Calculation of the field and current density distributions in a non-self-sustained discharge in the discharge chamber of a CO laser

Two-dimensional spatial distributions of the electric field and current density in a non-self-sustained discharge controlled by a fast electron beam were calculated in the quasineutral plasma approximation. The calculations were carried out for a gas-discharge chamber with an antistreamer electrode grid placed in parallel to the output window of the ionizer. The voltage drop near the grid surface that appears due to the inhomogeneity of the spatial distribution of the current density was calculated. The fraction of the discharge current that passes the grid and flows onto the foil separating the vacuum volume of the ionizer from the gas-discharge chamber was estimated. The dependence of the calculated values on the geometric parameters of the electrode grid and its position with respect to the output of the ionizer was analyzed.     

Probability graphs resolve components with buoyant-density differences of 0.001 g/cm3 in equilibrium density gradients

A method derived from DNA melting-curve analysis has been modified for determining homogeneity of DNA species centrifuged to equilibrium in a CsCl gradient. DNA species of known density were purified, centrifuged to equilibrium in a Spinco Model E analytical ultracentrifuge, and analyzed by probability distribution. In order to determine the limits of resolution by this procedure, samples with varying buoyant-density separations were obtained by mixing different DNA species. Results indicate this method can detect overlapping mixtures of DNA in relative amounts of 9:1 and resolve two species of DNA of equal concentrations with a buoyant-density separation of 0.001 g/cm³.     

Some features of imaging of the processes occurring in an extended arc discharge in atmospheric-pressure air

Processes occurring in the low-temperature plasma of extended quasi-stationary arc discharges in air between graphite electrodes are investigated. Along with the conventional (constricted) discharge geometry, other discharge modes—diffuse (distributed) and diffuse-constricted—are studied. Contraction, stratification, and shunting processes are considered. Current oscillation modes are revealed that are caused by the interaction between the cathode and anode jets and the origination of plasma jets and solid particles from the locally overheated anode surface. 1 The use of graphite electrodes with standard atmospheric pressure excludes the presence of the liquid phase in the electrode spots     

Study of the homogeneity of the current distribution in a dielectric barrier discharge in air by means of a segmented electrode

The current distribution in a dielectric barrier discharge in atmospheric-pressure air at a natural humidity of 40–60% was studied experimentally with a time resolution of 200 ps. The experimental results are interpreted by means of numerically simulating the discharge electric circuit. The obtained results indicate that the discharge operating in the volumetric mode develops simultaneously over the entire transverse cross section of the discharge gap.     

Cytogenetic effects produced by an in vitro exposure of human lymphocytes to ultrasounds with intensity levels of 1 W/cm2 to 3 W/cm2

Peripheral blood from four human male donors have been exposed to ultrasounds delivered at intensity levels of 1, 2 or 3 W/cm2. Cytogenetic observations performed after in vitro culture of blood samples in Ham's medium did not reveal a significant increase of structural chromosome aberrations nor of sister chromatid exchanges in the lymphocytes.     

Investigation of the barrier discharge structure near the electrode with a cylindrical cross section

The approximate analytical correlations allowing for the investigation of the effect of different geometrical and physical parameters on the barrier discharge evolution near the electrode with a cylindrical cross section are obtained. The found correlations make it possible to estimate the time of the barrier discharge existence. New essential peculiarities of the barrier discharge evolution are revealed and verified.     

Measurements of the electron density and degree of plasma ionization in a plasma target based on a linear electric discharge in hydrogen

Laser interferometry methods were used to measure the density of free electrons and degree of plasma ionization in a hydrogen target intended for experiments on determining energy losses of heavy ion beams in an ionized matter. It is shown that the linear electron density can be varied in the range from 3.3 × 10¹⁷ to 1.3 × 10¹⁸ cm^?2 by varying the initial plasma parameters (the hydrogen pressure in the target and the discharge current). The error in measuring the linear electron density in the entire range of the varied plasma parameters was less than 1%. The maximum degree of plasma ionization achieved at the initial gas pressure of 1 mbar was 0.62 ± 0.05.     

