Plasma Physics Reports最新文献

The dielectric constant and the dispersion relation of the Ordinary mode (O-mode) instability has been discussed by using the Vlasov kinetic model in the presence of the Heaviside distribution function. The Heaviside distribution includes relativistic effects for both the parallel and perpendicular streaming. It is noted that the relativistic effects play a destabilizing role for the O-mode at higher magnetic field in comparison to the non-relativistic case. The growth rate of O-mode instability is calculated analytically for different values of parallel and perpendicular streaming. It is shown that the parallel streaming destabilizes the O-mode where as the perpendicular streaming provides a stabilizing effect. The results of the non-relativistic O-mode instability have been retrieved under limiting case.

The high-confinement mode in tokamaks (H-mode) is characterized by high pressure gradients at plasma edge, which results in the appearance of edge localized modes (ELMs). They are studied at the Globus-M2 spherical tokamak too, where edge localized modes are observed mainly in regimes with neutral beam injection. One of the ways for studying ELMs is the use of the Doppler backscattering (DBS) diagnostics installed at Globus-M2. It makes possible to estimate the amplitude of plasma density fluctuations and measure the radial electric field E_r. In this work, the effect of edge localized modes on the E_r field is studied in the radial range 0.4 < ρ < 1.1. It is shown that during ELMs the electric field increases in the entire measurement range. This indicates that ELMs affect the inner plasma regions as well. This is not consistent with the general ideas concerning the peripheral localization of ELMs, but is confirmed experimentally not only at Globus-M2. In addition, the results for the regime with ELMs are compared with those for the regime with limit cycle oscillations (LCOs) and it is shown that during LCOs such effect is not observed.

Experiments on compression of cascade tungsten wire arrays with reduced inductance at the final stage of pinching aimed at increasing the specific concentration of plasma energy of the high-current Z‑pinches were carried out. The experiments were conducted at the Angara-5-1 facility at load current of up to 4 MA. The highest radiation power per unit pinch length were obtained using the cascade wire arrays in which mass per unit length of the inner wire array with reduced inductance was in the range between 1 and 1.5 that of the outer wire array. The soft X-ray radiation power of P ~ 11 TW was obtained from the 1-cm-long pinch. The specific yield of the soft X-ray radiation was in the range of 130–140 kJ/cm. The total and specific powers of the pinch radiation obtained upon compression of the cascade load with reduced inductance exceeded the total and specific powers of the pinch radiation obtained by compression of a “standard” wire array with a length of 1.6 cm with the same parameters (7–8 TW and 5 TW/cm, respectively). The yield of the soft X-ray radiation did not change upon reduction in the length of the emitting pinch from 1.6 to 0.6 cm. The compression dynamics of such a load is indicative of an increased role played by the magnetic field of the current flowing in the inner cascade in interaction of the cascades. A variant of using interaction of the cascade-array shells via the magnetic field of the inner-cascade current as applied to the scheme of the statistical “hohlraum” with indirect irradiation of spherical targets is proposed. The scheme enables entrainment of part of the current by the inner wire array that confines the statistical “hohlraum.” In this case, interaction of cascades allows using nearly entire kinetic energy of the accelerated outer shell for generation of radiation in the statistical “hohlraum” by two forming near-electrode pinches.

The set of equations is obtained that describes the nonlinear three-dimensional dynamics of magnetosonic waves. Plane solitary waves propagating at a small angle to the guiding magnetic field have been studied. Three-dimensional spatially localized waves have been qualitatively studied.

Plasma was heated at the second harmonic of electron cyclotron resonance (ECR) in the L-2M stellarator and the T-10 tokamak. The concept of equivalent tokamak and stellarator discharges was extended to the case of both full and partial absorption of EC power. Comparison of experimental electron temperature profiles with profiles calculated using the canonical profiles transport model allows us to estimate the efficiency of ECR heating in the L-2M discharges without suprathermal electrons, which distort the distribution function, preventing reliable measurements of temperature. The dependence of the ECR heating efficiency on the plasma density was obtained, describing experiments on the L-2M and TJ-II stellarators, and on the T-10 tokamak. The energy characteristics (the stored energy and the confinement time) for L-2M discharges were calculated. Predictions for ECR heating in the T-15MD tokamak are considered. The features of solving the ill-posed transport problem for the L-2M are discussed.

