Plasma Physics Reports最新文献

The 2D code developed by the authors for calculating the penetration of neutral particles from the chamber wall to the center of the plasma created and confined in the L-2M stellarator has been verified. In the range of operating plasma densities (1 × 10¹⁹ m^–3 < n_e < 3 × 10¹⁹ m^–3), good agreement with the results of calculations performed using the ASTRA code has been obtained. The 3D and 4D simulations of the penetration of neutral particles from the chamber wall to the central plasma region have been performed. It has been shown that the 2D simulations overestimate the concentration of neutral particles in the plasma central region, as compared to the 3D and 4D models, which use ion velocity distributions closer to the real one.

A detailed study of the generation of slow extraordinary (SE) waves in the Earth’s magnetosphere has been carried out. Assuming that energetic electrons are distributed in accordance with the (kappa )-function with a loss cone, the instability growth rate of SE waves is calculated and its dependence on both the parameters of the hot particle distribution function and the cold particle density, characterized by the ratio of the electron plasma frequency to the electron cyclotron frequency, ({{omega }_{p}}{text{/}}{{omega }_{c}}), is studied. This ratio is one of the key parameters of the problem. For various ({{omega }_{p}}{text{/}}{{omega }_{c}}) values, the dependences of the instability growth rate on the parameter (kappa ) of the distribution function, the loss cone parameter (l), and the temperature of the distribution and its anisotropy are obtained. A nonmonotonic, quasi-periodic dependence of the growth rate on the ratio of the frequency to the electron gyrofrequency, which manifests itself in the dependence of the equatorial growth rate on the (L)-shell or the dependence of the growth rate on the latitude on a fixed (L)-shell, is revealed and explained.

A brief review of theoretical studies of circumlunar dusty plasma, the important factors in the formation of which are electrostatic processes and impacts of micrometeoroids on the lunar surface, is given. Observation data of dust particles in the vicinity of the Moon, obtained within the “Luna-25” mission, are described for the first time. It is shown that there is at least one reliable observation of a dust particle either of lunar origin or associated with the high-speed Perseid stream. The need to improve the Lunar Dust Monitor device on the “Luna-27” lander is discussed. The improvement is associated with the need to install a rod for placing electrostatic sensors at a sufficient distance from the device, which is desirable to reduce disturbances of the surrounding plasma and the near-surface electrostatic field because of the influence of the lander.

The Hard X-Ray collimation system was installed at the T-15MD tokamak (major radius of R = 1.48 m, minor radius of a = 0.67 m, elongation of k = 1.7–1.9, triangularity of δ = 0.3–0.4, toroidal magnetic field of B_T = 2 T, plasma current of up to I_p = 2 MA, and discharge duration of up to 30 s) to provide the possibility of measuring the spatial and temporal evolution of runaway electron beams. The diagnostic is based on LaBr₃(Ce) scintillation detectors, witch provides energy spectrum measurements for energies form 0.3 to 10 MeV. Monte Carlo simulation of the shielding efficiency in the GEANT4 environment showed that the collimator provides 2° field of view (FOV). Horizontal and vertical FOV movement along the plasma cross-section is arranged by a rotating base and screw support elements. An algorithm for processing the signals from the scintillation detectors with a graphical user interface and data visualization is used for reconstruction of the spectra. The results of testing the detector in a laboratory setup and in preliminary experiments carried out with the T-15MD tokamak in which runaway electrons beams were generated are presented.

The article considers different methods of divertor plasma diagnostics planned for using in the T‑15MD tokamak. Technical problems arising during operation of optical systems in the divertor zone are discussed, including degradation of in-vessel optical elements. The main attention is paid to the conceptual design of the “Passive Spectroscopy in Divertor” diagnostic system. The optical system, including in-vessel mirrors, and methods for protecting its components from the negative effects of plasma are described in detail. Using synthetic diagnostics and numerical simulation methods, the possibility of solving the problem of tomographic reconstruction of the two-dimensional profile of plasma radiation in the T-15MD divertor is demonstrated. Based on the results presented, it was concluded that passive spectroscopy can be used for obtaining data on plasma parameters in the divertor with good spatial resolution, which will make it possible to study the physics of processes and monitor the operation of the T-15MD divertor, including the operation in detachment regime.

