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The current state of research on measuring the electron concentration in low-temperature plasma in the vicinity of a strong shock wave, which simulates the conditions of the descend spacecraft entry into the Earth's atmosphere, is considered. Various physicochemical processes leading to the formation of low-temperature plasma both ahead of the shock wave front and in the shock-heated gas are analyzed. A critical review of various plasma diagnostic methods is made, and their advantages and disadvantages are noted. Numerous experimental data on measuring the electron concentration in various shock-heated gases in various conditions are analyzed. [ABSTRACT FROM AUTHOR]

A series of probe measurements to determine the electron concentration in the gas ahead of a strong shock wave (SW) front are carried out using a modified double-diaphragm shock tube (DDST-M) of the Institute of Mechanics, Moscow State University. At the same time, the light flux from the region of the shock-heated gas is recorded, which makes it possible to calculate the electron concentration behind the SW using the spectroscopic method. The experiments are carried out in air, oxygen, and nitrogen at SW velocities ranging from 8.3 to 11.3 km/s and an initial pressure of 0.25 Torr in the low-pressure chamber (LPC). The dependencies of the electron concentration on the SW velocity and the distance from the observation point to the SW are obtained. The spectroscopic measurements make it possible to determine the dependence of the electron concentration on the composition of the gaseous medium. The obtained data are compared with the experimental data of other authors. [ABSTRACT FROM AUTHOR]

At the large-scale Krot facility (Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences), a new device was developed for laboratory simulations of the effects of the interaction of ultrawideband electromagnetic pulses with the partially ionized atmosphere and ionosphere: the "gigantic" coaxial line with a length of 10 m and diameter of 1.4 m that is filled by the decaying plasma of the inductive discharge. Two radiofrequency methods of wave diagnostics used in the device are described, the cutoff method and the wave interferometer, which can be used to determine the electron density of the plasma in the line in a wide range of values, Ne = 107–1011 cm–3. The measurement results are compared with the values obtained by the contact diagnostic, a probe with a microwave resonator. The interferometric method is implemented taking into account the nonuniform distribution of plasma density both along and across the transmission line, which, in the working range of pulsed and continuous diagnostic signals, is an oversized waveguide. The specific features of application and the limitations of the contact (probe) and contactless (wave) methods of diagnostics are discussed, taking into account the nonuniform plasma distribution in the coaxial line and the specific features of its construction. [ABSTRACT FROM AUTHOR]

Within the framework of the quasiclassical trajectory method on semiempirical diabatic potential energy surfaces, we have considered the existence regions for direct three-body recombination Cs+ + Br– + R → CsBr + R (R = Kr, Xe, Hg) in the case where the encounters of the Cs+ and Br– ions are central and the delay parameter vanishes. The recombination regions are determined using a much more precise procedure than in the previous works. Particular attention is paid to the recombination opacity functions and to the role of the orientation angles in the outcome of a three-body collision. The performed calculations demonstrate a great complexity of the structure of the recombination regions. [ABSTRACT FROM AUTHOR]

A self-consistent unified model of direct current (DC) gas discharges in molecular gases describing the processes both in the discharge gap and in the electrodes is developed. Numerical simulations of the formation of parameters of various modes of DC discharge in nitrogen at atmospheric pressure in a wide range of current densities have been carried out in the one-dimensional approximation. As a result of numerical experiments, the dependence of voltage drop across the discharge on current density is obtained, which describes various discharge modes: from Townsend through normal and abnormal glow to arc discharge. The distributions of the main mechanisms of heating the electrodes, the values of their temperatures at the boundary with the discharge, depending on the current density, and all plasma parameters for various modes of a dc discharge are presented. It was shown that in the plasma region the dominant role in gas heating belongs to vibrational-translational relaxation, as well as to the reactions of dissociation of N2 molecules by electron impact and quenching of electronically excited N2 molecules. In the cathode layer, the dominant role in gas heating belongs to Joule heating by ion current. The scenario of formation of an arc discharge with free cathode mode when electrons are the predominant charged particles in the cathode layer was shown. [ABSTRACT FROM AUTHOR]

The goal of this paper is to assess the possibility of using a new three-ion ICRF heating scheme on the spherical tokamak Globus-M2. In the first place, the operating frequencies and positions of cyclotron harmonics were found. Matching with frequency band of RF system of Globus-M2 was made. The absorption of electromagnetic waves was modeled using a one-dimensional full-wave code. Since the appearance of high-energy particles is expected in the three-ion ICRF scheme of heating special attention is paid to a comparing the estimates for generated particles energies with their confinement in tokamak Globus-M2. [ABSTRACT FROM AUTHOR]

