Физика плазмы

Abstract

The frequency dependence of the energy and ion current at the output of an RF plasma source with SPT geometry has been investigated. It has been shown that the ion energy is maximum when operating at a frequency of 6.8 MHz. An increase in the operating frequency is accompanied by a decrease in ion energy. The ion current depends nonmonotonically on frequency. At frequencies less than 27.12 MHz, an increase in the ion energy is accompanied by a decrease in the current, and a decrease in the energy by an increase in the current. Increasing the frequency to 27.12 MHz does not lead to an increase in the ion current.

Abstract

Electric charging of dust grains lying on the surface of the Moon is caused by the action of the solar wind plasma and the solar UV radiation. Near the terminator and in the shadow the charges on dust grains are negative and not too high for electrostatic lofting of such grains. That is why very strong electric fields are required to explain dust motion above the surface. Due to this various factors are taken into account to obtain stronger electric forces acting on dust grains. In the present paper it is investigated how the dielectric permittivity of the regolith and subsurface layers influence charging of dust grains on the Moon. We show theoretically that the dielectric permittivity in some regions can provide stronger (one order of magnitude and even more) electric charges of dust grains on the surface than it was estimated before.

Abstract

A method for prompt estimation of a number of key parameters that determine the features of the evolution and dynamics of current sheets produced in laboratory experiments has been proposed and realized experimentally. The method is based on the analysis of time dependences of the integral plasma current during its first half-period. The transverse dimensions of the current sheets and the strength of the initial electric field that initiates the sheet formation can be estimated on the base of defining the inductances of both the entire oscillatory contour and the region where the plasma current flows. Data on the plasma conductivity can be obtained by measuring the active resistance of the plasma gap and the dimensions of the current sheet. It is shown that the conductivity increased under conditions that corresponded to an increase in plasma density, indicating a turbulent nature of the conductivity.

Abstract

Dust acoustic solitons and nonlinear periodic waves propagating in the ionosphere of Mars in plasma–dust clouds at altitudes of about 100 km have been considered. The dependence of the soliton amplitude on the charge of dust particles and plasma electron density has been studied. It is shown that an important factor influencing the soliton parameters is the adiabatic capture of plasma electrons (ions). The possibility of the existence of nonlinear periodic waves in the ionosphere of Mars has been studied. It is shown that the spatial period of the wave can be sufficient for its recording by a spacecraft. The possibility of the occurrence of dust acoustic wave perturbations in the ionosphere of Mars should be taken into account when processing and interpreting observation data.

Abstract

The system of MHD equations for the equilibrium states of plasma in a given potential field is reduced to a single differential equation.

Abstract

Nonlinear resonant interaction between the electromagnetic ion-cyclotron (EMIC) wave and magnetospheric electrons at the Cerenkov resonance, also referred to as the Landau or the zero-order cyclotron resonance, is investigated. Based on the data obtained on September 10, 2017, by one of the Van Allen Probe (RBSP) spacecrafts, the trajectory of a monochromatic wave packet in an inhomogeneous multicomponent plasma is found. The amplitude of the wave along the propagation trajectory is calculated taking into account not only the linear resonant interaction with protons and electrons but also variation of geometric factors such as the group velocity and the ray tube cross section. Numerical integration of the nonlinear system of equations describing the motion of electrons in the field of modeled packet of the EMIC waves revealed an important role played by nonlinear effects in the dynamics of resonant particles.

Abstract

The construction of van Kampen waves for various methods of describing quantum collisionless plasma is discussed. The linearized quantum kinetic equation, description in terms of individual wave functions, and quantum hydrodynamics equations are considered. It is shown that perturbation theory conserves the total plasma energy when described by wave functions.

Abstract

The paper presents the results of numerical simulation of the initial stage of expansion of plasma formations resulting from the injection of high-speed aluminum plasma jets into the Earth’s ionosphere at different altitudes corresponding to two “North Star” experiments. The influence of an artificial atmosphere represented by an air cloud on the plasma formation parameters in the North Star-I experiment is studied. Gas-dynamic parameters of plasma formations and their optical characteristics are determined. We present a comparison of the calculation results with the results of measurements of the luminosity curves in two wavelength ranges of photometers, which shows good agreement between the calculated and experimental data.

