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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]

Dependences of kinetic and transport coefficients of electrons in helium on the electric field strength E reduced to the atomic concentration N in the E/N range from 15 to 1000 of Td are calculated using the earlier developed Monte-Carlo code. The calculation results are compared to the published experimental data. It is shown that for the available experiments, significant inaccuracy is inherent in the range of high E/N magnitudes caused by electrons not being in equilibrium with the field in strong fields. It is shown that the diffusion–drift approximation for the space–time evolution of electron concentration in helium is not applicable above E/N ≈ 200 Td. The gas gain G of helium-filled proportional counter is calculated; the computed G magnitudes agree well with the measurement data. The discrepancy between the measured G values and previously published calculated G values is explained. [ABSTRACT FROM AUTHOR]

Electrical conductivity in a laser beam channel has been investigated. Oscillations of the conductivity caused by the oscillation motion of electrons in laser-induced breakdown plasma are established in an external electric field. An expression for estimation of charged particle concentration has been obtained. [ABSTRACT FROM AUTHOR]

An analysis of the integral Boltzmann equation to determine the electron distribution function in a weak electric field and its solution are presented. The solution based on a simple model of electron collisions with neutral particles of a gas is compared with the well-known solution of the corresponding approximate differential Fokker–Planck equation. The essential difference between the two approaches is manifested in the behavior of the electron distribution function at electron velocities comparable with the thermal velocity of the atoms of the gas. As a result of the calculations carried out, kernels of the integral Boltzmann equations necessary for solving similar problems of physical kinetics and others have been determined within the model of collisions accepted. [ABSTRACT FROM AUTHOR]

A modified Ohm's Law, derived from the conservation of deuterium and carbon ions and electron momentum and the requirement for charge neutrality, yields an expression for the radial electric field, Er, in the edge pedestal region in terms of the motional electric field due to the carbon and deuterium ion rotation velocities as well as pressure gradients and the radial plasma current. This analytical Ohm's Law model for Er is first shown to be consistent with the conventional "experimental" electric field calculated from the carbon radial momentum balance using experimental carbon rotation and pressure gradient measurements when experimental profiles are used to evaluate the Ohm's Law in three DIII-D [Luxon, Nucl. Fusion 42, 614 (2002)] representative discharges (for L-mode, H-mode, and Resonant Magnetic Perturbation operating regimes). In order to test the practical predictive ability of the modified Ohm's Law, the calculations were repeated using rotation velocities calculated with neoclassical rotation models instead of measured rotation velocities. The Ohm's Law predicted Er using theoretical rotation velocities did not agree with the "experimental" Er as well as the Ohm's Law prediction using experimental rotation velocities, indicating that more accurate models for predicting edge rotation velocity are needed in order to have a validated predictive model of Er in the plasma edge. [ABSTRACT FROM AUTHOR]

In the present work, results of investigations into the dynamics of secondary electrons with helium atoms in the presence of the reverse electric field arising in the flare of a high-voltage pulsed beamtype discharge and leading to degradation of the primary electron beam are presented. The electric field in the discharge of this type at moderate pressures can reach several hundred V/cm and leads to considerable changes in the kinetics of secondary electrons created in the process of propagation of the electron beam generated in the accelerating gap with a grid anode. Moving in the accelerating electric field toward the anode, secondary electrons create the so-called compensating current to the anode. The character of electron motion and the compensating current itself are determined by the ratio of the field strength to the concentration of atoms (E/n). The energy and angular spectra of secondary electrons are calculated by the Monte Carlo method for different ratios E/n of the electric field strength to the helium atom concentration. The motion of secondary electrons with threshold energy is studied for inelastic collisions of helium atoms and differential analysis is carried out of the collisional processes causing energy losses of electrons in helium for different E/n values. The mechanism of creation and accumulation of slow electrons as a result of inelastic collisions of secondary electrons with helium atoms and selective population of metastable states of helium atoms is considered. It is demonstrated that in a wide range of E/n values the motion of secondary electrons in the beam-type discharge flare has the character of drift. At E/n values characteristic for the discharge of the given type, the drift velocity of these electrons is calculated and compared with the available experimental data. [ABSTRACT FROM AUTHOR]

This paper presents research results on the ion charge state and energy distribution in the anode plasma generated at the spark stage of a high-current vacuum discharge. The cathode and the anode are both made of liquid metal Ga–In alloy. The use of a circuit with a relatively low impedance (6 \Omega) and a small interelectrode gap (\sim1~mm) made it possible to obtain a relatively high discharge current (\sim1~kA) at an initial voltage of 10–15 kV. Therefore, an electron beam consisting of a train of pulses with a duration of 5 ns and power density of \sim2.5\cdot 10^8~W/cm^2 is formed in \sim50~ns, giving rise to high-density anode ablation plasma. The parameters of the ion component of this plasma are investigated with a mass energy analyzer. It is found that ions with Z=1\--4 are present in the plasma, and the ion energy increases roughly in proportion with increasing ion charge. Increasing the initial voltage causes an increase in the fraction of highly charged ions and in their energy. The absolute values of the ion energy reach \sim1~keV. Two mechanisms of ion acceleration are discussed: adiabatic expansion of the anode plasma and ion acceleration by an ambipolar electric field. It is shown that the regularities found in this paper can be explained only with resort to both mechanisms. [ABSTRACT FROM AUTHOR]

