Plasma Physics Reports最新文献

The ignition characteristics of a methane–air mixture in a single plasma channel maintained by a pulsed-periodic nanosecond discharge with a pulse repetition rate of 5 MHz are considered. The dependence of the ignition delay time and combustion wave formation on the discharge channel current is investigated. A key point is that high electric fields (~100–300 Td) existing during the first few nanoseconds of each cycle ensure mixture ionization and the efficient production of chemically active particles. The characteristic decay time of the generated plasma exceeds the pause time between pulses, resulting in a noticeable level of pre-ionization of the plasma channel before the next discharge pulse. After the discharge is switched off, combustion wave propagation is maintained for several milliseconds. Combustion of the combustible mixture occurs in a channel whose volume is two to three orders of magnitude larger than the channel created by the pulsed discharge itself. The obtained results allow one to conclude that the use of such a distributed multi-channel pulse-periodic discharge of nanosecond duration for ignition of combustible mixtures can be an alternative to spark ignition.

The paper examines the distribution of potential between the magnetic mirror and the plasma flow absorber in an open trap expander. The effect of ion flow velocity variation behind the mirror on the plasma potential is analyzed. The acceleration of the ion flow by the ambipolar electric field is considered. The influence of the ion flow deceleration on the potential distribution due to residual gas charge exchange is discussed.

A new plasma equilibrium configuration is found. It is a generalization of the known magnetohydrodynamic structure of Hill’s vortex type for the case of axial asymmetry with the toroidal wave number n = 3. The analysis is based on a solution to a system of coupled partial differential equations derived from exact equations of the three-dimensional equilibrium of static plasma (force balance) under the assumption of small asymmetry and in the absence of the main toroidal magnetic field. It is shown that the search for corrections to the basic axisymmetric equilibrium in the class of polynomials in powers of z (by analogy with Solov’ev solution) leads to an overspecified problem and requires satisfying compatibility conditions. The resulting solution contains two free coefficients that determine the amplitude of the toroidal inhomogeneity of a magnetic configuration. It also depends on the initial equilibrium parameters, namely, the elongation of magnetic surfaces in the basic configuration of a Hill’s vortex. The toroidal asymmetry of magnetic surfaces is accompanied by the appearance of a toroidal magnetic field, which can be oppositely directed and is absent in the basic vortex configuration. The shape of magnetic surfaces in (varphi = {text{const}}) cross-section differs significantly from the “axisymmetric” one. Corrections to the magnetic axis are calculated, which to ensure the sufficiency of expansion in the weak asymmetry parameter at the small gradient of (Psi ).

Low-temperature atmospheric-pressure plasma jets, which generate a broad spectrum of reactive oxygen species and produce periodic action of electric fields are a promising tool that can be used in plasma medicine. When a cold atmosphericplasma jet (CAPJ) is applied to cancerous tumors, determining the correct dosage is crucial for optimal treatment results with minimal side effects. In this study, to optimize the CAPJ characteristics, the configuration of the electric field in the streamer propagation zone between the nozzle and the target was modified using an additional ring electrode. It was shown that the magnitude and location of maximum discharge current can be controlled, which increases the efficiency and safety of using CAPJs in medical applications. A study was conducted of the screening properties of a hydrogel applied to the skin of tumor-bearing animals during CAPJ treatment. Studies of the combined effect of gold nanoparticles and CAPJs were continued, and results showing an effective deceleration of tumor growth rates in animals after a single CAPJ treatment combined with gold nanoparticles carrying antibodies to the TYRP1 protein, which is expressed by melanomas of different types, were obtained.

The plasma gas kinetic temperature in the reaction of synthesis of titanium dioxide (TiO₂) microparticles with copper (Cu) nanoparticles deposited on them is estimated from the radiation of a titanium oxide (TiO) molecule. The synthesis reactions have been initiated by microwave radiation of a powerful gyrotron in a mixture of titanium dioxide and copper powders. As a result, materials are obtained that include micro-sized titanium dioxide particles of rounded shape ranging in size from 10 to 200 μm with copper nanoparticles deposited on their surface. The copper concentration in the powder mixtures varied from 0.1 to 20 wt %. The microwave breakdown in the mixtures is provided by the use of a steel initiator. The gas kinetic temperature is estimated from the radiation spectrum of the TiO molecule γ-system in the range from 700 to 720 nm. The bands in this range are caused by electron transitions between the А³Φ–Х³Δ molecular states. It is shown that the synthesis is carried out at the same gas kinetic temperatures of 5500 ± 500 K, which do not depend on the copper content in the powder mixture.