Abstract

The absorption of microwave radiation in the GDT open magnetic trap (Budker Institute of Nuclear Physics) was studied using a new scheme of electron cyclotron resonance plasma heating at the second harmonic, in which radiation in the form of the extraordinary wave was launched almost transverse to the plasma column. When performing numerical simulations, the full-aberration quasi-optical approach was used, which was verified using the first experimental data, obtained at the facility. The optimal scenarios using the new heating system were analyzed. It was found that in the current configuration, the total efficiency of microwave heating does not exceed 60%, which is considerably less than that planned when designing the system. This occurs due to the tangential reflection of heating radiation from the resonance region; this is a wave effect that was previously not taken into account within the framework of the geometric-optics approximation. It was shown that heating at the second harmonic does not result in excitation of the “overheating” instability of the electron component observed during heating at the first harmonic; on the whole, the wide power deposition profile is formed in this case. This is an advantage of the new scheme, since it makes it possible to avoid the development of MHD plasma instabilities associated with peaked power release at the axis of the plasma column.

Abstract

The results of the numerical simulation of a pulse-periodic nanosecond discharge are presented. An axisymmetric high-frequency (5 MHz) electric discharge in a pin-to-pin configuration is considered. Numerical models are used that take into account the chemical kinetics of high-temperature air and plasma chemistry, in which the reaction rates are determined by the magnitude of the reduced electric field. Preliminary results of plasma activation of atmospheric pressure air by a pulse-periodic nanosecond discharge are presented in order to intensify the production of chemically active particles (by the example of atomic oxygen).

Abstract

Selecting the most effective and biologically safe operation regimes of a cold atmospheric plasma jet (CAPJ) is a defining factor in developing the cancer treatments based on the CAPJ. Experimentally and numerically, by changing the pulse duration of the positive pulsed voltage, we determined the optimum CAPJ regimes with regular propagation of streamers and a maximum discharge current at a temperature T < 42°C. In these regimes, the CAPJ appreciably suppresses the viability of the cancerous cells. It was shown that adding gold nanoparticles increases the cytotoxic effect of the plasma jet and decreases the viability of the NCI‑H23 epithelioid lung adenocarcinoma, the A549 lung adenocarcinoma, the BrCCh4e-134 mammary adenocarcinoma, and the cells of the uMel1 uveal melanoma. The polyethylenglycol-modified gold nanoparticles with fluorescent labels were used to visualize the absorption of the nanoparticles by the cells. It was shown that the CAPJ stimulated the penetration of the nanoparticles into the cells when they were applied to the medium immediately before the CAPJ treatment or immediately after, which indicates a short-time increase in the permeability of the cell membrane.

Abstract

In 2023, the Thomson scattering diagnostics with tangential probing geometry was installed and put into operation at the T-15MD tokamak. The new system is based on a 100-Hz Nd:YAG laser with a pulse energy of up to 3 J at the first harmonic, λ = 1064 nm. The system allows measurements to be carried out throughout the plasma discharge with its duration of up to 10 s with a time interval of 10 ms. Laser radiation is introduced into the tokamak vessel in the equatorial plane, passing through the entire plasma volume from the inner to the outer periphery of the plasma. The scattered radiation acquisition system is located inside the equatorial port of the facility. The range of scattering angles is from 11° to 56°. The recording system is based on 10 polychromators on interference filters. Using this diagnostics, the electron temperature and density have been measured in the experimental campaign at the end of 2023. The system operation was demonstrated throughout the entire tokamak discharge in a wide temperature range and with a discharge duration of up to 2 s.

Abstract

The radial distribution of the Bz field at a distance of 35 cm from the generation region of the axial jet emission (the anode surface of the setup) has been studied using the PF-3 plasma-focus facility. The measurements have been performed using multichannel magnetic probes located in the flight chamber of the facility. This has made it possible to measure the magnetic field distribution at 18 points on both sides of the flight chamber axis. The magnetic probes have been calibrated both in absolute value and in the magnetic field direction. An external multi-turn solenoid has been used to create the initial longitudinal (poloidal) magnetic field. The solenoid power supply circuit has allowed obtaining different Bz field directions: along or against the facility axis. It is shown that the poloidal field distribution reaches its maximum in the bunch center and decreases at the periphery, regardless of the presence of an external magnetic field. The Bz field has a radial distribution Bz(r), close in shape to the magnetic field distribution of the solenoid. The work is performed within the program for the simulation of jets of young stellar objects.