Self-consistent structure of a dc discharge with a closed hall current in crossed electric and magnetic fields

A dc glow discharge with a closed Hall current in crossed electric and magnetic fields in helium is investigated. It is shown that the main features of an unmagnetized dc discharge [1] (such as the separation of the discharge into a space charge sheath and a quasineutral plasma, the formation of a cathode fall region and a negative glow, the appearance of a region with a reversed electric field producing a potential well for low-energy electrons and resulting in the formation of a Faraday dark space, and the formation of three pronounced groups of electrons in the electron distribution function) are also retained in a discharge in crossed fields. It is found that the sheath length is almost independent of the magnetic field, while the length of the negative glow region decreases appreciably with increasing magnetic field. The measured electron distribution function agrees well with the nonlocal theory, according to which the current in the Faraday dark space is carried by the intermediate electrons that are not trapped in the potential well and the energies of which are lower than the first excitation energy.     

Confinement physics for thermal, neutral, high-charge-state plasmas in nested-well solenoidal traps

A theoretical study is presented which indicates that it is possible to confine a neutral plasma using static electric and solenoidal magnetic fields. The plasma consists of equal temperature electrons and highly stripped ions. The solenoidal magnetic field provides radial confinement, while the electric field, which produces an axial nested-well potential profile, provides axial confinement. A self-consistent, multidimensional numerical solution for the electric potential is obtained, and a fully kinetic theoretical treatment on axial transport is used to determine an axial confinement time scale. The effect on confinement of the presence of a radial electric field is explored with the use of ion trajectory calculations. A thermal, neutral, high-charge-state plasma confined in a nested-well trap opens new possibilities for fundamental studies on plasma recombination and cross-field transport processes under highly controlled conditions.     

对超热电子诱生的磁场分布的估算

利用简化模型估算了电荷分离场及由超热电子逃逸在等离子体表面产生的自生磁场的大小和空间分布.受电荷分离场的影响以及超热电子逃逸数的限制,超热电子产生的环形磁场主要分布于等离子体表面附近的焦斑半径内,仅当超热电子束流很强时(在1μm半径截面内达到kA量级),环形磁场才可以达到10²T量级.一般情况下,由超热电子产生的磁场则极小 关键词： 磁场 超热电子     

Z箍缩等离子体磁重联现象

分析了磁重联对晕等离子体加速和能量平衡过程的影响。分析表明晕等离子体向轴心的加速过程分为两个阶段:第一阶段晕等离子体在磁压或热压(依赖于丝数)作用下向轴心运动;第二阶段晕等离子体由于磁重联过程被加速到阿尔芬速度,并到达轴心形成先驱等离子体。估算表明重联层的厚度与离子的惯性长度具有相同的数量级,电流片内电子运动和离子的运动是解耦合的。在内爆滞止阶段电荷分离产生强的径向电场,这个电场将磁能转化为等离子体轴向(z方向)动能,内爆动能和轴向动能共同转化为X射线辐射能,以此解释了X射线能量大于内爆动能这一观测结果。分析了磁重联电磁脉冲的性质,对于1 MA驱动条件,电磁脉冲的总能量可达kJ量级。     

Z箍缩等离子体磁重联现象

分析了磁重联对晕等离子体加速和能量平衡过程的影响。分析表明晕等离子体向轴心的加速过程分为两个阶段:第一阶段晕等离子体在磁压或热压(依赖于丝数)作用下向轴心运动;第二阶段晕等离子体由于磁重联过程被加速到阿尔芬速度,并到达轴心形成先驱等离子体。估算表明重联层的厚度与离子的惯性长度具有相同的数量级,电流片内电子运动和离子的运动是解耦合的。在内爆滞止阶段电荷分离产生强的径向电场,这个电场将磁能转化为等离子体轴向(z方向)动能,内爆动能和轴向动能共同转化为X射线辐射能,以此解释了X射线能量大于内爆动能这一观测结果。分析了磁重联电磁脉冲的性质,对于1 MA驱动条件,电磁脉冲的总能量可达kJ量级。     

Wall Recombination in Glow Discharges

We derived a model describing the radial distribution of the ion and electron densities and the radial electric field strength in the positive column of a glow discharge. The set of equations related to the plasma consists of the equations for particle and momentum conservation for the ions and electrons and the Poisson-equation. In a novel approach, the necessary boundary conditions in our model result from a system of balance equations for the charge carriers on the insulated wall surrounding the positive column.     