The paper presents a computational and theoretical analysis of kinetic processes in methane, nitrogen, and oxygen mixtures for non-self-sustaining direct current discharges supported by an electron beam. Within an approximate approach, the kinetic coefficients in plasma under the simultaneous action of an applied electric field and an electron beam are determined. In a zero-dimensional (spatially homogeneous) approximation, the quasi-stationary composition of charged particles is calculated. The rate constants for generation of chemically active neutral particles of various types in plasma are calculated along with the energy efficiencies (G-factors) of the production of these particles depending on the magnitudes of the reduced electric field and the beam current. Similarity rules are proposed for the relation between the rates of production of active particles under the action of an electric field and an electron beam. It is shown that, by varying the applied field, it is possible to influence the composition of the produced hydrocarbon radicals.

Diagnostics based on using the contactless emission spectroscopy method are discussed and measurements results in experiments with helicon plasma at an experimental device used for studies of the plasma processes in a helicon discharge are presented. Argon and helium were the working gases. The radial distribution of the electron temperature was measured as well as the radial distributions of the atom and ion temperatures in different cross sections of the plasma flow, and the temperature cross sections along the installation axis. The plasma ionization coefficient was calculated, and its dependence on the electron temperature was determined.

The results of a numerical study of the configuration of chains of dust particles levitating in a gas-discharge plasma are presented. The studies have been carried out using an iterative model that self-consistently describes the motion of ions and dust particles under the action of an external electric field, an electric field (Coulomb) of each charged dust particle, a field of the plasma space charge (ions and electrons), which screens the charges of dust particles, and gravity for dust particles. The structural parameters of the chains of dust particles were calculated for different numbers of particles in them. It was found that when new particles are added to the chain, the center of the chain rises above the lower electrode. This is due to both a decrease in the charges of the lower dust particles due to the focusing of positively charged ions behind the upper particle, and a significant decrease in the ion drag force on the lower particles of the chain as a result of structural rearrangement of the entire chain. It is shown that the reduced charge of the chains decreases, and the reduced length of the chains has a maximum depending on the number of particles.

In the Earth’s atmosphere at altitudes of 80–120 km during high-speed meteor showers, conditions are created for the appearance of a dusty plasma system. As a result of the development of the modulation instability of the electromagnetic waves, in the dusty ionospheric plasma, linear and nonlinear dust acoustic waves can be excited. The new phenomenon observed above the Scandinavian countries, the so-called dunes, which are, in fact, periodic wave structures that extend to far distances in the horizontal direction and have a characteristic spatial period of about 45 km, can be one of the manifestations of the nonlinear dust acoustic waves. The maximum number of dunes was recorded in October, when the Draconids meteor shower is observed. We consider the nonlinear periodic dust acoustic waves that can develop in the dusty plasma with parameters that correspond to the ionospheric plasma during meteor showers.

A mechanism of formation of plasma-dust system above the surface of Enceladus, the Saturn moon, illuminated by the solar radiation is proposed. It is demonstrated that the photoelectric effect caused by the sunlight and the influence of the solar-wind plasma create conditions for lifting of dust particles above the surface of the moon as a result of electrostatic repulsion. Based on a self-consistent model describing the electrostatic field and plasma components, including photoelectrons emitted from the Enceladus surface and those emitted from the surface of the dust particles, distribution functions of photoelectrons, dust particles, and their electrostatic charges are determined as functions of altitude and the angle between the local normal and the direction to the Sun. Also determined are the altitude profiles of the electrostatic fields for the corresponding angles between the local normal and the direction of the solar radiation. It is demonstrated that the photoelectric effect plays an important role in formation of dusty plasma near the Enceladus surface despite considerable distance from the Sun. It is established that concentration of photoelectrons above the Enceladus surface can exceed concentration of electrons and ions of the solar wind by an order of magnitude, and the size of the levitating particles is larger than the characteristic size of dust particles lifted above the surface of the Moon due to the fact that Enceladus is much smaller than the Moon. On the contrary, the size of particles levitating above Enceladus is much smaller than the size of particles levitating above the surface of celestial objects smaller than the Enceladus, e.g., the Martian satellites Phobos and Deimos.