Vol 63, No 7 (2018)

The nonlinear Langevin equation for a system of Coulomb particles with random processes, which are functionals of the velocity distribution function of such particles, has been derived and analyzed. It is shown by direct numerical solutions that this equation correctly describes the collisional relaxation of such a system even in the case of anomalous deviation of the initial velocity distribution of particles from the equilibrium distribution. The equation can be conveniently used in the Monte Carlo methods and in “particle-in-cell” methods.

The necessity of choosing multiparametric wavefunctions for describing the ground state of an atom in the problems of ionization of atoms by photons and electrons has been substantiated for the He atom as an example. Comparative analysis of application of different ground-state wavefunctions for this atom has been performed. The energies, widths, and partial widths of the lower autoionization state ¹P of the He atom above the excited ion formation threshold has been performed. It is shown that in contrast to total widths of quasi-stationary states, which differ insignificantly for different wavefunctions of the ground state, the partial widths are substantially different.

The results of experimental investigation of critical flow of liquid nitrogen in a long adiabatic channel are presented. As the experimental specimen a channel with a length of 1646 mm, and an inner diameter of 4 mm was used. Pressure in the experiments at the inlet to the specimen was changed in the range p_in = (3.06–5.39) × 10⁵ Pa, the outlet pressure was p_out = (1.26–4.44) × 10⁵ Pa, and the volumetric flow rate was in the range V = (0–0.042) × 10^–3 m³/s. The calculation of the coordinate of the cross section, in which one should expect the emergence of a shock wave, has been conducted. The calculation of local values of speed of sound and the velocity of the mixture allowed us to determine the critical value of the volumetric vapor quality in the critical cross section. Quantitative comparison of the conditions of emergence and existence of the critical flow in the long channel in comparison with short channels is carried out. Fundamental differences are shown.

The results of experimental studies of the influence of runaway electrons on the parameters of the neutral gas breakdown and suppression of the runaway electron flow in the Uragan-2M torsatron are presented. The influence of the presence or absence of the runaway electron flow on the time characteristics of the breakdown is experimentally studied via comparative analysis. It is demonstrated that in the presence of the runaway electron flow the breakdown takes place earlier by an average of 1.5 ms, as compared to the breakdown in the absence of the runaway electron flow. This is also proved by the earlier results obtained at the Uragan-3M torsatron, which allows one to continue the description of some aspects of the runaway electron dynamics and its regularities and formulate a number of recommendations on controlling such electron flows in fusion installations.

Experimental data on electrical breakdown of air in a linearly polarized traveling microwave with a deeply subcritical field are presented. Breakdown is initiated by a linear electromagnetic vibrator or a set of vibrators. They are placed over a metal surface the plane of which contains the wavevector of the microwave and its electrical component. The axes of the vibrators are parallel to this component, and their distances to the metal surface are shorter than the quarter-wavelength of the field. In experiments with the single vibrator, this distance is varied. When the set of vibrators is used, they were placed one after another along the wavevector of the field.

We have analyzed the equilibrium configuration of a pile-up of edge dislocations in the total field of external and internal elastic stresses produced by a wedge junction disclination. The conditions for the loss of pile-up stability and the passage of a plastic shear through the force barrier generated by the disclination have been analyzed.

The results of the investigation of physicomechanical properties of the material produced from polylactide with the topology of triply periodic minimal surfaces have been presented. The samples were obtained in the form of a cube, which consisted of repeating elements with the minimum possible area, by the fused deposition method on an FDM 3D printer. When comparing the experimental deformation curves, it has been found that the obtained curves qualitatively differ from each other under loading at different direction with respect to the construction axis of the product, since the same material behaves as both fragile and plastic. A difference in magnitude of the specific yield limit (σ_sp, MPa сm³/g) was established depending on the load direction: 7.6, if it is perpendicular to the construction axis; 11.3, if it is along the construction axis; 27.6, if it is along the construction axis with plates on two sides. The performed work is preparatory in order to develop periodic structures based on ceramics, which can be used as protective layers of equipment.

The conditions of synthesis of antimony/carbon composites by interlayer self-assembly from colloidal solutions and melts are discussed. The morphology and the structure of these composites are examined. The potential to produce composites of 2D and 3D morphologies is demonstrated. The 2D composite has a multilayer graphene structure with submicron antimony inclusions, while the 3D composite has a spheroidal shell structure with a deformed film-shell with carbon nanoinclusions. The difference in properties of these composites is demonstrated: the 2D composite is conductive, while the 3D composite has a nonlinear current–voltage characteristic that indicates the emergence of novel functional properties of the spheroidal antimony/carbon composite. A model of exfoliation of the layered precursor with covalent interlayer coupling is proposed. This model provides an explanation for the experimentally observed nonlinear hydrodynamic processes in the colloidal antimony solution.

