A powerful electrohydrodynamic flow generated by a high-frequency dielectric barrier discharge in a gas

Theoretical and experimental studies of an electrohydrodynamic flow induced by a high-frequency dielectric barrier discharge distributed over a dielectric surface in a gas have been conducted. Dependences of the ion current, the gas flow velocity, and the spatial distributions thereof on the parameters of the power supply of the plasma ion emitter and an external electric field determined by the collector grid voltage have been described.     

Optical characteristics and parameters of gas-discharge plasma in a mixture of mercury dibromide vapor with neon

Results are presented from studies of the optical characteristics and parameters of plasma of a dielectric barrier discharge in a mixture of mercury dibromide vapor with neon—the working medium of a non-coaxial exciplex gas-discharge emitter. The electron energy distribution function, the transport characteristics, the specific power losses for electron processes, the electron density and temperature, and the rate constants for the processes of elastic and inelastic electron scattering by the working mixture components are determined as functions of the reduced electric field. The rate constant of the process leading to the formation of exciplex mercury monobromide molecules is found to be 1.6 × 10^?14 m³/s for a reduced electric field of E/N = 15 Td, at which the maximum emission intensity in the blue-green spectral region (λ_max = 502 nm) was observed in this experiment.     

Analytic approximations for describing the interactionof charged particles with the emitter of a radioisotope current source

Approximate formulas for the modeling of the interaction of fast alpha particles and suprathermal electrons with solid-state plasmas of the emitter films in a secondary-electron-emission radioisotope current source are derived. The approximate formulas are used to estimate the characteristic interaction parameters, in particular, the effective stopping power of the composite material of the emitter, the ranges of alpha particles, the optimum thickness of the emitter, and the maximum possible number of binary current cells. The results obtained can be used to optimize the parameters of a prototype model of such a source and to analyze its current-voltage characteristic. They can also be applied in Monte Carlo modeling of the generation of suprathermal electrons by fast ion fluxes in a solid-state plasma and ion flux-induced fast nonequilibrium secondary electron emission from metallic and dielectric films.     

Energy efficiency of electron plasma emitters

Electron emission influence from gas-discharge plasma on plasma emitter energy parameters is considered. It is shown, that electron emission from plasma is accompanied by energy contribution redistribution in the gas-discharge from plasma emitter supplies sources—the gas-discharge power supply and the accelerating voltage power supply. Some modes of electron emission as a result can be realized: “a probe measurements mode,” “a transitive mode,” and “a full switching mode.”     

On thermofield electron emission from metal microtips

The electric field in the vicinity of a cone apex has an integrable singularity. Therefore, in order to calculate the thermofield emission current from a conical tip, it is necessary to find the emission current density at extremely high electric fields at the cone apex. In this paper, an original method for correctly calculating the electric field near a perfect conical tip and a tip with a rounded apex is proposed. A universal numerical approach to calculating thermionic, field, and thermofield electron emission from metal in a wide range of surface electric fields is offered. It is shown that, at high electric fields, the thermofield current density tends to a certain limiting (saturated) value, and the reason for this saturation is revealed. It is found that, for moderate fields, the total electron emission current from a conical tip is determined by the current from the immediate vicinity of the apex and depends substantially on the curvature radius of its rounding.     

Modelling the effects of hydrogen passivation and strain on the field emission from armchair-graphene nanoribbon using a modified non-equilibrium Green’s function method

In this report, we introduced a modified non-equilibrium Green’s function method to investigate the structural effects on the field emission current from an armchair graphene nanoribbon. We introduce a modified self-energy which is useful to study the effects of potential barrier in the field emission devices. Investigation into the effects of hydrogen passivation and applied strain can be realised using our modified formalism. Also a practical method to consider the effect of device parameters, such as channel length, anode–cathode separation and gate potential can be provided by the proposed formalism. The quantum effects of the emitter’s structure on the field emission are achievable by our introduced method.     