对超热电子诱生的磁场分布的估算

利用简化模型估算了电荷分离场及由超热电子逃逸在等离子体表面产生的自生磁场的大小和空间分布.受电荷分离场的影响以及超热电子逃逸数的限制,超热电子产生的环形磁场主要分布于等离子体表面附近的焦斑半径内,仅当超热电子束流很强时(在1μm半径截面内达到10³A量级),环形磁场才可以达到10²T量级.一般情况下,由超热电子产生的磁场极小. 关键词： 磁场 超热电子     

Mechanism of diffusion of positively charged dust particles in a photoemission cell under microgravity conditions

The decay of a dusty plasma in a photoemission cell under microgravity conditions is investigated on the basis of the method of nonlocal moments. It is founds that plasma decay in space experiments occurs in accordance with the mechanism of free electron diffusion followed by dust particle drift. An analytic solution is found for the evolution of radial distributions of the dust particle concentration and the electric field under the experimental conditions. The effect of abnormally high temperatures of dust particles is considered. The effect of axial magnetic fields on the decay of dusty plasma is investigated. It is shown that the plasma decay in a magnetic field is governed by the ambipolar diffusion mechanism, the decay being prolonged up to 10³ s in a magnetic field on the order of 10³–10⁴ G in strength.     

Magnetic Vortex Tubes in Astrophysics

The viscous forces on electrons and ions in a differentially rotating plasma drive an azimuthal current density j?, with axial magnetic field Bz which is shown to be proportional to plasma vorticity. Field strengths in agreement with those observed for both stars and galaxies are obtained, assuming that reactive forces prevent radial drifts of electrons or ions. Hierarchical vorticity is required in order to reconcile the small-scale length required for field changes with the large-scale length of observed fields. A vortex tube with magnetic field (magnetic vortex tube-MVT) becomes the basic entity for the origin of magnetic fields. Twisting of field lines by differential rotation causes (1?,Bz,) ?(jz, B?,). When jzB?, > j?, Bz the MVT suffers magnetic pinch, and the axial current in the pinch flows through a cylindrical sheath with a radial electric field due to plasma polarization. An instability of drift velocity denudes a length R of the current channel of free charges, and the inductively maintained current then requires a displacement current in R and hence a growing axial electric field Ez, Ez is limited by transfer of the energy in B?, to Ez, and thereafter the energy oscillates between the fields. On the stellar scale, evidence for polar MVT's comes from young stars with bipolar outflows of gas and jets. It is argued that end-on viewing of polar MVT's accounts for the kilogauss fields of Ap stars and the 1-100-MG fields of magnetic white dwarfs.     

Gas-filled electron diode based on a glow discharge

Stable ignition and sustention of a pulsed discharge with a current of up to 180 A and duration of 12 μs at a pressure of 10⁻¹–10⁻² Pa are achieved in a glow-discharge plasma cathode with the help of an auxiliary initiating discharge. An electron emission current density of up to 100 A/cm² and accelerating voltageof 15 kV are obtained in a gas-filled diode based on this type of a plasma cathode. An electron beam witha neutralized space charge can be transported almost without losses in a weak axial magnetic field alonga plasma channel formed due to the gas ionization by the accelerated electrons over a distance of up to 30 cm.     

Vacuum Arc Plasma Centrfuge for Element and Isotope Separation

Vacuum arcs have been studied extensively in the past several decades with applications primarily in the areas of switching, vacuum remelting, and vapor deposition. Application of the vacuum arc for element and isotope separation has been studied recently and is reviewed in this paper. An arc was produced in a 30-cm-diameter 4-m-long cylindrical chamber with coaxially mounted electromagnets providing a 2.6-m-long constant axial magnetic field of up to 6 kG. The vacuum discharge between a solid cathode and a mesh anode was triggered electrically. A pulse-forming network (PFN) of 70-m? impedance provided nearly constant-current discharge pulses of several kiloamps and 6-12-ms duration. The magnetized plasma column, flowing axially from the anode with a typical velocity of 106 cm/s, rotated nearly as a solid body. This rotation was due to the E × B drift, produced by the axial magnetic field and the radial electric field across the column. A typical rotation frequency was 105 rad/s. The centrifugal effect due to the rotation caused a radial redistribution of ions within the plasma column, thereby producing elemental and isotope enrichment. The separation was observed to increase exponentially with the square of the radius. Enrichments of up to 300 percent were measured in a Cu-Zn plasma. The radial plasma density profile was found to be roughly Gaussian, with central electron densities of about 1013 cm-3. The radial potential profile across the column was measured and found to be parabolic with radius.     