The absorption spectra of C₆₀ fullerene thin (from submonolayer to 5–6 monolayers) films deposited on different substrates have been studied. It has been shown that the spectra of the submonolayer and thick (more than 100 monolayers) films virtually coincide. The behavior of fullerene on the surface of different polymers can be judged from changes in the absorption spectra.

Tamm surface states are experimentally studied and calculated for a Bragg heterostructure consisting of two groups of periodic fragments of waveguide slot transmission line with finite sizes. The Tamm surface states are not observed in a perfect Bragg heterostructure. The Tamm surface states emerge in the presence of an interface element at the interface of two Bragg structures when the characteristics of the element differ from the characteristics of both Bragg structures.

The use of surface active liquids facilitates intense stratification of mechanically strained Bi_0.5Sb_1.5Te₃ crystallites. A Bi_0.5Sb_1.5Te₃ heat element with specified thickness and structure is formed by layer-by-layer deposition of “thermoelectric ink” on its free surface. A heat treatment of the formed thermoelectric element in argon at a temperature of 800 K makes it possible to minimize radically the resistance of the grain boundaries introduced into its bulk.

A series of equidistant oscillations have been revealed in the transmission spectrum and dispersion law of Damon–Eshbach surface magnetostatic waves (SMSWs) propagating in submicron (200-nm) yttrium–iron garnet (YIG) films manufactured by means of ion-beam sputtering onto gadolinium–gallium garnet (GGG) substrates. These oscillations correspond to the excitation of magnetoelastic waves in the YIG–GGG structure at frequencies of resonant interaction between the surface magnetostatic waves and the elastic shear modes of the wave-guiding YIG–GGG structure. The obtained results show that the studied YIG films are characterized by an efficient magnetoelastic coupling between their spin and elastic subsystems and the matching of acoustic impedances at the YIG–GGG interface, thus providing the possibility to consider the ion-beam sputtering of YIG films onto GGG substrates as a promising technology for the creation of magnonic and straintronic devices.

Monochromators based on a noncollinear acousto-optic filter without external polarizers have been studied. As an element to select an operating diffracted light beam, (1) a spatial filter-telescope and (2) an output plane of a filter crystal rotated in a diffraction plane have been used. In the latter case, dispersion of the acousto-optic filter crystal is compensated using a correcting prism made from the same crystal and placed behind an output filter plane along a path of a filtered light beam. As a result, the transmission coefficient of the monochromator is increased upon an effective compensation of the angular drift of the filtered light beam, the monochromator design is simplified, and its sizes are decreased.

Nanocomposite painting and varnishing materials on the basis of carbon nanomaterials and organic polymers can be used to create microwave protective coatings. Such coatings show thermo-, chemo-, plasma-, and radiation-resistant properties. Largely, these properties are determined by the concentration of carbon nanomaterials in composites. Moreover, different nanomaterials in such coatings show fundamentally different concentration dependences of the electrical conductivity.

Molecules of diphenylphthalide and 3,3-diphenylphthalide-4′,4′-dicarbonic acid have been studied using the method of dissociative electron capture negative ion mass spectrometry. The mean lifetimes of negative molecular ions relative to the electron detachment have been measured. The electron affinity has been estimated in the Arrhenius approximation and calculated by the DFT B3LYP/6-31G+(d) method.

We propose and study numerically a large-aperture electrostatic spectrograph consisting of the two coaxial electrodes, a cone-cylindrical electrode separated into several segments, and a small cylindrical electrode. The supply voltages providing sharp focusing of charged particle beams in the initial region of the spectrum for different ranges of simultaneously detected energies E_max/E_min = (25–100) are determined. Electron- optical parameters of the spectrograph in four energy ranges are calculated, with the electrical similarity principle being used for charged particles of medium and high energies. The resolution of the spectrograph for medium and high energies, E = (0.1–1)E_max, is equal to (5–3) × 10^–3. For small energies, E = (0.01–0.1)E_max, the resolution worsens and varies within the (0.6–1.6) × 10^–2 range as the range of simultaneously recorded energies increases.

We consider the effect of the multiple Coulomb scattering on the spatial dynamics of the relativistic hose instability of a relativistic electron beam propagating along an Ohmic plasma channel. It is shown that the enhancement of scattering noticeably suppresses this instability.

X-ray diffraction data and X-ray fluorescence analysis data for microchannel plates are presented. From X-ray diffraction patterns, one can estimate the amount of reduced lead in microchannel plates and make sure of the presence of both metallic lead and semiconducting PbO_x with a variable oxygen content.

A technique for precision rapid nondestructive monitoring of the dopant behavior in zinc chalcogenide–based laser media is reported. Results suggest that it is possible to determine the concentration profiles of Fe²⁺ and Cr²⁺ dopant ions in zinc chalcogenide by IR spectroscopy combined with an IR microscope in the concentration rage 5 × 10¹⁷–2.5 × 10²⁰ atoms/cm³ with a spatial resolution of several micrometers. The diffusion profiles of dopants have been taken for zinc chalcogenide codoped by several impurities.