Plasma Physics Reports最新文献

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.

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.

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.

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.