Two-dimensional model of the Penning discharge in a cylindrical chamber with the axial magnetic field

The drift–diffusion model of a Penning discharge in molecular hydrogen under pressures of about 1 Torr with regard to the external electric circuit has been proposed. A two-dimensional axially symmetric discharge geometry with a cylindrical anode and flat cathodes perpendicular to the symmetry axis has been investigated. An external magnetic field of about 0.1 T is applied in the axial direction. Using the developed drift–diffusion model, the electrodynamic structure of a Penning discharge in the pressure range of 0.5–5 Torr at a current source voltage of 200–500 V is numerically simulated. The evolution of the discharge electrodynamic structure upon pressure variations in zero magnetic field (the classical glow discharge mode) and in the axial magnetic field (Penning discharge) has been studied using numerical experiments. The theoretical predictions of the existence of an averaged electron and ion motion in a Penning discharge both in the axial and radial directions and in the azimuthal direction have been confirmed by the calculations.     

DC column plasma kinetics in a longitudinal magnetic field

The cylindrical column plasma of a neon dc glow discharge under the influence of a weak longitudinal magnetic field is studied. An extended, fully self-consistent model of the column plasma has been used to determine the kinetic quantities of electrons, ions and excited atoms, the radial space charge field, and the axial electric field for given discharge conditions. The model includes a nonlocal kinetic treatment of the electrons by solving their spatially inhomogeneous kinetic equation, taking into account the radial space charge field and the axial magnetic field. The treatment is based on the two-term expansion of the velocity distribution and comprises the determination of its isotropic and anisotropic components in the axial, radial, and azimuthal direction. A transition from a distinctly nonlocal kinetic behavior of the electrons in the magnetic-field-free case to an almost local kinetic behavior has been found by increasing the magnetic field. The establishment of the electron cyclotron motion around the column axis increasingly restricts the radial electron energy transport and reduces the radial ambipolar current. The complex interaction of these transport phenomena with the alterations in the charge carrier production leads finally to a specific variation of the electric field components. The axial field increases by applying weak magnetic fields, however, decreases with increasingly higher magnetic fields. At higher magnetic fields, the radial space-charge field is considerably reduced     

Determination of the wave number of an electromagnetic wave propagating in high-frequency jet discharge plasma

The measurements of the amplitude-phase characteristics of the electromagnetic field in a high-frequency jet discharge burning in air and argon have been performed. Experimentally obtained radial distributions of the radial component of the electric field gave the base to determine the value of the wave number of an electromagnetic wave which propagates in the HF jet discharge plasma. The axial distribution of the radial component of the electric field has been calculated from the model of a jet discharge channel formed as a finite-length electric line.     

Distribution of electric field in the round hole of plane capacitor

A planar capacitor with a round hole, filled by electrorheological fluid, can be used to design valves controlled by an electric field. To design valves effectively, the distribution of the electric field within the hole must be known. When the distribution along the axis of the hole is known, the electric field can be calculated at any point inside the hole. Relative coordinates, such as the ratio of values of real coordinates to the half height of the capacitor, and relative parameters, such as the ratio of the values of the outside electric field to the field inside the capacitor, are utilized in this study. The electric field on the axis of the hole is found in two steps. First, the electric field along the axis of symmetry between two plane capacitors is calculated by finding the field distribution near the edge of the detached plane of a two-plane capacitor, then the redistribution of the charges on the plate of the capacitor, due to influence of the neighbouring capacitor plate is evaluated. Second, the electric field along the axis of the round hole is calculated, thus allowing us to evaluate an alternative mechanism for charge redistribution from the plane parallel case to the case of a field with axial symmetry. Results show that the field in the hole becomes weaker when the hole is filled with a liquid of relative permittivity higher than unity. Diminution of the field can be avoided by filling the area on the capacitor with the medium of the same or greater permittivity.     

Inreased Power Concentration and its Effect on the Discharge Parameters on the Low Pressure Hg-Rare Gas Positive Column III. Effects of an Axial Rod

After the investigation of the influence of current and tube radius on the power concentration of the Hg-rare gas discharge in the two previous parts, part III deals with the corresponding effects of additional recombination surfaces. The plasma parameters (radiant flux of the resonance lines, field strength, electron density, electron energy distribution function) are measured in a discharge tube with an axial glass rod. With increasing rod diameter and increasing distance from the tube axis radial radiation intensity distribution becomes asymmetric. The field strength increases with the radius of the rod. The dependence of the field strength and that of the radiant flux on the parameters of the discharge do not basically change. The measured UV-radiation efficiency of the positive column is higher than that of discharges without axial rod for equal tube radius. This is attributed primarily to the changed radial electron density distribution and its effect on the collision processes.     