Means for efficient electron beam generation in wide-aperture open-discharge light sources

The interaction of a plasma in the accelerating gap of an open discharge with a strong external electric field and with the cathode surface has been investigated theoretically and experimentally. In a pulsed nanosecond discharge, the ion inertia and plasma screening of the electric field cause a fast growth of the electric field E in the cathode region and a decrease in the length of the latter. Along with a reduction of the electron multiplication factor at high electric fields, this leads to a substantial decrease in the ion flux toward the cathode, which allows one to develop highly efficient open-discharge light sources with a long lifetime and low cathode sputtering. In this respect, continuous and quasi-continuous discharges are less advantageous because of the smaller increase in the electric field in the cathode region. The Townsend coefficients of charge multiplication and electron emission at high electric fields typical of open discharges have been measured for the first time. Fast ions and atoms extracted from the plasma of the accelerating gap significantly affect the cathode emission properties. In particular, photoemission is enhanced by more than one order of magnitude and becomes the main mechanism for electron generation. This also increases the efficiency and lifetime of open-discharge light sources.     

Boundary conditions on the plasma emitter surface in the presence of a particle counter flow: I. Ion emitter

Emission of positively charged ions from a plasma emitter irradiated by a counterpropagating electron beam is studied theoretically. A bipolar diode with a plasma emitter in which the ion temperature is lower than the electron temperature and the counter electron flow is extracted from the ion collector is calculated in the one-dimensional model. An analog of Bohm’s criterion for ion emission in the presence of a counterpropagating electron beam is derived. The limiting density of the counterpropagating beam in a bipolar diode operating in the space-charge-limited-emission regime is calculated. The full set of boundary conditions on the plasma emitter surface that are required for operation of the high-current optics module in numerical codes used to simulate charged particle sources is formulated.     

Theory of the near-wall conductivity

A model describing the phenomenon of the electron current in a plane plasma slab bounded by parallel dielectric walls in the presence of a homogeneous magnetic field perpendicular to the walls and an electric field oriented along the walls is presented. The current flows along the electric field because of the electron collisions with diffusely scattering walls. The model takes into account the presence of Debye layers and the non-Maxwellian character of the electron distribution function. Collisions in the plasma volume are ignored.     

Numerical Investigation of the Instability-Based Power Emission from an Ungated Plasmonic HEMT Using Complete Hydrodynamic Model

The full-wave analysis of the Dyakonov–Shur instability in an ungated short-channel high electron mobility transistor (HEMT) is investigated in this paper. This mechanism causes the emission of electromagnetic radiations by the device. The accurate analysis of the device is important especially when large electric fields are present. Herein, to analyze such structures, the complete hydrodynamic model, which is the simultaneous solution of Maxwell’s equations and the first three moments of the Boltzmann transport equation, is used. This model well describes the electron-wave interactions by considering the transport parameter variations with the electron energy and temperature. These variations are especially considerable when the emitter operates at high electromagnetic fields and were not considered in previous studies. The obtained results demonstrate the oscillation current along the channel and consequently the radiated power of the device are severely influenced by the transport parameter variations. The developed analysis method describes the behavior of the device as a terahertz emitter more accurately than the available ones.

     

Assessment of exposure to intermediate frequency electric fields and contact currents from a plasma ball

While electric fields at intermediate frequencies are not widely utilized for industrial technologies, surprisingly, certain toys emit the highest electric fields found in our living environment. These toys, plasma balls, are devices that use high voltage to create ionized light discharges. In this study, we assessed exposure to electric fields and contact/induced current from a recreational plasma ball device. The electric field strength was measured as a function of distance from the device, and the contact/induced current was measured with a current clamp in different exposure situations with point or grasping contact. The characteristic spectra of the electric field and contact current were measured, and both the multiple frequency rule and weighting of the spectra were applied according to the International Commission on Non-Ionizing Radiation Protection (ICNIRP) 1998 and 2010 guidelines. The results indicate that the recommended reference levels for the general public are exceeded at distances <1.2 m, and that the contact currents in the hand may be twice higher than recommended by the general public guidelines.     

A model of the electric field of the brain at EEG and microwave frequencies

A simple calculation of the current dipole moment of the extracellular electric field of the cortex is proposed; it is based on the dipole layer model. The model is extended to the range of microwave frequencies. Arguments in favor of emission of microwave radiation by the dendritic membranes of pyramidal neurons are presented and the strength of the radiative electric field at a distance from the head is calculated and discussed.     

Radial electric field during dynamic processes in a tokamak and L-H transitions

Expressions for the radial electric field in tokamaks are derived with allowance for an additional contribution of the longitudinal electron viscosity (or the associated Ware drift). It is shown that, in transient processes during which the toroidal electric field at the plasma edge increases, the additional electric field can become rather strong. An increase in the shear of the poloidal plasma rotation can trigger the L-H transition. That the experimentally observed transitions to an improved confinement mode can be ascribed to this effect is illustrated by simulating discharges in the current ramp-up experiments in the Tuman-3M tokamak.     

