Bulletin of the Russian Academy of Sciences: Physics最新文献

We present the results of probe measurements of plasma parameters and ion mass-to-charge state of a DC magnetron sputtering system (MSS) in gas and vacuum (gasless) operating modes at operating pressures from 2 down to 0.05 mTorr. It is shown that, in comparison with the gas operating mode, the discharge plasma of the vacuum magnetron is characterized by higher values of electron temperature and plasma potential, along with the generation of multiply charged metal ions of the target material. This mode is also characterized by a higher degree of ionization of sputtered material and enhanced ion current density onto the substrate. The revealed differences may be useful for improving quality and properties of formed coatings.

The work is devoted to the study of the structure of plasma jets formed by a high-current vacuum arc discharge. The experiments were conducted on the high-current generator IMRI-5 with a current amplitude of 250 KA. The plasma jet was formed while burning a vacuum arc discharge between coaxial aluminum electrodes with initiation on the surface of a capropolon dielectric. The following were registered in the experiments: a current flowing along the plasma jet at different distances from the plasma gun cathode; visible image of a plasma jet at different moments in time with an exposure of 10 ns; the propagation speed of the plasma jet. Numerical simulation of the evolution of the plasma jet was carried out. The results of the simulation are compared with the experiments.

High-entropy borides (HEB) are a new class of unique materials characterized by outstanding properties. In this paper, a comprehensive study of the oxidation properties of a high-entropy boride of the composition (Ti_0.2Zr_0.2Nb_0.2Hf_0.2Ta_0.2)B₂ is carried out for the first time. HEB was synthesized by a vacuum-free electric arc method by a direct current arc discharge of 100 A for 90 s. The oxidation stability of the obtained powder (Ti_0.2Zr_0.2Nb_0.2Hf_0.2Ta_0.2)B₂ was studied by two approaches. In the first case, it was found that the (Ti_0.2Zr_0.2Nb_0.2Hf_0.2Ta_0.2)B₂ sample is characterized by an oxidation temperature of ~800°С based on the assessment of phase transformations in situ during heating of the powder in the temperature range from 0 to 1200°С in air. In the second case, it was determined that the (Ti_0.2Zr_0.2Nb_0.2Hf_0.2Ta_0.2)B₂ powder can withstand temperatures up to ~700°С according to the results of the analysis of the composition of HEB during oxidation in an atmospheric furnace. The formation of oxides is confirmed by the results of scanning electron microscopy. The characteristics of HEB obtained in the work are consistent with the currently known literature data.

A mathematical model is developed that describes the process of the initial stage of electrical explosion of cylindrical conductors in the skin current mode. The model describes: nonlinear diffusion of the magnetic field; Joule heating; dynamics of the conducting material under the action of the Ampere force and thermoelastic stresses; phase transitions “solid–liquid” (melting) and “liquid–vapor” (evaporation). The influence of a non-uniform initial spatial profile of specific electrical resistance ({{rho }_{e}}(r)) near the conductor surface on the processes under study is analyzed. Profiles ({{rho }_{e}}(r)) with different abruptness of transition from surface to volume values, and with different effective thickness of the modified layer are considered. The possibility of delaying plasma formation on the surface due to the use of initial profiles ({{rho }_{e}}(r)) with increased values of specific resistance on the surface is discovered.

One of the trigger systems for the pseudospark switches is based on a usage of the low-current auxiliary glow discharge with hollow cathode and hollow anode. The electrodes of the auxiliary discharge are often placed inside the grounded cathode cavity of the main high-voltage electrode gap. The space of the auxiliary discharge communicates with the space of the main cathode cavity via the aperture in the flat part of one of the trigger electrodes. Then the characteristic feature of such an arrangement is the availability of the so-called parasitic current, which flows via the aperture to the grounded cathode. This paper deals with the investigation of the features of the formation of the parasitic current at different electric circuits for powering the auxiliary discharge.