We report on model studies of stimulated L → H transitions [K. Miki et al., Phys. Rev. Lett. 110, 195002 (2013)]. These studies use a reduced mesoscale model. Model studies reveal that L → H transition can be triggered by particle injection into a subcritical state (i.e., PThresh). Particle injection changes edge mean flow shear via changes of density and temperature gradients. The change of edge mean flow shear is critical to turbulence collapse and the subsequent stimulated transition. For low ambient heating, strong injection is predicted to trigger a transient turbulence collapse. Repetitive injection at a period less than the lifetime of the collapsed state can thus maintain the turbulence collapse and so sustain a driven H-mode-like state. The total number of particles required to induce a transition by either injection or gas puffing is estimated. Results indicate that the total number of injected particles required is much smaller than that required for a transition by gas puffing. We thus show that internal injection is more efficient than gas puffing of comparable strength. We also observe that zonal flows do not play a critical role in stimulated transitions. For spontaneous transitions, the spike of the Reynolds work of turbulence on the zonal flow precedes the spike in the mean electric field shear. In contrast, we show that the two are coincident for stimulated transitions, suggesting that there is no causal link between zonal and mean flows for stimulated transitions. [ABSTRACT FROM AUTHOR]

Experimental results on the generation and maintenance of the toroidal current in the Globus-M spherical tokamak by using waves in the lower hybrid frequency range without applying an inductive vortex electric field are presented. For this purpose, the original ridge guide antennas forming a field distribution similar to that produced by multiwaveguide grills were used. The high-frequency field (900 MHz) was used for both plasma generation and current drive. The magnitude of the generated current reached 21 kA, and its direction depended on the direction of the vertical magnetic field. Analysis of the experimental results indicates that the major fraction of the current is carried by the suprathermal electron beam. [ABSTRACT FROM AUTHOR]

An expression is derived for the electric field strength near a wet hailstone in an approximation quadratic in the oscillation amplitude of a charged liquid layer on its surface. It is found that the electric field strength in a small neighborhood of the capillary wave crests grows with the number of a mode governing the initial deformation of the equilibrium (spherical) shape of the liquid layer. Even if the charge is small (when the Rayleigh parameter of the hailstone equals one-hundredth of the value critical for stability against the self-charge), the electric field near the hailstone is high enough for initiating a corona discharge in its vicinity. [ABSTRACT FROM AUTHOR]

Results are presented from experiments on the acceleration of electrons by a 2.45-GHz microwave field in an adiabatic mirror trap under electron cyclotron resonance conditions, the electric and wave vectors of the wave being orthogonal to the trap axis. At a microwave electric field of ≥10 V/cm and air pressures of 10−6–10−4 Torr (the experiments were also performed with helium and argon), a self-sustained discharge was initiated in which a fraction of plasma electrons were accelerated to energies of 0.3–0.5 MeV. After the onset of instability, the acceleration terminated; the plasma decayed; and the accelerated electrons escaped toward the chamber wall, causing the generation of X-ray emission. Estimates show that electrons can be accelerated to the above energies only in the regime of self-phased interaction with the microwave field, provided that the electrons with a relativistically increased mass penetrate into the region with a higher magnetic field. It is shown that the negative-mass instability also can contribute to electron acceleration. The dynamic friction of the fast electrons by neutral particles in the drift space between the resonance zones does not suppress electron acceleration, so the electrons pass into a runaway regime. Since the air molecules excited by relativistic runaway electrons radiate primarily in the red spectral region, this experiment can be considered as a model of high-altitude atmospheric discharges, known as “red sprites.” [ABSTRACT FROM AUTHOR]

Measurements of plasma flow damping have been made in the Helically Symmetric eXperiment [F. S. B. Anderson, A. F. Almagri, D. T. Anderson, P. G. Mathews, J. N. Talmadge, and J. L. Shohet, Fusion Technology 27, 273 (1995)] using a biased electrode to impulsively spin the plasma and Mach probes to measure the rotation. There is a distinct asymmetry between the spin-up when the bias is initiated and relaxation when the electrode current is broken. In each case, two time-scales are observed in the evolution of the plasma flow. These observations motivate the development of new neoclassical modeling techniques, including a new model where the fast increment of the electric field initiates the spin-up process. The flow in the quasisymmetric configuration rises more slowly and to a higher value than in a configuration with the quasisymmetry broken, and the rise time-scale is in reasonable agreement with the neoclassical spin-up model. The flows decay more slowly in the quasisymmetry configuration than in the configuration with the quasisymmetry broken, although the decay rates are significantly faster than the neoclassical prediction. [ABSTRACT FROM AUTHOR]