形状与位置对断点划痕场分布的影响研究

用3维时域有限差分方法分别研究了在355 nm入射激光作用下, 熔石英后表面具有不同形状 和位置的断点划痕对场分布的影响.研究表明,对于椭圆状的坑点, 当共线的轴长逐渐 增大时, 电场幅值与强点数目先增大后减小, 获得最大光强增强因子的两轴 比是1.1-1.2, 此时坑点呈近圆形. 当平行的轴长逐步增大时,电场幅值先逐渐增大, 当两轴比为0.53时趋于平缓, 而强点总数则呈"J"形曲线不断增长. 当坑点尺寸相同 但排放位置不同时, 相邻坑点的相对面积愈大, 调制愈强.     

Spatial electric field effect in GaAs–AlAs quantum wires

The response of an electron to a three-dimensional electric field in an infinite quantum well wire of square cross-section is investigated within a variational scheme. The ionization energy and the polarization are calculated for different locations of impurity ion. It is found that the results for the spatial electric field differ from the previous results found for the electric field applied in the direction perpendicular to the wire axis. The ionization energy weakens rapidly with the axial component of the field as the polarization of the carrier distribution intensifies.     

Measurement of intense microwave field patterns using a neon glow indicator lamp

A novel method using small neon glow lamps with electrodes is developed for measuring intense microwave field patterns. When the lamp axis coincide with the electric field direction, the lamp discharge starts at the feeblest microwave electric field strength. Therefore, the lamp axis shows the field direction and the discharge starting indicates the field strength. The field strength for starting the microwave discharge is less than the strength for AC discharge, because of its low loss discharge mechanism. In the experiments using a microwave oven, it has been demonstrated again comparing with the simulated results that the method is able to use for measuring the intense electric field strength and direction.     

Experimental investigation of the gas discharge dynamics in a solenoidal magnetic field

An electric gas discharge is initiated at the end face of a nonconducting cylinder between a central electrode coaxial with the cylinder and a ring electrode on the lateral surface of the cylinder. The axis of the cylinder and that of a magnetic coil wound on its lateral surface coincide. The dynamics of the gas discharge in a solenoidal magnetic field is studied by observing its position and shape and monitoring the variation of the thermionic center distribution on the surface of the ring electrode with discharge current and magnetic induction. The discharge develops in air at a pressure of 2 kPa.     

The influence of a transverse magnetic field on a subnormal glow discharge in air

In subnormal glow discharge under d.c. excitation at different pressure in a varying transverse magnetic field (0 to 30 G) some measurements have been carried out for various initial average tube currents. The voltage across the discharge increases and average tube current and residual current decreases in the magnetic field. With the help of Beckman’s expression [4] for the axial field and the electron density distribution in a transverse magnetic field the observed variation of current and voltage can be satisfactorily explained. The variation of axial electric field with transverse magnetic field can be represented to a fair degree of accuracy by the derived equation. The behaviour of residual current with magnetic field has been observed in these oscillations.     

Modelling of the Positive Column in an Argon-Hexamethyl-disiloxane dc Glow Discharge

A model is presented of the positive column of a dc glow discharge in argon with small admixtures of hexamethyldisiloxane (HMDS). The axial electric field, the ion production rates for direct-, stepwise-, pair-, and Penning ionization, the densities of metastable Ar atoms and of electrons, and the wall current of HMDS ions are calculated in dependence on HMDS admixture and discharge current density. For the calculations particle balance equations were used for a diffusion determined plasma in a mixture of two gaseous components. The reaction rates for the electron collision processes were determined applying the electron distribution function calculated for pure argon. Taking into account PENNING ionization of HMDS molecules by metastable argon atoms the decrease of electric field for increasing HMDS admixtures is according to the experimen-tally measured values. Also ion wall currents and electron densities are compared with experimen-tal values for thin film formation rate and results of probe measurements.     

双频容性耦合CF4等离子体放电的二维混合模拟

研究了等离子体反应装置内的等离子体密度、粒子能量与角度分布等参量在装置径向与轴向上的分布特性。在研究过程中应用二维混合模型对CF4气体放电进行模拟。计算结果显示：在电极表面与侧壁附近的鞘层区特性有明显的区别。由于装置侧壁处受电源产生的射频电场的影响较小,侧壁处的鞘层主要由双极扩散机制形成,其产生的径向电场强度较弱,鞘层厚度也较薄。而在电极附近,由于受到射频电场的影响,鞘层的厚度显著增加,指向电极方向的轴向电场强度也远大于指向侧壁方向的径向电场强度。在电极区域内,离子通量分布均匀;在电极边缘与侧壁的间隙内,因电场强度减小,离子通量则发生迅速衰减。在射频电极覆盖的范围内离子能量分布大体上保持不变,电极与侧壁的交界处,由于受到侧壁处径向电场的影响,离子能量分布略有不同。在放电装置的中心区域,入射到电极上的离子角度分布基本保持一致,而在电极边界与装置侧壁的交界处,由于径向电场的影响,离子的垂直入射角增加,以大角度轰击电极的离子数量也显著增加。     