Trapped-particle-mediated collisional damping of nonaxisymmetric plasma waves

Weak axial variations in magnetic or electric confinement fields in pure electron plasmas cause slow electrons to be trapped locally, and collisional diffusion across the trapping separatrix then causes surprisingly large trapped-particle-mediated (TPM) damping and transport effects. Here we characterize TPM damping of m theta not equal to 0, m(z) = +/-1 Trivelpiece-Gould plasma modes in large-amplitude long-lived Bernstein-Greene-Kruskal states. The TPM damping gives gammaBGK/omega approximately 10(-4) and seems to dominate in regimes of weak interparticle collisions.     

Heating mechanism in one-dimensional bounded magnetized inductively coupled plasma

A self-consistent nonlocal kinetic model has been established to investigate the electron heating mechanism in an one-dimensional bounded magnetized inductively coupled plasma (MICP) under low pressures. The interaction function of electrons with rf electric field and electron energy distribution function (EEDF) are determined by solving the linearized Boltzmann equation incorporating with the Maxwell equations. The numerical results show that the presence of the direct-current (dc) magnetic field plays an important role in the EEDF and high-energy electrons are efficiently heated by the Azbel–Kaner resonances under the anomalous skin-effect conditions.     

Self-consistent hybrid model for a stratified positive column of a low pressure glow discharge

The stratification of a positive column of a low-pressure glow discharge in inert gases has been studied with the help of a self-consistent hybrid model. The model is based on the solution of a nonlocal kinetic Boltzmann equation for the electron distribution function, a nonstationary drift-diffusion equation for the ions, and the Poisson equation for the electric field. Spatial electron and ion density distributions and the electric field distribution in the positive column were obtained. The converged solution of the model gives a self-consistent resonant strata length L and the value and the form of the modulated plasma parameters. An unexpected surprising result was obtained: for a given potential drop in the positive column of a low-pressure glow discharge, a self-consistent spatially modulated striation-like electric field does not lead to the resonant increasing of the ionization frequencies in the discharge as compared with a constant electric field with the same potential drop. Usually, it was assumed that, in spatially modulated field distributions, all the parameters in a striated plasma will be more pronounced and have a resonant form. The text was submitted by the authors in English.     

Particle-in-cell simulation for different magnetic mirror effects on the plasma distribution in a cusped field thruster

Magnetic mirror used as an efficient tool to confine plasma has been widely adopted in many different areas especially in recent cusped field thrusters. In order to check the influence of magnetic mirror effect on the plasma distribution in a cusped field thruster, three different radii of the discharge channel(6 mm, 4 mm, and 2 mm) in a cusped field thruster are investigated by using Particle-in-Cell Plus Monte Carlo(PIC-MCC) simulated method, under the condition of a fixed axial length of the discharge channel and the same operating parameters. It is found that magnetic cusps inside the small radius discharge channel cannot confine electrons very well. Thus, the electric field is hard to establish. With the reduction of the discharge channel's diameter, more electrons will escape from cusps to the centerline area near the anode due to a lower magnetic mirror ratio. Meanwhile, the leak width of the cusped magnetic field will increase at the cusp. By increasing the magnetic field strength in a small radius model of a cusped field thruster, the negative effect caused by the weak magnetic mirror effect can be partially compensated. Therefore, according to engineering design, the increase of magnetic field strength can contribute to obtaining a good performance, when the radial distance between the magnets and the inner surface of the discharge channel is relatively big.     

A steadily rotating plasma disk

A homogeneously rotating plasma disk can be formed in a radially directed Ar-arc discharge at reduced pressure with an externally applied axial magnetic field. The radial pressure distribution is measured, as well as the emitted continuum radiation and the arc voltage. With these experimental values profiles of temperature, radial and azimuthal current density, and flow velocity in the disk are evaluated. Viscosity determines the flow pattern essentially. The effects of magnetic field and rotational motion on the discharge are investigated. The disk exhibits at nonrigid rotation a strong centrifugal force and a minor Coriolis force. A weak double vortex is found to develop in the meridional plane. The electric field in the discharge is altered by the azimuthal plasma flow.     

Radial distribution of plasma density in the positive column of thehigh-current stationary glow discharge

A model is presented which describes the radial distributions of the plasma density, electric potential, current density, and magnetic field in the positive column of a stationary glow discharge not in contact with the longitudinal walls of the discharge chamber. In this model, the compression of the positive column is provided by the azimuthal magnetic field created by the discharge current. The value of, the discharge current is obtained for the case where charged-particle diffusion is balanced by the actions of the radial electric field and the magnetic pinch effect. The radial distributions of plasma parameters are also calculated for the case of high-current glow discharges where charged-particle diffusion can be ignored