A positive column of electric discharge in a transverse magnetic field

The influence of a transverse magnetic field on the characteristics of the positive column of electric discharge was investigated in both the diffusion and nondiffusion approximations. All solutions in the diffusion approximation were derived in analytical form. It is shown that with the enhancement of the magnetic field induction, the concentration distributions of the plasma and particle fluxes to insulated walls become nonsymmetric, the concentration maximum displaces in the direction of the magnetic force action, and the ion flux concurrent with this force may exceed substantially the ion flux in the opposite direction. The dependences of discharge parameters on the induction value are defined for helium. It is demonstrated that there is a maximum value of induction which bounds from above the range of magnetic fields, where the stationary state of the positive column is possible. In the range allowed for the stationary state, a single induction value is matched by two different modes of the positive column varying in values of the electron energy, drift speed, and electric-field strength. By means of the transverse magnetic field, it is possible to vary the electron energy within wide limits (from a few electronvolts to several hundred electronvolts).     

Diffusion positive column of electric discharge in transverse magnetic field

The effect of a transverse magnetic field on the characteristics of planar diffusion positive column of electric discharge has been studied. It is shown that, as the magnetic induction increases, the distributions of plasma density and particle fluxes to walls become asymmetric; the density maximum shifts in the direction of Ampere’s force action, and the ion flux in this force direction can significantly exceed the reverse flux. It is established that there is a maximum value of magnetic induction, which bounds from above the region of magnetic fields in which a stationary state of the positive column is possible. In the region where a stationary state of the positive column is possible, each value of the magnetic induction corresponds to two positive-column regimes with different values of the electron energy, drift velocity, and electric field strength.     

Characteristics of ions in a magnetized plasma sheath with two species of positive ions

Using the hydrodynamic model, the effects of an external oblique magnetic field and the second ion species density on the characteristics of a three-component (electrons and two species of positive ions) plasma sheath are investigated. It is seen that depending on the magnetic induction of the external field, the velocity and the ion density distributions of both ion species begin to fluctuate. Furthermore, it is shown that density of the second ion species affects the amplitudes of these fluctuations. It is also found that the electrostatic potential of the sheath region depends on the density ratio of positive ion species and by increasing this ratio the electrostatic potential falls down.     

Direct recovery of ion beam energy using magnetic electron suppression: I. Analysis of ORNL energy recovery experiments

The charge-exchange neutralization efficiency of positive ion-based neutral beams used in plasma heating applications decreases as the beam energy increases. Direct energy recovery from the remaining charged particles can be accomplished by electrostatically decelerating the positive ions; the space-charge neutralizing electrons are constrained from being accelerated by the application of a transverse magnetic field. A finite difference nonlinear sheath analysis is used to analyze the transverse magnetic field electron suppression experiments carried out at Oak Ridge National Laboratory in the early 1980s. A double plasma model, which assumes an equilibrium Boltzmann distribution of electrons at both the neutralizer potential and the ion collector potential, is used to study the experimental data obtained from operating 40 keV, 10 A ion beam energy recovery experiments. The effects of the magnetic field strength, ion “boost” energy, and ion beam current density are examined in detail.     

Two-dimensional kinetic model of short high-current vacuum-arc discharge

A two-dimensional mathematical model of a short high-current vacuum-arc discharge is developed, according to which magnetized electrons move in a hydrodynamic regime and fast cathode ions propagate in a free flight regime in a two-dimensional electric field. The proposed model takes into account the distribution of ions with respect to their escape angles from the cathode plasma boundary. A method for calculation of the plasma density distribution in the interelectrode gap is proposed. Two-dimensional distributions of the plasma density, electric field, and discharge current density in an external magnetic field are calculated. It is shown that ion trajectories exhibit mutual intersections, partly return to the cathode, and partly rotate in the oppositely oriented electric field at the side boundary of plasma. A decrease in the applied magnetic field intensity leads to a decrease in the number of ion trajectories reaching the anode (ion starvation), which can result in the violation of a stationary current transfer.     

Calculation of Charge Carrier Concentration Profile in a Wide Potential Well with Electric and Magnetic Fields

We investigated an equilibrium state of Fermi electrons in modulation doped structures with a wide quantum well in a strong parallel magnetic field. We studied the charge carrier system with a sufficiently high density, such that the de Broglie wavelength of electrons is smaller than the potential well width. We have formulated hydrodynamic equations for this carrier system both in the absence of magnetic field and in a parallel magnetic field. We have obtained analytical solutions for the charge carrier concentration as a function of coordinates in the potential well. In a quantum area near the interface, we carried out quantum mechanical calculations taking into account the effect of electric and magnetic fields. The concentration profile is presented for modulation doped Si/SiGe/Si heterostructures. We discuss large positive magnetoresistance in a strong parallel magnetic field in these structures.     

