Mathematical simulation of the pulsed current amplification mode in a channel of a microchannel plate

The boundary-value problem is solved for electric field in a channel of a microchannel plate under pulsed modulation of the output current. Analytic equations are determined for the field and current in the channel, as well as for the current at the channel exit and for the gain in the time domain. The effect of modulation parameters on the shape of the output current pulses is analyzed.     

Excitation of Nonsymmetric Waves by Given Sources in a Magnetoplasma in the Presence of a Cylindrical Plasma Channel

We consider the problem of excitation of electromagnetic field by spatially bounded, arbitrary given sources in a magnetoplasma in the presence of a cylindrical plasma channel aligned with an external magnetic field. We obtain a rigorous solution for the total field comprising both the discrete and continuous parts of the spatial spectrum of excited waves. Expressions for the radiation pattern and total radiation power of given sources are analyzed. For the whistler range, we calculate the radiation power of a ring electric current located in a channel with enhanced plasma density. It is shown that in this range, the presence of such a channel can lead to a significant increase in the radiation power of ring currents as compared with the case where the considered sources are immersed in a uniform background magnetoplasma, regardless of their orientation.     

Effect of the induced magnetic field on peristaltic flow of a couple stress fluid

We have analyzed the MHD flow of a conducting couple stress fluid in a slit channel with rhythmically contracting walls. In this analysis we are taking into account the induced magnetic field. Analytical expressions for the stream function, the magnetic force function, the axial pressure gradient, the axial induced magnetic field and the distribution of the current density across the channel are obtained using long wavelength approximation. The results for the pressure rise, the frictional force per wave length, the axial induced magnetic field and distribution of the current density across the channel have been computed numerically and the results were studied for various values of the physical parameters of interest, such as the couple stress parameter γ, the Hartmann number M, the magnetic Reynolds number Rm and the time averaged mean flow rate θ. Contour plots for the stream and magnetic force functions are obtained and the trapping phenomena for the flow field is discussed.     

低密度等离子体融断开关的粒子模拟研究

 采用2.5维柱坐标粒子模拟程序研究了低密度等离子体融断开关（PEOS）工作过程中的物理现象,介绍了计算模型的建立和复杂边界的算法处理。模拟结果表明,在PEOS导通电流的过程中,电流通道最初在等离子体的发生器端形成,并且随着导通时间的增大而向负载端漂移。离子的空间分布并没有明显的变化,当PEOS发生断路时,等离子体离子的密度会迅速降低,并最终导致PEOS阴极附近的等离子体的密度已接近为零,此时,阴极电子完全受磁场箍缩作用而不能到达阳极,PEOS完全断开。     

Quantization of acoustoelectric current in a ballistic channel

The electric current induced by an ultrasonic phonon flux in a ballistic quasi-two-dimensional quantum channel is investigated theoretically. Two types of confining potential are considered. An analytic expression for the acoustoelectric current is derived, and its dependence on the chemical potential and on the magnitude of the longitudinal magnetic field is investigated. It is shown that the dependence of the acoustoelectric current on the chemical potential may be of the experimentally observed step type. The oscillatory dependence of the acoustoelectric current on the magnetic field is considered for the cases of weak and strong magnetic quantization.     

雷电回击参数对回击电磁场计算的影响研究

 基于BG，TL，MTLL，MTLE和TCS 5种模型，研究了雷电回击通道高度、回击速度和大地电容率对雷电回击电磁场的影响。计算中5种模型采用相同的通道基电流波形，通过计算总结了几种参数对回击电磁场的影响。     

Towards a programmable magnetic bead microarray in a microfluidic channel

A new hybrid magnetic bead separator that combines an external magnetic field with 175 μm thick current lines buried in the back side of a silicon wafer is presented. A microfluidic channel was etched into the front side of the wafer. The large cross-section of the current lines makes it possible to use larger currents and obtain forces of longer range than from thin current lines at a given power limit. Guiding of magnetic beads in the hybrid magnetic separator and the construction of a programmable microarray of magnetic beads in the microfluidic channel by hydrodynamic focusing is presented.     

Electrical discharge characteristics of a dielectric liquid under external flow in a microchannel with planar electrode configuration

The effect of fluid flow on discharge characteristics in a dielectric liquid was determined. Tests were performed for flow in a 100 micron high, 5 mm wide, 50 mm long microchannel at Reynolds numbers up to 13 and applied DC potentials up to 1.5 kV through 100 micro planar electrode pairs along the floor of the channel. The current within the conduction regime increased as the flow rate increased for the case where the flow was in the same direction as the applied electric field. In the injection regime, there was an optimum flow rate for maximum current.     