We investigated the effect of the beam plasma parameters on the modification of the polypropylene surface properties in argon and air atmospheres. This beam plasma was generated by a ribbon electron beam at a pressure of 0.1–10 Pa. The results show a non-monotonic increase in plasma concentration (up to 3 × 10¹⁵ m^–3) at a pressure of 1 Pa for argon plasma. This increase might be associated with the ignition of a beam-plasma discharge. However, this dependence of plasma parameters on pressure is monotonous for air plasma. The study shows that air plasma treatment provides a more pronounced reduction in the wetting edge angle compared to argon plasma. This decrease might be explained by the combined physical and chemical effects of the air active components. The use of electric potential had made it possible to enhance surface modification, especially at low pressures. The highest processing efficiency was achieved in the 1–5 Pa range, where an optimal balance is maintained between plasma density and particle energy. In addition, the air plasma ensures a longer retention of hydrophilic properties compared to argon plasma treatment. The obtained results can be important for the processing polymer materials technologies development.

We studied the dynamics of a microsphere with a double-layer shell embedded in a polymeric matrix under the impact of a shock wave. Deformation and destruction mechanisms of the microsphere’s shell are considered, as well as the influence of the polymer matrix properties on the transmission of shock loads. In the first part of the study, using computer models, a series of numerical experiments was conducted to analyze processes of shock wave propagation through the composite material, considering differences in mechanical properties between the shell layers and the polymer medium. It was shown that the double-layered shell structure promotes effective absorption of the impact energy and formation of fibrous structures. In the second stage of the research, modeling of the stress–strain state of the heterogeneous material under the influence of a relativistic electron beam (REB) was carried out. For this purpose, a procedure for averaging the physical and mechanical properties of the composite components was implemented, allowing an accurate description of the material response to high-energy external loading. The obtained results demonstrate the promise of applying numerical averaging methods for predicting the behavior of heterogeneous materials under extreme conditions. The results of this work can be used for optimizing the properties of composite materials employed under dynamic load conditions such as shock waves and exposure to intense charged particle beams.

The safe treatment and reliable immobilization of waste generated during the reprocessing of spent nuclear fuel remain critical challenges for nuclear power. This study evaluates the feasibility of a plasma-based route that converts liquid reprocessing residues into chemically stable metal-oxide powders and then immobilizes these products into durable matrices suitable for long-term storage. The approach combines thermodynamic modeling with laboratory-scale experiments. Modeling was used to determine adiabatic combustion temperatures and equilibrium phase compositions for water–salt–organic feeds under plasma exposure. Experiments with a high-frequency plasma generator confirmed that, under optimized conditions near 1200°C, organic constituents are completely oxidized, and finely dispersed oxides are formed. The resulting powders include simple and complex oxides of iron, molybdenum, zirconium, neodymium, cerium, strontium, and yttrium; the phase balance depends on the plasma-cooling regime. Post-processing by gravitational and magnetic separation improves powder recovery and purity. For final conditioning, the oxides were incorporated into chloride-based melts, yielding dense, chemically and thermally stable solid forms after solidification. These results demonstrate that plasma treatment can integrate waste destruction, oxidation, and immobilization within a single technological workflow, reducing external heat demand and enabling robust products for storage or further use. The findings provide an engineering basis for scaling plasma systems for radioactive-waste management with an emphasis on safety, efficiency, and sustainability.

In this paper the conditions for runaway electrons generation in streamer discharges are both theoretically and experimentally investigated. The discharge ignition is performed in a long quartz tube with external ring electrodes filled with low-pressure air. Gas pressure of 1 Torr is corresponding to the sea-level altitude of ≈47 km and falls within a range of 40–90 km, typical for red sprites observation. It is shown that the streamer discharge is ignited on the front of dielectric barrier discharge and plasma diffuse jet propagating towards the grounded collector is formed. The conditions for runaway electrons generation in gas-filled dielectric tube with external electrodes have been implemented. The spatio-temporal distribution of electron density, as well as energy distribution of electrons along the symmetry axis of tube, are obtained. It is shown that the highest values of reduced electric field and of electron kinetic energy are observed on the front of streamer at the trailing edge of voltage pulse.

We presented experimental studies on the synthesis of tungsten carbide powder by the vacuum-free electric arc method. The optimal parameters of plasma processing of the tungsten–carbon system were determined based on the results of temperature field distribution during vacuum-free electric arc synthesis. Temperature conditions are ensured in the reaction zone at certain parameters—the power supply current is 250–300 A, ensuring a temperature mode of 1700°C. The study of the mass balance showed that the greatest mass losses are observed with an increase in current to 300–350 A. X-ray phase analysis of the synthesized material revealed the predominance of the crystalline phase of tungsten carbide WC.