Vol 45, No 5 (2019)

Experiments on the acceleration of a flyer by a magnetic field make it possible to study the dynamic characteristics of matter on submicrosecond time scales. Megabar pressures at the Angara-5-1 facility are produced using the magnetic field of the current with a linear density of up to 5 MA/cm. In the previous experiments on the acceleration of a duralumin flyer, velocities of up to 10 km/s were achieved. The flyer motion was recorded by means of laser shadowgraphy. In this work, the efficiency of momentum transfer from a duralumin flyer to an initially immobile tungsten target was studied. From the kinematic parameters of the flyer motion before the impact and the motion of the flyer together with the target after the impact, the fraction of the flyer mass that transfer the momentum to the target was estimated. It is established that almost the entire mass of the flyer is involved in the impact process.

Results of experimental studies of local plasma parameters in the gas-discharge channel of a model single-stage plasma thruster with an anode layer (TAL) are presented. The electron energy distribution function and its dynamics along the middle line of the channel are determined. It is found that, as in a similar stationary plasma thruster (SPT), there are three groups of electrons: low-speed electrons with energies of about 8–12 eV, high-speed electrons with energies of 40–50 eV, and a relatively small group of electrons with intermediate energies. The experiments have shown that the generation regions and dynamics of these groups of electrons in the TAL under study differ from those in the SPT. The energy characteristics of the low-speed electron component are calculated and the dynamics of the high-speed and intermediate groups of electrons are analyzed according to the technique developed for SPTs. It is shown that, in the single-stage TAL, in contrast to the SPT, the condition of global isodrift over the entire channel is not satisfied and the zones of gas ionization and ion acceleration are separated more clearly. The generation region of high-speed electrons in the TAL under study differ from that in the SPT; however, the position of the peak of the energy distribution function of this group, as in the SPT, depends linearly on the plasma potential. As is commonly accepted by experts in SPTs, the appearance of the intermediate group of electrons is not related to the presence of the dielectric channel wall and finite near-wall conductivity.

A novel process is proposed to create high-energy particle populations in well-organized plasma structures surrounding nonaxisymmetric systems in which one or more components orbit around another. Binaries of black holes or neutron stars and light objects rotating around a massive object are examples of current interest. The relevant tridimensional and time-dependent gravitational potentials are shown to sustain the excitation of vertically localized ballooning modes in a plasma structure imbedded in a vertical magnetic field. These modes are viewed as composed of waves oppositely propagating in the vertical direction and can be excited when their frequency can match that of the orbiting frequency of one object around another. The formation of high-energy particle populations is predicted on the basis of the mode–particle resonance interactions associated with the mode components and the presence or the formation of a high-energy beam is not required. Rather, a vertical oscillatory force acting on the surrounding plasma structure is a necessary factor. High-energy flares associated with composite systems or envisioned precursors to the collapse of binary of compact objects are consistent with the presented theory.

The objective of this work is to study the behavior of surface layers of high-temperature metals in their interaction with a powerful pulsed plasma flow produced by a high-power ablative pulsed plasma thruster. This plasma generator produces plasma flows with a directed velocity of (7–9) × 10⁶ cm/s, an initial diameter of 1.5–2 cm, and a maximum number density of about 10¹⁸ cm^–3, as well as a maximum power of 5 GW. The main measured values are the residual temperature of the tungsten specimens and the evaporated mass. Also, metallographic analysis of the specimens was performed. The basis of the research method is to analyze the experimental data with the help of a numerical model describing the heating and evaporation of the material upon absorption of pulsed energy fluxes taking into account the evaporation kinetics based on the Hertz–Knudsen expression. Based on the developed numerical model and the obtained experimental data, the kinetics of evaporation of tungsten at high power fluxes to the surface (up to 1 GW/cm²) is investigated.

A new concept of plasma separation of spent nuclear fuel components in a variable-cross-section chamber with a nonuniform magnetic field is proposed. Numerical simulation performed in axisymmetric geometry in the single-particle approximation have shown that, in a nonuniform magnetic field of <1.6 kG, at voltages of up to 100 V, and for a chamber radius varying from 20 cm to 60 cm over a distance of up to 1 m, spent nuclear fuel components can be spatially separated into three mass groups: actinides with masses of m ~ 240 amu, used for subsequent recovery of the fuel; fission products with \(m = 70{-} 160\) amu; and light elements with \(m < 60\) amu, which primarily include the structural materials and associated gases (nitrogen, oxygen). Separation of the latter two groups is important for practical use, because it potentially reduces the cost of the further treatment of separated radioactive waste.

