Plasma Physics Reports最新文献

Selection of dust particles in three-dimensional plasma–dust trap in the electrodeless radio frequency inductive discharge in neon was studied for the first time. The discharge conditions and the discharge chamber design were chosen so that the dust structures of polydisperse quartz particles are created in the resulting dust trap. The structure lengths were of up to 1.5 cm and the number of particles in them was of up to 4000. Statistical analysis of the sizes of trapped particles has shown that under the conditions chosen the average particle size is close to 4 μm, and in a wide range from 0.25 to 1.0 Torr, it weakly depends on neon pressure. It was found that in the three-dimensional dust structure formed, the longitudinal interparticle distance changes in anomalously wide range, as compared to the dust structures formed in plasma of glow discharge. The characteristic size of the trapped particles was estimated based on the vertical balance of forces acting on dust particle. It was shown that, in terms of a number of parameters, the method of particle selection in radio frequency inductive discharge is preferable, as compared to similar method used in glow discharges in strata, and the dust trap applied can be used for studying three-dimensional dusty plasmas in the magnetic field.

The problem of calculating kinetic characteristics during electron drift in inert gases in a wide range of the reduced electric field strength: 0.001 Td < E/N < 10 000 Td is considered. For the case of a weak field E/N < 0.01 Td, there is little reference data, and the drift velocity, average energy, longitudinal and transverse diffusion coefficients and ionization coefficient for the cases of a weak field and a moderately strong field E/N < 100 Td were calculated using the method of dynamics of many particles involving collisions in accordance with the Monte Carlo procedure. For the cases of strong and superstrong fields 100 Td < E/N < 10 000 Td, the results of calculations for two models of electron departure from the system were considered and analyzed for the first time: (1) an avalanche model with multiplication; (2) a model with the most energetic electron in the system leaving the wall during the act of ionization or transition to the escape mode. Taking into account the appearance of new electrons in the system during ionization events under stationary current conditions made it possible to include the departure of electrons from the system to the wall with the determination of its potential into the consideration and, by analogy with the ionization coefficient, to introduce the definition of the electron runaway coefficient. For these two models, tabulated values of the electron runaway coefficient were obtained. An analysis and comparison of the calculation results with the table data was carried out. In addition, we present analytical approximations of the elastic and inelastic cross sections of electron–atom collisions depending on the collision energy that we obtained based on an analysis of the available theoretical and experimental data. They have physically reasonable asymptotics and can be recommended by us for widespread use.

Deuterium Z-pinch experimental studies [1] were carried out at the Angara-5-1 facility at a current of 2–2.5 MA with 100 ns rise time. Neutron yield in experiments ranged from 5 × 10¹⁰ to 8 × 10¹¹ neutrons per pulse. In order to explain experimental results, the two-dimensional MHD calculations were performed taking into account the generation of DD-neutrons using thermonuclear and beam-target mechanisms. MHD calculations of pinch dynamics, carried out taking into account the deuterium density distribution in the gas puff, satisfactory agree with voltage measurements. The neutron yield in the calculations ranges from 4 × 10¹⁰ to 1.5 × 10¹¹ depending on the deuterium density and the time delay between the start of gas puff and the moment of generator start-up. The energy of accelerated deuterons, which lead to neutron generation in the beam-target mechanism, is calculated to be from 55 to 900 keV, which is in satisfactory agreement with the estimates obtained [1]. An important difference between neutron generation in a fast gas Z-pinch and neutron generation in a dense plasma focus is that the contributions of thermonuclear and beam-target mechanisms to neutron generation in a fast gas Z-pinch are comparable, whereas in a dense plasma focus the main neutron generation mechanism is the beam-target mechanism.

The breakdown and discharge ignition in discharge tubes with a diameter of about 1 cm and a length of 80 cm in inert gases (neon, argon, krypton, and xenon) at a pressure of about 1 Torr are studied experimentally. The tube is illuminated by radiation from continuous or pulsed light sources in the visible spectrum range. A ramp voltage with a small slope steepness (of about 50 V/s) is applied to the anode of the tube. Previously, the authors established that under these conditions external illumination can increase the breakdown voltage in several times. This effect was explained by the appearance of a charge on the tube wall as a result of photodesorption of electrons from its inner surface. In this work, it is found that charging the wall begins only when the anode potential approaches the breakdown potential measured without illumination. In addition, it is found that during the increase in the voltage on the anode and charging the wall, the anode potential differs from the breakdown potential by a constant and small value (less than 200 V).