3D Stationary electric current density in a spherical tumor treated with low direct current: an analytical solution

Electrotherapy with direct current delivered through implanted electrodes is used for local control of solid tumors in both preclinical and clinical studies. The aim of this research is to develop a solution method for obtaining a three-dimensional analytical expression for potential and electric current density as functions of direct electric current intensity, differences in conductivities between the tumor and the surrounding healthy tissue, and length, number and polarity of electrodes. The influence of these parameters on electric current density in both media is analyzed. The results show that the electric current density in the tumor is higher than that in the surrounding healthy tissue for any value of these parameters. The conclusion is that the solution method presented in this study is of practical interest because it provides, in a few minutes, a convenient way to visualize in 3D the electric current densities generated by a radial electrode array by means of the adequate selection of direct current intensity, length, number, and polarity of electrodes, and the difference in conductivity between the solid tumor and its surrounding healthy tissue.     

Structure of a discharge induced by a coaxial microwave plasmatron with a gas-supply channel in the inner electrode

The structure of a discharge induced by a coaxial microwave plasmatron with a gas-supply channel in the inner electrode of a coaxial waveguide is investigated. A plasmatron with a power of up to 10 W operates at a frequency of 10 GHz. Depending on the operation regime, the discharge takes either a filament or torch form. A plasma filament arises at low flow rates of the working gas (argon) and occurs at the border of the potential core of the gas jet. A torch discharge occurs at high flow rates and has the form of a hollow cone. In both cases, the discharge arises in the potential core of the gas jet and does not spread beyond it. The distribution of the microwave field in the discharge plasma is determined.     

Gas temperature in the plasma of a low-pressure electrode microwave discharge in hydrogen

The gas temperature in an electrode microwave discharge in hydrogen at pressures of 1–8 torr and input powers of 20–90 W is determined from the relative intensities of the rotational lines of the electronically excited molecules of the Fulcher α system of molecular hydrogen. It is found that the gas temperature in the discharge is no higher than 800 K over the entire range of the experimental conditions under study. For this reason, plasma resonance cannot be regarded as a factor determining the physical processes in the discharge over the entire pressure range. Since the discharge unit is a nonuniform gas-dynamic system (the gas is fed through a small hole into a chamber of limited size), there is a possibility of generating vortex flows that intensively mix the gas. This results in a uniform distribution of the gas temperature throughout the entire volume of the spherical plasma structure produced in the experiment.     

Activation of a TRPC3-dependent cation current through the neurotrophin BDNF

Nonvoltage-gated cation currents, which are activated following stimulation of phospholipase C (PLC), appear to be major modes for Ca2+ and Na+ entry in mammalian cells. The TRPC channels may mediate some of these conductances since their expression in vitro leads to PLC-dependent cation influx. We found that the TRPC3 protein was highly enriched in neurons of the central nervous system (CNS). The temporal and spatial distribution of TRPC3 paralleled that of the neurotrophin receptor TrkB. Activation of TrkB by brain-derived nerve growth factor (BDNF) led to production of a PLC-dependent, nonselective cation conductance in pontine neurons. Evidence is provided that TRPC3 contributes to this current in vivo. Thus, activation of TrkB and PLC leads to a TRPC3-dependent cation influx in CNS neurons.     

Determination of the electron density and electric field in the plasma of a low-pressure microwave electrode discharge in hydrogen from the measured spectral line intensities

The parameters of the plasma of a microwave electrode discharge in hydrogen at pressures of 1–8 torr and incident powers of 20–80 W are measured by the so-called “relative intensity” method. The method allows one to determine the electron density and electric field in plasma by measuring the relative intensities of the H_α, H_β, and 763.5-nm Ar line emission and calculating the electron-impact rate constants from the homogeneous Boltzmann equation. The measurements show that there are regions in the discharge where the electron density is higher (a bright electrode sheath) and lower (a spherical region) than the critical density for the frequency 2.45 GHz (n_cr～7×10¹⁰ cm^?3). Inside the spherical region, the electric field varies slightly over the radius and the electron density increases as the discharge boundary is approached. The observed discharge structure can be attributed to the presence of a self-sustained discharge zone (electrode sheath); a non-self-sustained discharge zone (spherical region); and a decaying plasma region, which is separated from the active discharge zone by an electric double layer.     