双频容性耦合CF4等离子体放电的二维混合模拟

研究了等离子体反应装置内的等离子体密度、粒子能量与角度分布等参量在装置径向与轴向上的分布特性。在研究过程中应用二维混合模型对CF4气体放电进行模拟。计算结果显示:在电极表面与侧壁附近的鞘层区特性有明显的区别。由于装置侧壁处受电源产生的射频电场的影响较小,侧壁处的鞘层主要由双极扩散机制形成,其产生的径向电场强度较弱,鞘层厚度也较薄。而在电极附近,由于受到射频电场的影响,鞘层的厚度显著增加,指向电极方向的轴向电场强度也远大于指向侧壁方向的径向电场强度。在电极区域内,离子通量分布均匀;在电极边缘与侧壁的间隙内,因电场强度减小,离子通量则发生迅速衰减。在射频电极覆盖的范围内离子能量分布大体上保持不变,电极与侧壁的交界处,由于受到侧壁处径向电场的影响,离子能量分布略有不同。在放电装置的中心区域,入射到电极上的离子角度分布基本保持一致,而在电极边界与装置侧壁的交界处,由于径向电场的影响,离子的垂直入射角增加,以大角度轰击电极的离子数量也显著增加。     

An Investigation of Coupled D. C.-Induction Arc Discharges

The object of this study is to analytically determine the properties of an arc discharge generated by a combination of induction and d. c. electromagnetic fields. Induction power is supplied to the discharge by a solenoidal coil whose axis of symmetry is aligned with the applied d. c. electric field. A numerical technique is used to simultaneously solve a set of linear differential equations which include Maxwell's field equations, the single fluid energy equation, the momentum balance equation, Ohm's law, and the radiation diffusion equation. It is necessary to make a number of reasonable assumptions to obtain the final set of equations for programming. These assumptions restrict the calculations to azimuthally symmetric plasmas with axial gradients only in static pressure. In addition, the radiant energy flux is assumed to be isotropic within the plasma.     

Amplitude—frequency characteristics of an electromagnetic field in the high-frequency torch discharge

Measured axial distributions of harmonic components of the electric field of the torch discharge in argon at different frequencies of the fundamental harmonic are presented. It is found that the fourth electromagnetic field harmonic decays in the resonance manner.     

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.     

Standing Waves along a Microwave Generated Surface Wave Plasma

Two surface wave plasma columns, generated by microwave power in argon at gas pressures of 0.05 torr to 330 torr, interact in the same discharge tube to form standing surface waves. Radial electric field Er and azimuthal magnetic field H? outside the discharge tube are measured to be 90° out of phase with respect to axial position and to decay exponentially with radial distance from the tube axis. Maximum light emission occurs at the position of maximum H?, and minimum Er. Electron temperature and density are measured at low pressures with double probes inserted into the plasma at a null of Er. Measured electron densities compare well with those predicted by Gould-Trivelpiece (GT) surface wave theory. Measured electron temperatures are the same order of magnitude as temperatures predicted by positive column theory.     

微空心阴极放电时空特性

为了揭示微空心阴极放电的放电机理,利用流体模型研究了矩形微空心阴极放电的时间和空间分布特性。在氩气环境下计算得到了压强为1.3104Pa时电流、电势、电场、电子和离子密度等随时间的发展变化。结果表明,整个放电过程分为四个阶段,即预放电阶段、电场由轴向向径向转换阶段、电流缓慢增长向空心阴极效应过渡阶段和稳态放电阶段。稳态放电时出现明显的空心阴极效应,阴极位降区存在很高的径向电场和较高的电子平均能量,而负辉区径向电场很弱,电子平均能量较低,电子和离子密度峰值出现在负辉区,二者数值基本相等,而在阴极位降区离子密度远高于电子密度。     

微空心阴极放电时空特性

为了揭示微空心阴极放电的放电机理,利用流体模型研究了矩形微空心阴极放电的时间和空间分布特性。在氩气环境下计算得到了压强为1.3×10~4Pa时电流、电势、电场、电子和离子密度等随时间的发展变化。结果表明,整个放电过程分为四个阶段,即预放电阶段、电场由轴向向径向转换阶段、电流缓慢增长向空心阴极效应过渡阶段和稳态放电阶段。稳态放电时出现明显的空心阴极效应,阴极位降区存在很高的径向电场和较高的电子平均能量,而负辉区径向电场很弱,电子平均能量较低,电子和离子密度峰值出现在负辉区,二者数值基本相等,而在阴极位降区离子密度远高于电子密度。     

The Influence of a Longitudinal Magnetic Fields on a Non‐Uniform Positive Column

The variations of plasma parameters of a dc discharge in a non‐uniform magnetized plasma were measured using fast floating double Langmuir probes. A solenoid is used to produce a uniform magnetic field parallel to the discharge axis. The axial changes of the plasma parameters are presented in the range of longitudinal magnetic fields 200 to 600 Gauss at the pressure range 0.3 to 2.1 Torr and discharge currents 5 and 15 mA in argon gas. The experimental results indicate that, as a consequence of the axial magnetic.eld and the variations in the discharge tube radii, the plasma parameters at small radius exhibit obvious changes in their distributions along the axis compared to the situation of unmagnetized plasma. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)