Modulational instability (MI) of ion-acoustic waves (IAWs) has been theoretically investigated in a plasma system which is composed of inertial warm adiabatic ions, isothermal positrons, and two-temperature super-thermal electrons (cool and hot). A nonlinear Schrödinger equation (NLSE) is derived by using reductive perturbation method that governs the MI of the IAWs. The numerical analysis of the solution of NLSE shows the existence of both stable (dark envelope solitons) and unstable (bright envelope solitons and rogue waves) regimes of IAWs. It is observed that the basic features (viz., stability of the wave profile and MI growth rate) of the IAWs are significantly modified by the superthermality of electrons and related plasma parameters. The results of our present investigation should be useful for understanding different nonlinear phenomena in both space (viz., Saturn’s magnetosphere and interplanetary medium) and laboratory plasmas (viz., hot-cathode discharge and high-intensity laser irradiation).

The electroacoustic waves, particularly ion-acoustic waves (IAWs), and their expansion in the medium of a magnetized collision-free plasma system has been investigated theoretically. The plasma system is assumed to be composed of both positively and negatively charged mobile ion species and kappa-distributed hot electron species. In the nonlinear perturbation regime, the magnetized Korteweg–de Vries (KdV) and magnetized modified KdV (mKdV) equations are derived by using reductive perturbation method. The prime features (i.e., amplitude, phase speed, width, etc.) of the IAWs are studied precisely by analyzing the stationary solitary wave solutions of the magnetized KdV and magnetized mKdV equations, respectively. It occurs that the basic properties of the IAWs are significantly modified in the presence of the excess superthermal hot electrons, obliqueness, the plasma particle number densities, etc. It is also observed that, in case of magnetized KdV solitary waves, both compressive and rarefactive structures are formed, whereas only compressive structures are found for the magnetized mKdV solitary waves. The implication of our results in some space and laboratory plasma situations is concisely discussed.

In order to study air discharge characteristics in the inlet of supersonic aircraft and explore an effective way to avoid such adverse regimes of discharge as spark, arc, or corona discharge, a nanosecond pulsed pin-to-plate discharge experiment is carried out for pressure ranging from 500 to 5000 Pa and temperature from 295 to 425 K. The study shows that glow-to-corona and corona-to-glow transitions can be realized by changing pressure. Specifically, with the temperature of 295 K and interelectrode distance of 10 mm, the pressures of corona discharge and glow discharge are 4500 and 1000 Pa, respectively, for the corresponding applied voltage of 4.56 and 8.25 kV. However, glow-to-spark transition cannot be obtained by varying pressure but increasing the applied voltage, which is a determined factor, and the peak voltage increases to 12.4 kV under spark regime. Overall, the regimes of discharge are jointly determined by interelectrode distance and pressure; but temperature could also effectively influence the discharge, the higher the temperature, the easier the breakdown is. The experiment results pave the way for follow-up further research on the characteristics of discharge in supersonic airflow.

In this research, the decomposition of CO₂ in CO₂/O₂ pulsed discharge was studied. The developed model is based on the physical processes involved in the discharge with the CO₂ plasma chemistry, the electrical circuit, and the Boltzmann equations. The fundamental chemistry of CO₂/O₂ gas mixture used in this work is based on a full set of processes regrouped in 113 reactions involving 21 species of the discharge. The obtained numerical results show the temporal variations of electrical parameters and species concentrations of the discharge. We have also studied the effect of some discharge parameters (gas pressure, dielectric capacitance, applied voltage, concentration of O₂ in CO₂/O₂ gas mixture, and frequency) on the discharge behavior.

Inactivation of spore microorganisms on a dielectric surface by a dielectric barrier discharge with plane electrodes was studied experimentally. It is shown that, at an average specific discharge power of 0.3 W/cm³ and exposure time of 0.5–60 s, the degree of inactivation amounts to three orders of magnitude and depends weakly on the exposure time.