Synthesis and Magnetic Properties of Iron Polyhydrides at Megabar Pressures

JETP Letters - Iron polyhydrides have been synthesized at pressures of 77–157 GPa and temperatures up to 2000 K by the laser heating of an iron–borazane (ammonia borane NH3BH3) sample...     

Erratum to: Synthesis and Magnetic Properties of Iron Polyhydrides at Megabar Pressures

JETP Letters - An Erratum to this paper has been published: https://doi.org/10.1134/S0021364023330019     

The Electric Explosion of Conductors in Megagauss Magnetic Fields

The results are presented from an experimental study of the explosion of copper conductors performed at ~2 MA current pulse with a rise time of 100 ns using the MIG generator. Using a HSFC Pro optical camera, large-scale instabilities with wavelengths of 0.2–0.5 mm are recorded on the surface of the conductor. The instabilities are tongue-shaped ejections of plasma expanding at the speed of sound in the direction opposite the gradient of the magnetic field. The obtained data are analyzed using two-dimensional magnetohydrodynamic simulation. It is shown the emergence of the observed structure was likely due to the growth of flute instabilities.     

Experimental Study of Ion-Acoustic Instability in Stratified Krypton and Xenon Plasma at High Pressures

The ion-acoustic instability in gaseous discharge plasma in krypton and xenon at the pressures 0.4 to 2.5 Torr was found and studied. The necessary conditions for the instability existence were satisfied only in the ionisation wave region where electron density was about an order larger than average one. The detected noise amplitude and frequency dependence on the glow discharge plasma parameters was also investigated.     

Quasi-Isentropic Compression of a Nonideal Plasma of Deuterium and its Mixture with Helium at Pressures up to 250 GPa

Journal of Experimental and Theoretical Physics - We present data on the quasi-isentropic compressibility of a strongly coupled (nonideal) plasma of a deuterium–helium mixture in the range of...     

Transport Properties for a Collisionless Plasma from Finite-Larmor-Radius Equations in General Magnetic Fields

We have take the Vlasov equation in a local system of coordinates defined by the curved magnetic field and we have expanded the distribution function in terms of a small parameter ? which is the ratio of ion Larmor radius to the characteristic length in the direction perpendicular to magnetic field. Assuming an approximation for the distribution function, which is consistent with physical systems, we have obtained transport properties in different orders of approximation taking account of the general heat flux vector. We find that there are additional terms appearing in the components of stresses due to the parallel energy flow term in the heat flux vector.     

Plasma Oscillations and Their Influence on Certain Properties of Nonideal Plasma

The hypothesis is proposed that Langmuir plasma oscillations can exist in nonideal plasma inspite of great collisional frequency. This possibility is confirmed by numerical estimations and the results of several experiments. The influence of plasma oscillations on electron states density and conductivity of nonideal plasma is considered. The simple formula obtained for conductivity agrees well with available experimental data.     

Nonlinear Effects of a Gaussian Laser Beam on Megagauss Magnetic Field Generation in Laser Produced Plasma

The generation of megagauss magnetic field due to the time dependent part of the ponderomotive force of a self-focused Gaussian laser beam indicent on a plasma has been studied. Defocusing of the laser beam becomes possible due to diffraction divergence in the case of a weakly nonlinear medium. The influence of defocusing of a laser beam on magnetic field generation has also been investigated. It is found that the magnitude of the magnetic field due to self focusing of the beam is enhanced and is comparable with the observed values, while there is a reduction in the magnitude of the magnetic field when the beam defocuses due to diffraction divergence in the presence of weak nonlinearity.     