Simulation of electron beam formation and transport in a gas-filled electron-optical system with a plasma emitter

The results of computer simulations of the electron-optical system of an electron gun with a plasma emitter are presented. The simulations are performed using the KOBRA3-INP, XOOPIC, and ANSYS codes. The results describe the electron beam formation and transport. The electron trajectories are analyzed. The mechanisms of gas influence on the energy inhomogeneity of the beam and its current in the regions of beam primary formation, acceleration, and transport are described. Recommendations for optimizing the electron-optical system with a plasma emitter are presented.     

Ion acceleration in a dipole vortex in a laser plasma corona

Particle-in-cell simulations show that the inhomogeneity scale of the plasma produced in the interaction of high-power laser radiation with gas targets is of fundamental importance for ion acceleration. In a plasma slab with sharp boundaries, the quasistatic magnetic field and the associated electron vortex structure produced by fast electron beams both expand along the slab boundary in a direction perpendicular to the plasma density gradient, forming an extended region with a quasistatic electric field, in which the ions are accelerated. In a plasma with a smooth density distribution, the dipole magnetic field can propagate toward the lower plasma density in the propagation direction of the laser pulse. In this case, the electron density in an electric current filament at the axis of the magnetic dipole decreases to values at which the charge quasineutrality condition fails to hold. In electric fields generated by this process, the ions are accelerated to energies substantially higher than those characteristic of plasma configurations with sharp boundaries.     

Two-Dimensional Simulation of a Plasma Electron Emitter by PIC-Code

Plasma Physics Reports - In a two-dimensional plane-parallel geometry, the particle-in-cell method was used to numerically simulate a plasma electron emitter with a slit emission aperture. The...     

Three-dimensional MHD simulations of forced magnetic reconnection

Results are presented from MHD simulations of three-dimensional flows of a high-conductivity plasma in the vicinity of a null point of a magnetic field. The excitation of an electric current at the boundary of the computation region results in self-consistent plasma flows and change in the structure of the magnetic field. Generally, in the vicinity of a null point, an MHD singularity arises that manifests itself in the formation of locally plane current sheets. It is shown that the current sheet can be oriented either along the separatrix surface of a magnetic configuration or perpendicular to it, except for axisymmetric configurations (or close to them), when the excitation of an electric current in the direction orthogonal to the separatrix surface does not lead to the formation of a current sheet.     

Spatial and temporal electroselection patterns in electric field stimulation of polarized luminescence from photosynthetic membrane vesicles

Electroselection processes of charge recombination are manifested in the study of electric field induced polarized emission from photosynthetic membrane vesicles. The study explores the coupled spatial-temporal characteristics of electric field induced charge recombination by examining the dependence of the integrated polarized emission and the time dependent polarization on electric field strength. The experimental results were fitted to theoretical models by computer simulations employing empirical parameters. Simulation of the dependence of the integrated polarized components of emission on electric field strength, suggests field-dependent increased ratio between radiative and nonradiative rates of charge recombination. The observation that the initial polarization values are independent of electric field strength supports the assumption that electric field induced emission originates from the pole area and then spreads away from it towards the equator. The propagation rate of this electric field induced charge recombination from the pole area towards the equator is reflected by the decay of polarization which increases upon raising the electric field strength. Simulation of the polarization's decay, based on a calculated angle of 26.3 ± 0.4° between the transition moment of emission and the plane of the membrane, establishes coupled temporal spatial patterns of electroselection in intramembrane electron transfer invoked by exposing preilluminated photosynthetic vesicles to a homogeneous electric field.     

Demidov-Elagin-Fanchenko effect

It is shown how the plateau that has been revealed earlier in the nonlinear dependence of the experimentally studied electrical conductivity of a turbulent plasma on the electric field strength can be understood by taking into account the turbulent Joule heating of the plasma electrons. A new, experimentally possible physical pattern of the penetration of a quasistatic vortex electric field into a turbulent plasma is revealed that is attributed to the time dependence of the anomalous turbulent conductivity or, more generally, to the temporally nonlocal relationship between the current density and the electric field strength due to turbulent heating.