changes in comparison with intact titanium. Molecular dynamics simulation of single-crystal titanium reveals that the SW front continues to melt/liquefy even after its temperature drops below the melting curve $T_m(P)$. The enormous shear stress generated in a narrow SW front leads to collapse/amorphization of the crystal lattice and formation of a supercooled metastable melt. Such melt crystallizes in an unloading tail of SW until its temperature becomes higher than $T_m(P)$ due to a rapid pressure drop. Later, crystallization of the subsurface molten layer will continue after the heat leaves it. After the shear stress drops below $\sim 12$GPa within the SW front, such the cold mechanical melting ceases giving place to the shock-induced plastic deformations. The depth of modification is limited by SW attenuation to the Hugoniot elastic limit, and can reach several micrometers. The obtained results reveal the basic physical mechanisms of surface hardening of metals by ultrashort laser pulses.

physics.flu-dyn↗

arXiv2004

Study of plasma heating in ohmically and auxiliary heated regimes in spherical tokamak Globus-M

The ion temperature behavior in the plasma core of the spherical tokamak Globus-M (major radius 0.36 m, minor radius 0.24 m, torus aspect ratio 1.5, toroidal magnetic field near the plasma axis 0.4 T, plasma current up to 0.3 MA) was studied by means of 12-channels neutral particle analyzer (NPA) ACORD-12. The experiments were performed in ohmic regimes as well as in regimes with the ion cyclotron resonance heating (ICRH) in the vicinity of fundamental harmonic for hydrogen minority in deuterium bulk plasma and the neutral beam injection (NBI). The total auxiliary power exceeded the magnitude of 0.8-1 MW. The NPA provided the simultaneous measurements of deuterium and hydrogen energy spectra and the percentage of both isotopes. The ion temperature was studied in a wide range of the plasma current 0.08-0.3 MA and the plasma average density (1-7)x1019 m-3 at various values of the plasma vertical elongation and the triangularity. The experimental data were compared with the results of numerical simulation. We employed a simple 1D model describing the ion energy balance by using the neoclassical transport coefficients. The charge-exchange losses were also taken into account. The experimentally measured ion temperature dependence on the plasma current and plasma density differed from the Artsimovich scaling law predictions well describing the ion heating in the case of the neoclassical plateau regime in the conventional tokamak even at a relatively low temperature in ohmic plasma. In particular strong, almost linear plasma current temperature dependence was revealed. It indicates a dominating role of trapped particles in the ion energy balance at a low aspect ratio. The estimates of energy confinement time values derived from the magnetic measurements in ohmic and auxiliary heating regimes are also presented.

physics.plasm-ph↗

arXiv2000

Phonon mediated hole pairing in the 1D Hubbard model near half-filling

The Hamiltonian describing a system of strongly correlated electrons coupled to dispersionless phonons was solved numerically for a ring of 8 atoms using the density matrix renormalization group (DMRG) method. It was found that electron correlation and electron-phonon coupling compete against each other, and strong electron correlations suppress the charge-ordered insulating state. This allows extended polarons to form in the strong electron-phonon coupling regime. It is shown that in this regime two polarons may form a pair via phonon mediated charge-fluctuation interaction. Based on the results we propose a novel mechanism of hole pairing. This mechanism could be relevant to High-Tc cuprates.

cond-mat.str-el↗