The results of a study of a pulsed short-arc unlimited high-pressure xenon discharge as a source of UV radiation are presented. A theoretical analysis of the possibility of increasing the efficiency of xenon discharge radiation in the UV region of the spectrum is performed, the design of a three-electrode flash lamp is described, and the electrical, brightness and spectral characteristics of the source being developed are studied.

A method for activating water by plasma of an electrodeless torch discharge in a microwave electromagnetic field in argon in an environment of water vapor, at atmospheric pressure, to obtain a pure solution of hydrogen peroxide H₂O₂ without impurities in distilled water is proposed. It is shown that the main mechanism for the formation of atomic hydrogen H^• and hydroxyl HO^• radicals in the water decomposition is photolysis under the influence of excimer vacuum ultraviolet radiation of argon plasma. Hydrated electrons can be an additional source of radicals in liquid water when the plasma torch comes into contact with the water surface. Today plasma technologies are widely used to produce activated water containing hydrogen peroxide, to solve environmental problems, to increase productivity in agriculture, and for medical use.

The effect of the spatial distribution of electric potential on the separating properties of the plasma mass separator that operates in a configuration with crossed radial electric and longitudinal magnetic fields is studied. The single-particle approximation is used to obtain analytical expressions that connect the electric potential distribution and the angular mass spectrum. A mathematical algorithm is described that allows one to recover the distribution of electric potential from the given shape of the mass spectrum. It is shown that the local inhomogeneity of the electric potential profile allows one to achieve the deposition of mass groups in the diametrically opposite regions of the separator. Data is presented that confirms the possibility of creating experimentally both the positive and the negative local inhomogeneity of the potential. The results of this work can be used to increase the efficiency of the process of plasma mass separation of ions of different elements.

A one-dimensional (1D) fluid model is developed to investigate the effect of multi-frequency excitation consisting of (N) consecutive harmonics on the charge of a single dust grain in a weakly collisional capacitively coupled plasma discharge. The spatial distributions of the electron density, the electrons temperature, and the charged particle flux are obtained and analyzed under the effects of the number of harmonics. It is shown that the number of harmonics considerably affects the discharge properties and the sheath thickness. In order to analyze the charge of an injected dust particle under the effect of different operating parameters, the model takes into account the electron and ion currents, as well as the effect of collisions between ions and neutral atoms. The results showed that as the number of harmonics increases, the particle charge increases in the powered sheath region while it decreases in the grounded sheath due to the electrical asymmetry effect. However, the charge remains constant in the central region where the electron temperature is constant. The present study further shows that the gas pressure and the driving frequency affect the dust charge oppositely, where an increase in pressure leads to a decrease in the dust charge, especially in the sheath regions, while the particle charge negatively increases as the driving frequency increases for all excitation waveforms.

Using chromatography, the gas composition in a cold plasma jet, which is a flowing afterglow of a microwave glow discharge at atmospheric pressure, is analyzed. The plasma jet is formed by the interaction of the discharge plasma with atmospheric air behind the outlet of the 6-electrode plasma torch, electrical power to which is supplied from the waveguide microwave (2.45 GHz) plasmatron. An analysis of the gas samples of the jet shows that when plasma-forming argon flows through the microwave discharge, hydrogen and methane are formed behind the discharge region, and the concentration of carbon monoxide increases by 5–6 times. The reactive oxygen species in the cold plasma jet is studied using liquid chromatography of an aqueous solution of isopropyl alcohol after treatment with the plasma jet. It is found that because of plasma treatment, partial oxidation of isopropyl alcohol to acetone occurs. This makes it possible to consider acetone as an indicator of reactive oxygen species (hydroxyl radicals, atomic oxygen and ozone) in a cold plasma jet.