A time-dependent nonlinear model that describes the generation of vortex patterns of dust grains in a magnetized dusty plasma [Nebbat and Annou, Phys. Plasmas 17(9), 093702 (2010)] is revisited. The effect of the magnetic field on ions is investigated. Numerical results confirm the existence of a vortex low-density core surrounded by a high-density wall as well as dust density ripples, in agreement with experimental data. [ABSTRACT FROM AUTHOR]

The theoretical model for increasing peaking of radial distribution of plasma thermal energy and plasma energy confinement time improvement due to the formation of current profiles those provide the increased value of the safety factor at the outer plasma boundary is considered. The model for the formation and stationary maintenance of the peaked current density profiles those ensure the maintenance of plasma column equilibrium state with increased value and conservation of at the magnetic axis is developed. The model is based on the significant ramp down of the current maintained by the inductor with simultaneous central ECR heating and electron cyclotron current drive (ECCD) switching on. It is shown by the computer simulations of the self-consistent time evolution of turbulent plasma for the conditions of T-10 and T-15MD tokamaks that in the shot scenarios with three- or four-fold decrease in the current at the ECRH stage of shots it was achieved an approximately two-fold enhancement of the electron and ion temperatures at the axis of the plasma column as compared to the standard shots with the same heating powers. [ABSTRACT FROM AUTHOR]

To study the physical mechanism of the separation between heavy and light species in the vacuum arc devices with deuteride cathodes, a three-fluid model based on magnetohydrodynamic (MHD) theory is established. In the model, different kinds of species are considered to be different kinds of fluids, and their physical parameters are calculated separately. Moreover, the distribution of arc current is calculated by the generalized Ohm's law, and the ionization and recombination of species are taken into account. In the paper, the two cases where the cathode is Zr or ZrD0.67 are simulated, respectively. The results show that in the case of ZrD0.67 cathode, the separation of light and heavy species is remarkable. Because of D's lighter mass and lower mass-to-charge ratio, the distribution of it is more uniform. In addition, the differences between species also lead to large differences in other physical characteristics, such as ion velocity, ion temperature, and so on. Notably, the desorption and ionization of deuterium lead to a decrease in plasma temperature. The self-generated magnetic field of the arc has an inhibitory effect on the expansion of each species, and it is more obvious for ions with lower mass-to-charge ratio. The simulation results are consistent with the experimental results. The theoretical analysis can provide theoretical guidance for the improvement of vacuum arc devices with composite or gas-saturated cathodes. [ABSTRACT FROM AUTHOR]

Deep learning models for identification and subsequent mitigation of tokamak plasma disruption have recently shown great promise for reliable predictions for machines other than the one on which it has been trained. The performance of such artificial intelligence (AI)/machine learning (ML) models strongly depends on the training data. Considering the sparse availability of universal high quality data underscores the requirement for synthetic data for the training of the AI/ML models. Synthetic data generation methods reported in the current literature have limitations in terms of quantity, diversity and preserving the temporal dynamics of the experimental seed data (SD). The article presents generative adversarial networks based procedure capable enough to generate unlimited device‐independent temporal evolution of tokamak plasma current. The synthetic data improves with the employment of the classified SD while retaining the characteristics of the original data. The procedure offers a substantial volume of synthetic data with a very impressive diversity, thereby ensuring the requirements for successful AI/ML model training. [ABSTRACT FROM AUTHOR]

We present the results of experimental studies of the intensity of vacuum ultraviolet self-radiation (VUV) of the discharge in hydrogen sustained in an open magnetic trap by the high-power radiation of a gyrotron (frequency f = 28 GHz and power Pgyr = 5 kW) under conditions of electron cyclotron resonance (ECR) in the continuous regime. The optimum system parameters were determined for the generation of VUV radiation by the plasma of the ECR discharge. It was shown that the radiation power in the wavelength range λ = 120–160 nm reaches W = 0.75 kW, which corresponds to an efficiency of η = 20%. [ABSTRACT FROM AUTHOR]

Based on the model of a collapsing magnetic trap, we consider the influence of the temperature of a Maxwellian flare plasma on the efficiency of the betatron acceleration of quasi-thermal fast electrons in the cusp region of coronal loops. We show that an increase in the temperature causes a sharp growth (by 6–8 orders of magnitude) in the number density of quasi-thermal electrons which are capable of overcoming the "Coulomb loss barrier." This suggests the necessity of background plasma preheating in the cusp region to MK, for which the betatron mechanism can be responsible. We discuss the connection between the impulsive phase of flare energy release and the X-ray precursors of solar flares. [ABSTRACT FROM AUTHOR]