Use of Pulsed Radiography for Investigation of Equations of State of Substances at Megabar Pressures

A method of density measurement for substances that are isentropically compressed up to megabar pressures is described in the paper. Measurement results for condensed hydrogen isotopes and aluminum are presented. These results, afterwards, are used for construction of hydrogen isotopes “cold” isentropes. Experimental x‐ray images of the facilities with the hydrogen isotopes, compressed up to several megabars are presented in the paper (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetic Properties and Spin Crossover in Transition Metal Oxides with d 5 Ions at High Pressures

We analyze the influence of cooperative effects on the magnetic properties and spin crossover between the high-spin (HS) term S = 5/2 and low-spin (LS) term S = 1/2 in Mott–Hubbard dielectrics with 3d5 ions under high pressures. Two cooperation mechanisms (superexchange interaction and effective interaction via the elastic system) are considered. The sign of the exchange interaction changes because of the crossover from the antiferromagnetic in the HS state to the ferromagnetic in the LS state. In view of the large difference between the ionic radii of the HS and LS states, the systems with spin crossover acquire an additional strong coupling via the elastic system. Using the Hubbard operator representation and considering the electronic states of the two terms simultaneously, we obtain the effective Hamiltonian with allowance for the cooperative effects. The magnetic phase diagram and the spin crossover are investigated in the mean field approximation. It is shown that the inclusion of cooperative effects at low temperatures leads to a first-order phase transition between the antiferromagnetic HS state and the ferromagnetic LS state. At higher temperatures, more complicated sequences of phase transitions are possible upon an increase in pressure, including the HS paramagnet–HS antiferromagnet–LS paramagnet and HS antiferromagnet–LS paramagnet–LS ferromagnet transitions.     

Screening Breakdown in a Plasma by Two Laser Fields and Strong DC Magnetic Field

The effective static dielectric constant of an electron plasma system in the simultaneous presence of two electromagnetic waves and a strong DC magnetic field is calculated. It is found that as the difference Δω of the two electromagnetic wave frequencies matches the plasma frequency ω_ρ a breakdown in screening occurs thereby increasing the plasma heating rate via the external fields due to inverse Bremmstrahlung. An application is made by considering the typical parameters of a hot plasma. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrons in a Nonideal Partially Degenerated Plasma with Multiple Ionization

We consider peculiarities in the behavior of free electrons in an extremely-dense hot plasma with multiple ionization and partial degeneration. In different ways, we exhibit the strong Coulomb coupling of electrons and ions in the behavior of low- and high-kinetic-energy electrons. As a result, a necessity arises to consider, along with classical fast Debye electrons, their complementary cellular group of electrons constantly interacting with central ions of cells. We discuss the distribution of free electrons between the two groups, along with the role of two-group effects, of a not point character of ions in electron-transfer processes, and the consequences of the X-ray emitting X-pinch hot spot for the plasma. The existence of the physical limits for X-pinch plasma compression is among those consequences.     

Effect of Longitudinal Magnetic Field on the Spread of Erosion Laser Plasma in Vacuum and Generation of Plasma Magnetic Fields

Dynamics of erosion laser plasma in vacuum and generation of magnetic field by moving plasma (in particular, in the presence of external static magnetic field oriented along the direction of plasma motion) are experimentally studied. Radial confinement of the spread of plasma, a decrease in the electrification of target upon plasma formation, and an increase in the induction of the plasma magnetic field by a factor of 10–15 are revealed at an induction of the external magnetic field of about 0.35 T. Dependences of the induction of the plasma magnetic field on the power density of the laser radiation are determined for the above regimes.     

New Results in the Field of a Nonideal Plasma. Experiments and Interpretation

Experiments on the electronic transport, thermodynamic and optical properties of the dense metal vapors are briefly discussed. Interpretation based on the cluster ions and percolation clusters theory is given.     

Modeling the Properties of Helium at High Pressures

The paper presents simulation of shock-wave compression of liquid helium. Considering the possible ionization at high compression rates is shown to increase the accuracy of prediction of the helium properties.     

Thermomagnetic effect in a Knudsen gas at low temperatures

The thermomagnetic effect (TME) in nitrogen interacting with a gold surface is investigated. It has been found that at temperatures T<100K the sign of the effect and the dependence of the heat flux on the magnitude and direction of the field do change.     

Optical Properties of Doped Nanowires in External Electric and Magnetic Fields

Optics and Spectroscopy - Impurity-induced absorption of light in quantum wires in the presence of external collinear electric and magnetic fields directed perpendicular to the nanowire axis is...     

Erratum to: Magnetic Properties and Spin Crossover in Transition Metal Oxides with d5 Ions at High Pressures

Journal of Experimental and Theoretical Physics - erratum