The paper gives a systematic presentation of the Wigner function method (Weyl formalism) for modeling the propagation and absorption of electromagnetic waves in anisotropic and gyrotropic dissipative media with spatial dispersion. A general kinetic equation for the Wigner function (tensor) is formulated, and its asymptotic expansion up to the second order for smoothly inhomogeneous and weakly dissipative media is constructed. As a result, a modification of the method of the kinetic equation for rays is proposed, based on the stochastic description of rays, making it possible to increase the accuracy of numerical modeling of wave problems with strong transverse inhomogeneity of the absorption coefficient without increasing the amount of calculations. The technique developed can be used to describe the propagation, absorption, and scattering of electron-cyclotron waves in high-temperature plasma of magnetic traps for controlled fusion in cases where standard modeling methods do not provide the necessary accuracy.

The properties of a plasma sheath are investigated numerically by using a fluid model in which a monoenergetic electron beam is taken into account. To suit the realistic environment, secondary electrons emitted from the wall surface due to collision between the electrons and the wall surface is considered. The result reveals that the effective emission coefficient depends on the emission generated by a monoenergetic electron beam when the temperature of a monoenergetic electron beam is high. The effective emission coefficient of secondary electrons changes monotonically with the increase of emission coefficient generated by beam electrons. Using the Sagdeev pseudopotential method, a modified Bohm criterion can be obtained. It is found that the ion Bohm velocity increases with increasing beam electron energy and emission coefficient generated by a monoenergetic electron beam. Moreover, when the emission coefficient generated by a monoenergetic electron beam is small, the wall potential decreases with increasing beam electron energy and concentration. When the emission coefficient generated by a monoenergetic electron beam is large, the opposite is true. It is also shown that a monoenergetic electron beam can cause an increase in the critical effective secondary electron emission coefficient, and the increase is nonmonotonic.

Based on the two-dimensional resistive magnetohydrodynamics (MHD) model, this study explores the impact of shear flow on the resonant magnetic perturbation (RMP)-induced double tearing mode (DTM). The results indicate that the effectiveness of shear flow in suppressing the double tearing mode is primarily dependent on the flow velocity at the outer rational surface. A notable finding is that, with higher flow velocities, the double tearing mode is effectively suppressed. However, in cases of very weak flow velocities, the shear flow still exerts an influence, but with a limited suppression effect. Specifically, it can only inhibit the inner island, while the outer island continues to grow under the influence of the resonant magnetic perturbation.

The radiation field of a multi-dimensional plasma formation can be substantially asymmetrical. Often, the luminosity of such an object is determined using one-dimensional models with various correction factors to account for the nonsphericity. In this work, a model is presented for the determination of the luminosity of asymmetrical plasma formations based on consistent multi-dimensional radiation–hydrodynamics calculation on the example of the scenarios of supernovae with an equatorial disk. The simulations were compared with the observations of the supernova SN2009ip. The bolometric light curves were determined for the observation of this object in the disk plane and from the pole. A conclusion was made that it is impossible to describe the multi-dimensional structure of the radiation field within the framework of the one-dimensional model with correction factors and that, rather, a full three-dimensional simulation is required.

The ion-acoustic instability in the tails of meteoroids as a result of their passage through the Earth’s atmosphere is studied and the conditions under which it develops are given. The development of this instability occurs as a result of the relative motion of the plasma of meteoroid tails and the dusty plasma of the Earth’s ionosphere. Dust, in turn, creates conditions when this instability can develop in a situation of approximately equal ion and electron temperatures, which is observed in the plasma–dust system under consideration. The mechanism of the excitation of ion-sound waves as a result of the development of the ion-acoustic instability in meteoroid tails is shown. The growth rates of the ion-acoustic instability and the characteristic times of its development are found. It is shown that the instability has time to develop during the time of passage of a meteoroid body in the Earth’s atmosphere and the formation of a meteoroid trail, which has values much greater than the time of development of ion-acoustic instability in the system under consideration. The wave vectors and velocities of meteoric bodies, at which the development of the ion-acoustic instability is expected, are found. It is noted that the instability can reach a nonlinear regime at possible large wave amplitudes.

Electric field on the surface of a metal electrode covered by a continuous dielectric film and immersed in plasma is calculated at negative electrode potential Ψ when parameter eΨ substantially exceeds electron temperature T_e (left( {frac{{ePsi }}{{{{T}_{e}}}} gg 1} right)). It is established that strong electric field with a magnitude of 1–10 MV/cm can appear inside the film at plasma density of 10¹²–10¹³ cm^–3 and electron temperature of T_e = 10 eV as a result of charging of the outer film 10–1000 nm in thickness surface by a flux of positive ions from plasma. The magnitude of the electric field at film discontinuities is comparable to that inside the film. The magnitude of the electric field at the surface of the dielectric film and at the film-free clean metal surface in plasma is substantially lower than that inside the film. Strong electric fields inside the film and at its discontinuities can lead to electrical breakdown inside the film and at its discontinuities. The electrical breakdown of the dielectric film can initiate the unipolar arcing on metals, drive microplasma discharges and form centers of explosive electron emission on metal surfaces in plasma.