MHD simulation of high-current subsonic vacuum arc under different distributed axial magnetic fields

Based on two-temperature magnetic hydrodynamic (MHD) model, the influence of saddle-shaped distributed axial magnetic field (AMF, linearly increases along radial position) and bell-shaped distributed AMF (linearly decreases along radial position) on plasma loss and heat flux density to anode in subsonic high-current vacuum arc (HCVA) is simulated and analyzed. According to the simulation results, the saddle-shaped AMF can more effectively inhibit plasma loss from arc column than that of bell-shaped AMF. Comparisons between simulation results and experimental results further verify the correctness of model and simulation.     

Numerical simulation of the screw shape of an electric arc in an external axial magnetic field

The characteristics of an electric arc of a direct current, burning in a cylindrical channel in a uniform external axial field, are numerically computed within a nonstationary three-dimensional mathematical model at partial local thermodynamic equilibrium. A method for the numeric modeling of the screw shape of an arc in this field is suggested. This approach is in addition to the “network” analogue of fluctuations for the temperature of electrons, which increases weak numeric asymmetry of electron temperature distribution that occurs randomly during computation. This asymmetry can be “picked up” by an external magnetic field and continue to increase up to a certain value, which is enough to form an arc column screw structure. If there are no fluctuations in the computation algorithm of fluctuations, the arc column in an external axial magnetic field maintains cylindrical axial symmetry and the arc screw shape is not observed.     

Parameters of the positive column of glow discharge with dust particles

We calculate the measured nonlocal parameters of the plasma of the positive column of direct current glow discharge in the presence of dust structures with different dust particle concentrations. The calculations are performed for typical conditions of the positive column of low-pressure glow discharge in air at which a collisional regime of maintaining discharge is achieved. The discharge plasma is described using the diffusion approximation; the flows to the surface of the dust particles are described in the orbital motion limited approximation. Calculation is carried out for micron-size particles with concentrations of up to 10¹¹ m^?3. The distribution of the dust component is assumed to be independent of the discharge parameters. Radial distributions of the plasma components and of the electric field component are obtained. The charges of dust particles for various concentrations and discharge parameters are calculated. It is demonstrated that for a certain particle concentration, the absorption efficiency of plasma particles becomes comparable with diffusion losses at the tube walls. The influence of the dust cloud on the electric field configuration at different dust particle concentrations in the cloud is analyzed. The current-voltage characteristics of the positive column of glow discharge are calculated. A higher discharge stability toward the perturbative action of dust particles at high discharge current values is demonstrated.     

A self-consistent kinetic model of the effect of striation of low-pressure discharges in inert gases

A self-consistent kinetic model is used to treat the effect of striation of the positive column of gas discharge in low-pressure inert gases. The model is based on the solution of the kinetic Boltzmann equation for the electron energy distribution function, of the unsteady-state equation of drift and diffusion for ions, and of the Poisson equation for electric field. Spatial distributions of the electron and ion density are obtained, as well as of the electric field in the positive column of striated discharge. The model is used to explain the kinetic mechanism of origination of the effect of striation in low-pressure inert gases. The obtained distributions are independent of the initial conditions, and the solution gives a self-consistent “resonance” length of strata and the value and form of modulation of electric field.     

Two-fluid MHD model of migma: Equilibrium and stability

MHD equations describing the stable stationary equilibrium of migma plasma are shown to result from the natural evolution of a magnetofluid in which magnetic helicity, cross helicity, and modified kinetic helicity are conserved. These equations are solved in two dimensions to yield distributions of azimuthal velocity, mass density, magnetic field, and current density. The radial expansion of migma as a function of plasma beta (diamagnetism) and the maximum obtainable beta as a function of the uniformity of the vacuum magnetic field are also found. If one assumes that the kinetic pressure is entirely due to Maxwellian electrons, then self-consistent expressions for the electron temperature and radial electric field can be found. The radial ion motions make a non-negligible contribution to the total internal energy, however. Modification to the basic equations arising from finite ion pressure is derived, and some preliminary conclusions are drawn.     

The electron energy distribution in standing striation bands

The electron energy distribution was measured in standing striation bands provoked by a local magnetic field applied to the positive column of a glow discharge plasma in neon. The electron energy distribution function exhibits a pronounced second maximum, the position of which varies depending on the striation region. The experimental results are interpreted in terms of the nonlocal electron kinetics.     