The influence of low electric fields on the average electron energy in an afterglow krypton plasma is studied by means of probe diagnostics and theoretical analysis. It is shown that, when the average electron energy is lower than the energy corresponding to the minimum scattering transport cross section, the degree of plasma ionization substantially affects the shape of the electron energy distribution function (EEDF). The nonequlibrium character of the EEDF results in the density dependence of the coefficient of ambipolar diffusion, which leads to a change in the radial profile of the charged particle density, an increase in the drop in the ambipolar potential across the plasma, and an increase in the rate of diffusive plasma decay. These effects substantially enhance the diffusive cooling of electrons, which is probably a decisive factor influencing the electron energy balance in high-Z noble gases. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The critical electric field at which the ionization rate is equal to the rate of electron attachment to neutral particles in heated sulfur hexafluoride (SF[sub 6]) is calculated by numerically solving the Boltzmann equation for electrons. It is shown that the main causes of a decrease in the critical field with increasing gas temperature are the change in the electron energy distribution due to gas dissociation and the reduction in the rate of electron attachment to neutral particles. The calculated results are in qualitative agreement with the available experimental data. © 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The biasing experiments and the problem of the effective perpendicular conductivity in a tokamak are studied both analytically and numerically. The simulations were performed by means of the B2SOLPS5.0 transport code [V. A. Rozhansky et al., Nucl. Fusion 41, 387 (2001)] where the fluid set of equations is solved for the real divertor geometry. It is demonstrated that there exist three regimes, which correspond to the different values of the effective perpendicular conductivity and to different profiles of the radial electric field and toroidal and poloidal rotations. Simulation results are compared with existing and developed analytical models. [ABSTRACT FROM AUTHOR]

The electron energy distribution function in an afterglow molecular nitrogen plasma is studied both experimentally and theoretically under the conditions of weak electric fields such that the electron gas is heated by superelastic collisions of electrons with vibrationally excited molecules. Based on the mean electron energy balance, it is established that, depending on the degree of plasma ionization and the vibrational temperature of nitrogen molecules, an afterglow plasma may evolve into two states, differing in electron temperature. This kind of bistability is found to stem from the difference in the main mechanisms for electron energy losses in the two stable states. The prediction that the shape of the electron energy distribution function should change in a jumplike manner when a weak electric field is imposed has been confirmed experimentally. © 2001 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

In guiding-center simulations of a tokamak plasma edge, bifurcations of both the radial electric field and the electrode current are observed for a threshold value of the electrode bias voltage, in qualitative agreement with experiments. The simulations are neoclassical and Monte Carlo based, also containing the perpendicular viscosity effect. Above the voltage threshold, an inward moving, solitary radial electric field structure is generated with a concomitant drop in the electrode current. The position, width, and height of the soliton depend on the magnitude and radial variation of the conductivity (and, thus, on local plasma parameters), finite orbit effects, and also on the perpendicular viscosity and neutral density. The obtained E[sub r] structures are narrower and higher than the ones measured in the edge polarization experiments in the Ju¨lich tokamak TEXTOR-94 [S. Jachmich et al., Plasma Phys. Controlled Fusion 40, 1105 (1998)]. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A study is made of physical effects that accompany the convergence of the pinch constriction and are caused by vortex electric fields generated in the constriction cavity. © 2000 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Examines the improvement of the Ohmic confinement phase during the turbulent heating pulse in the Hefei Tokamak-6M. Factor affecting the steepness of the electron temperature and density profiles; Role of the radial electric field during the transition of L mode and H mode; Effect of radial electric field on the suppression of the plasma potential fluctuation.

Reports on the radial electric field inside a separatrix that has been deduced from spectroscopic measurements of impurities on Tokamak de Varennes, using the reduced radial momentum balance and two neoclassical models. Role of electric fields in the confinement of both particles and energy.

Studies the effects of radial electric field on charged particle motion and transport in the toroidal magnetic system. Effects of radial electric field on particle orbits; Ion radial mobility due to the combined effects of radial electric field and charge exchange collisions; Formation of a transport barrier near the tokamak plasma edge.

Focuses on the generation of the edge radial electric field and corresponding plasma rotation for toroidal confinement systems with a separatrix configuration of magnetic surfaces. Use of the classical acceleration of plasma by ion orbital losses to explain electric field and plasma rotation observed near walls when plasma flow to the neutralizing wall is included.

Turbulence in Scrape-off layer (SOL) of tokamak plasma has been studied numerically using interchange modes with the help of electron continuity, quasineutrality, and ion energy equations. Electron temperature is assumed uniform. We have studied dynamics of seeded plasma blob and plasma turbulence to identify the role of ion temperature and its gradient. The ion temperature elongates the blob poloidally and reduces its radial velocity. Initial dipole nature of the plasma blob potential breaks and generates few more dipoles during its propagation in the SOL. Plasma turbulence simulation shows poloidally elongated density and ion temperature structures that are similar to the seeded blob simulation studies. Fluctuations of the density and ion temperature have been presented as function of scale lengths of the density and ion temperature. Reduction of the SOL width and increase of radial electric field have been measured in the presence of the ion temperature. Particle and energy transports have been also presented as the function of the density and ion temperature scale lengths. [ABSTRACT FROM AUTHOR]