Dependences of the kinetic and transport coefficients of electrons in neon are calculated by the Monte Carlo method in the range of reduced field strengths E/N from 15 to 1500 Td. The calculated dependences are compared with the results obtained by solving the kinetic equation in the Lorentz approximation. It is shown that this approximation is violated in strong electric fields, which leads to noticeable differences in the values of the transport coefficients calculated using both methods. To verify the calculations, a comparison was made with the measurement data available in the literature. It is also shown that the diffusion-drift approximation poorly describes the spatiotemporal evolution of the electron number density in neon in fields greater than ≈500 Td. [ABSTRACT FROM AUTHOR]

An analytical solution of the Poisson's equation is found for the electric field on the surface of the electrode immersed in a homogeneous non-isothermal collisionless plasma consisting of electrons and single-charged ions with charge e, with electron temperature Te and high values of negative electric potential Ψ when the parameter |eΨ|/Te ≫ 1. It is found that the plasma layer L with violated quasi neutrality near the high-potential electrode increases compared to the Debye length rD proportionally to the parameter [eΨ/2Te]3/4, as L = rD[eΨ/2Te]3/4. The electric field was calculated on the surface of the negative electrode in plasma. It is shown that in a laboratory plasma with density in the range 1010–1013 cm–3 and electron temperature from 1 to 10 eV, at high potential for the parameter eΨ/Te ≫ 1, the electric field calculated by the obtained formula E = Ψ/L near the surface of the electrode up to 200 times lower than the fields calculated by the classical formula E = Ψ/rD, which was obtained at low potential and for the parameter eΨ/Te ≪ 1. [ABSTRACT FROM AUTHOR]

The characteristics are determined of three-dimensional dust structures created in three dust traps formed in glow discharges and compared to each other. The following dust traps turn out to be stable in the applied magnetic field with induction of up to 2 T: the standing stratum, the region of the current channel contraction (inside the special dielectric insert), and the discharge region located in highly inhomogeneous magnetic field. For each of these dust traps, the geometric characteristics of three-dimensional dust structures formed and distinctive features of their rotation dynamics are presented, such as the longitudinal and transverse sizes (with respect to the magnetic induction vector), angular velocities, and their longitudinal gradients. Differences are analyzed in the experimentally obtained characteristics of three-dimensional dust structures formed in glow and RF discharges in the strong magnetic field. [ABSTRACT FROM AUTHOR]

A system of one-dimensional multigroup equations for the first three moments of the electron distribution function in the range of intermediate and high energies is derived. The system includes equations for the balance of concentration, flux density and momentum flux density of electrons and it is intended for numerical simulations of processes involving fast electrons in weakly ionized cold plasma. [ABSTRACT FROM AUTHOR]

Under conditions of glow discharge in the strong magnetic field, three-dimensional dust structures were created in the He, Ne, and Ar working gases in three types of dust traps (in standing stratum, in the region of current channel narrowing, and in the region of nonuniform magnetic field). These structures are stable in the fields of the order of 2 T. In all traps, the rotation dynamics have been studied of horizontal (perpendicular to the magnetic field) cross sections of dust structures, their angular velocities has been measured, and the nonuniform angular velocity distributions in the dust structure volumes have been measured. For the first time, for the trap in the region of current channel narrowing, the data are presented in the range of magnetic inductions of up to 2.5 T. Such magnetic fields correspond to the Ne+ ion magnetization parameter of approximately 2 and the ion cyclotron radius comparable to the shielding distance. In the fields higher than 1.5 T, the angular velocity of the structure rotation increased to 50 s–1, which is a record-breaking fast rotation of dusty plasma. For each of the traps under study, the geometrical features of the dust structures are described. [ABSTRACT FROM AUTHOR]

An alternative conclusion to the work of W. R. Hoegy ["Thermal electron heating rate: A derivation," J. Geophys. Res. 89(A2), 977–985 (1984)] is presented, and rigorous analytical expressions for heating thermal Maxwellian electrons by the fast part of the energy distribution function (EDF) with an arbitrary dependence on energy are obtained. This makes the calculation of thermal electron heating under specific conditions possible, as well as scaling the obtained results. For the most convenient bi-Maxwell approximation of the EDF, comparatively simple analytical expressions for heating, convenient for practical calculations, are obtained. It has been shown that these expressions are in good agreement with the results of the fundamental Hoegy's work. Analytical expressions for heating thermal electrons by fast electrons, with a power-law distribution dependence on energy, are also presented. [ABSTRACT FROM AUTHOR]