Plasma parameter analysis of Ag sputter deposition using cathodes with different magnetic flux densities

The effects of the magnetic flux density of the Ag sputter target surface on plasma parameters were investigated using the Langmuir probe system in this work. It was found that the electron energy and electron density near the substrate clearly decreased at a high magnetic flux density. In addition, the difference between plasma potential and floating potential (V_p−V_f) decreased at the high magnetic flux density relative to the potentials at the low magnetic flux density. The changes in plasma parameters could be interpreted as the result of many electrons being trapped in the neighborhood of the target surface (cathode sheath) at the high magnetic flux density; hence, the number of electrons in the space near the substrate is reduced. The Ag thin films exhibited low resistivity at a high magnetic flux density. The reduction in resistivity was attributed to the following factors: the low electron energy and electron density near the substrate; the low kinetic energy of positive argon ions; the low kinetic energy of argon atoms backscattered onto the target surface.     

Analysis of H− ion trajectories in a space-charge lens

The success of an electron, space-charge-corrected, solenoidal magnetic lens experiment encouraged the analysis of H⁻ trajectories in a large model-corrected solenoid. With a confined distribution of low energy electrons, the solenoid magnetic flux surfaces define electric equipotential surfaces. The field contribution from trapped electrons cancel net axial electric fields. Negatively charged beam particles then experience a defocusing force which can alleviate spherical aberration. Regions of the magnetic field can be linked by individually biased potential rings to program the correcting electric field. Given a magnetic field distribution, the electric potential distribution required to numerically correct beam particle orbits can be used to determine these ring voltages.     

A two-dimensional mathematical model of a short vacuum arc in external magnetic field: results of numerical calculations

The paper deals with the investigation of the impact made by two-dimensional effects on the process of passage of current in a short vacuum arc in an axial magnetic field. A two-fluid mathematical model is used, which is based on hydrodynamic and electrodynamic equations. The axial magnetic field B _z affects significantly the magnitude of two-dimensional effects: the two-dimensional effects increase with decreasing B _z . The simulation results demonstrate that the contraction of plasma density exceeds that of current density. The distribution of anode drop of potential on the anode surface is nonuniform; in the case of certain (critical) values of current, the anode drop goes to zero on the external boundary of plasma. The dependence of the critical current on B _z is determined. The distribution of current density on the starting plane is nonuniform with a maximum on the axis, and the ion trajectories are inclined to the discharge axis. The possibility is discussed of matching the solution in the plasma region of vacuum arc with that for cathode flames.     

The effects of the operational parameters of the reactor on ECR plasma characteristics

A two-dimensional axis-symmetric model is adopted to investigate the characteristics of an electron cyclotron resonance plasma. The mass conservation equations of electrons, positive ions, and metastable atoms, the electron energy equation, and the Poisson equation are used in this multi-component system. The magnetic field generated by coils was computed numerically. The distributions of temperature and density of electrons are calculated by the finite difference method. The results of the numerical simulation for argon plasma shows that, in the phase of a long-time discharge, the electron temperature in the resonance chamber is higher than that in the reactor chamber, and electron density in the resonance chamber is lower than that in the reactor chamber. In addition, the effects of pressure on the two distributions are illustrated and discussed.     

An investigation of the heating of electrons in multipolar magnet systems and design of low-pressure electron-cyclotron-resonance microwave-frequency reactors

The problem is treated of sustaining plasma in low-pressure electron-cyclotron-resonance plasma reactors in which the main source of ionization is provided by fast electrons blocked in magnetic traps of multipolar magnet systems. The electron-cyclotron heating of electrons by the electric field of a microwave is analyzed. The numerical simulation of the electron motion in magnet systems of various configurations and statistical processing of the calculation results are used to simulate the high-energy part of the electron energy distribution function. It is demonstrated that the main factor defining the electron loss in magnetic traps in the collisionless limit is the departure of fast electrons from magnetic traps to the boundaries of the structure among other things. Comparison is made of different multipolar magnet systems, and the principles of designing optimal electron-cyclotron-resonance MW reactors are formulated.     

Built-in getter-ion pumps

It is shown that theory of the Penning discharge essentially involves taking into account the collective interaction of the electrons in the near-anode region. Following investigations of the Penning discharge in a strong magnetic field (density up to 12 kOe) empirical formulae are proposed for calculating the pumping speed and the minimum operating pressures of getter-ion pumps. Methods of calculation for built-in getter-ion pump parameters and design peculiarities are considered.