Dynamics of the water molecule density in a discharge chamber filled with a low-pressure humid gas

The dynamics of the H₂O molecule density in a metal gas-discharge chamber filled with low-pressure water vapor or its mixtures with noble gases was investigated by manometric and spectral methods. Regimes both with and without discharge excitation were studied. In the absence of a discharge, the molecule density dynamics is governed by the heterogeneous interaction of molecules with the chamber walls. In the presence of a discharge, in addition to the heterogeneous interaction, fast plasmachemical molecule dissociation also contributes to the initial stage of H₂O molecule loss. The role of heating of the chamber walls is discussed.     

The density of the extinction probability of a time homogeneous linear birth and death process under the influence of randomly occurring disasters

Under the influence of randomly occurring disasters, the eventual extinction probability, q, of a birth and death process, Z, is a random variable. In this paper, we obtain an integral expression for the probability density function g(x) of q under the assumption that the population process Z is a time homogeneous linear birth and death process and the disasters occur according to an arbitrary renewal process so that its interarrival times have a density. An example is provided to demonstrate how to evaluate the integral numerically.     

Low-current medium-pressure RF discharge with electron photoemission in the electrode sheath and penetration of the sheath electrons into the discharge column

A model is developed for simulating a low-current moderate-pressure RF discharge with allowance for such characteristic discharge properties as the existence of two sheaths near both electrodes throughout the RF field period; the formation of an electron cloud at the sheath boundary that periodically fills the sheath and leaves it, depending on the phase of the applied RF voltage; the production by the sheath electrons of metastable gas particles that interact with the cloud electrons during subsequent field periods, followed by the excitation of metastable states to the emitting levels; the formation of a sheath in a low-current RF discharge due to the overlap of the secondary electron avalanches triggered by electron photoemission from the electrode surface; and the conditions under which the sheath electrons penetrate into the positive column and accumulate there, which makes, thereby making a low-current RF discharge similar to a non-self-sustained discharge. The parameters of the sheath in a low-current RF discharge are determined by the conditions under which the electron photoemission current from the electrode surface in the sheath is self-sustaining and, like the parameters of the positive discharge column, depend on the sort of gas, the gas pressure, the frequency of the applied RF field, and the interelectrode distance. The results of calculating the parameters of the sheath and column of a low-current RF discharge for nitrogen and helium at different pressures, as well as for different field frequencies and interelectrode distances, are presented and are compared with the experimental data.     

On the current density in a high-current plasma-filled diode with an explosive emission cathode

Based on the analysis of the available data from experimental studies and numerical simulations of high-current plasma-filled diodes, it is shown that the fast (～2 cm/μs) motion of the explosive emission cathode plasma does not allow the double layer in which the high-current electron beam forms to reach a steady (or quasi-steady) state. As a result, the double layer turns out to be substantially thinner than a steady-state one and the current density in it is substantially higher. The proposed hypothesis explains well the excess of the observed current density over its calculated (stationary) value.     

Dynamics of the structure of the plasma current sheath in a plasma focus discharge

The study is aimed at investigating the fine structure of the plasma current sheath (PCS) in the PF-3 plasma focus facility. The PCS dynamics in a deuterium discharge was studied. The PCS parameters were measured using absolutely calibrated magnetic probes installed at different positions with respect to the facility axis and the anode surface. A magneto-optical probe recording both the magnetic signal and the PCS optical luminosity was first applied to analyze the PCS structure. This made it possible to spatially resolve the current and shock-wave regions. It is demonstrated that the current distribution is different in different discharge stages. It is shown that the neutron yield is determined by the value of the current compressed toward the axis, rather then the amplitude of the total discharge current.     

Ecton processes in the generation of pulsed runaway electron beams in a gas discharge

As was shown earlier for pulsed discharges that occur in electric fields rising with extremely high rates (10¹⁸ V/(cm s)) during the pulse rise time, the electron current in a vacuum discharge is lower than the current of runaway electrons in an atmospheric air discharge in a 1-cm-long gap. In this paper, this is explained by that the field emission current from cathode microprotrusions in a gas discharge is enhanced due to gas ionization. This hastens the initiation of explosive electron emission, which occurs within 10^–11 s at a current density of up to 10¹⁰ A/cm². Thereafter, a first-type cathode spot starts forming. The temperature of the cathode spot decreases due to heat conduction, and the explosive emission current ceases. Thus, the runaway electron current pulse is similar in nature to the ecton phenomenon in a vacuum discharge.