The paper considers the main physical processes that determine flows of charged particles onto a negative metal electrode immersed in a fully ionized isotropic plasma. Equations are found describing the charged particle motion in the plasma both near the metal electrode under a constant negative potential ({{Psi }_{0}}) and far from it. The charged particle flows from the plasma to the electrode in the charge separation region near the electrode surface are calculated for large ratios of the electrode electric potential ({{Psi }_{0}}) to the plasma electron temperature ({{T}_{e}}): (e{{Psi }_{0}}{text{/}}{{T}_{e}} gg 1). The ion and electron current densities from the plasma to the electrode are calculated. It is shown that, in the specific case of interaction of a negative titanium electrode with a natural oxide film about 10 nm thick with a pulsed plasma with a density ({{n}_{i}} = {{10}^{{13}}}) cm^–3, as a result of charge transfer to the film surface by the ion flow from the plasma, electric voltages of about 6 V and a corresponding strong electric field of about 6 MV/cm arise inside the film over characteristic times of 5–8 μs. Such a strong electric field leads to electrical breakdown of the thin film and excitation of microplasma discharges on titanium. A reduction in the plasma density significantly reduces the probability of excitation of microplasma discharges on the surface of the metal electrode.

A kinetic approximation is used to analyze the effect of the beats between incident and reflected waves in the vicinity of the linear mode conversion region in magnetized plasma. It is shown that as a result, spatial modulations of the density profile of the equilibrium plasma and external magnetic field occur. The specific case of the Wendelstein 7-X stellarator plasma is considered.

The article presents calculations of the electron temperature based on the spectral lines of iron and platinum atoms in the plasma-chemical process of obtaining platinum catalysts: platinum nanoparticles on aluminum oxide microparticles as a carrier. The process was initiated by a microwave discharge in a powder mixture consisting of platinum microparticles and γ-Al₂O₃, as a result of treatment with powerful (up to 400 kW) microwave radiation pulses, the source of which was a gyrotron operating at a frequency of 75 GHz. It is shown that the process leads to the formation of platinum nanoparticles on the surface of aluminum oxide microparticles; the spectral characteristics of the process were measured, and the temperatures were estimated. The data obtained indicate the possibility of transferring platinum particles to the surface of aluminum oxide particles through the gas phase.

Metallurgical silicon has been refined in electron-beam plasma of water vapor. This method is based on converting hard-to-evaporate impurities into their volatile compounds in chemically active oxidative electron-beam plasma. Major metal impurities are removed during electron-beam refining of silicon in water vapor plasma at a sample temperature of 1430°C.

Emission of low-frequency barrier discharge plasma in neon at a pressure of 1.4–1.7 Torr formed by transitions between excited states of the Ne⁺ ion is studied in the wavelength range of 290–450 nm using kinetic spectroscopy methods. The difference in the relative intensities of ion lines at different stages of the plasma evolution is discussed: from direct excitation with ionization from the ground state of the atom by electron impact in the active stage (discharge), followed by a transition to the recombination afterglow as the electron temperature relaxes. The latter is due to the collisional-radiative recombination of doubly charged Ne²⁺ ions with electrons, creating at a density of the latter of [e] ≈ 10¹¹ cm^–3 the population flux of some Ne⁺* levels comparable to excitation by electrons at the stage of the plasma creation. A significant number of ion lines corresponding to transitions from states with the principal quantum number n = 3 contain an intermediate stage, the explanation of which is based on the experimentally confirmed hypothesis that the long-lived neon atoms in metastable states participate in their excitation. In contrast, the spectral lines of transitions from excited states of the Ne⁺* ion of 2s²2p⁴(³P₂)4f configurations do not have this stage.