Investigation of the redistribution of the current in a nanosecond volume discharge after the appearance of a cathode spot

An investigation was made of the process of contraction of a nanosecond volume discharge in air with a homogeneous field distribution and a current density 500 A/cm² when the gap was 0.7 cm and the pressure 76 torr. It was found that the appearance of a cathode spot in this volume discharge resulted in an effective contraction of the current into a spot and formation of a diffuse channel. A high-conductivity channel emerging from the cathode spot appeared when the current density in the diffusion channel above this spot reached (1–3)·10⁵ A/cm².Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 16–18, January, 1981.     

依据光谱研究闪电回击通道核心的特征参数

闪电回击通道核心中的大电流及其强电磁辐射是引发多种雷电灾害的主要根源。随着现代科技的飞速发展,闪电防护工作显得越为重要。为了完善闪电防护系统,需要从描述闪电回击通道核心的特征参数入手深入研究闪电通道形成和发展过程的微观物理机制。截至目前,光谱观测是获取闪电通道核心特征参数的最佳手段。2015年夏天在青海高原地区的野外试验中,利用由高速摄像机作为记录系统组装的无狭缝光栅摄谱仪,结合快天线地面电场测量仪,记录到一次包括四个回击的云地闪电放电过程的光谱以及与之同步的快电场变化信息。依据光谱,结合等离子体理论计算得到闪电回击通道核心的电导率。在此基础上,应用闪电电动力学模型计算了闪电回击速度、峰值电流、贯穿通道核心的电磁场以及通道核心单位长度的峰值功率等特征参数。结果表明,回击速度在(1.2～2.3)×108 m·s-1的范围内;贯穿回击通道核心的轴向电场、径向电场和磁感应强度的最大值分别在(1.42～1.74)×105 V·m-1,(8.22～9.99)×108 V·m-1和(1.51～2.83) T的范围内。当闪电回击的峰值电流在(7.52～24.05) kA的范围内时,回击通道核心的峰值功率在(0.63～1.92)×109 W·m-1的范围内。另外,分析了电导率、起始电场峰值、回击速度和峰值电流与峰值功率之间的相关性,结果发现峰值电流和峰值功率具有良好的线性关系。研究结果可为探索闪电回击通道形成和发展过程的微观物理机制提供参考依据。     

霍尔推力器磁场位形及其优化的数值研究

基于麦克斯韦方程,在轴对称假设下建立了霍尔推力器磁场的数学模型.用有限差分方法对模型进行了离散.给出了数值求解模型的迭代法.通过对模型的数值求解,得到了相应的数值结果.通过对所得数值结果的分析,研究了磁场线圈电流变化对霍尔推力器磁场位形的影响.通过调整磁场线圈电流的大小找到了理想磁场位形.研究表明,对于理想磁场位形,内通道的磁镜比在3—3.5之间,外通道的磁镜比在0.4—0.9之间;增加磁场线圈的电流,出口的磁场强度随着增加,但不能增加磁镜比.通道内部的磁场强度几乎不随着磁场线圈电流的变化而变化. 关键词： 霍尔推力器 磁场位形 磁场线圈电流 磁镜比     

Liquid Flow in a Porous Channel with Electrokinetic Effects

In this paper, a fully developed laminar flow in a porous channel between two paralleled flat plates in the presence of a double layer electric field is analyzed. The linear Poisson-Boltzmann equation is suggested to model the double layer electric field near the solid-liquid interface. The equation of motion is extended by including the electrical body force generating from the double layer field and then solved analytically. Different from previous models, our proposed one is continuous in the whole flow field and matches commonly-accepted models in the field of fluid mechanics.Besides, the effects of various physical parameters such as the zeta potential, the electrokinetic separation distance, and the ratio of the streaming current to conduction current on the velocity, the pressure, the apparent viscosity of the fluid,as well as the streaming potential are discussed. Physical explanations on the changing trends of those physical quantities with various parameters are given.     

Conductance asymmetry of a slot gate Si‐MOSFET in a strong parallel magnetic field

We report measurements on a Si‐MOSFET sample with a slot in the upper gate, allowing for different electron densities n_1,2 across the slot. The dynamic longitudinal resistance was measured by the standard lock‐in technique, while maintaining a large DC current through the source‐drain channel. We find that the conductance of the sample in a strong parallel magnetic field is asymmetric with respect to the DC current direction. This asymmetry increases with magnetic field. The results are interpreted in terms of electron spin accumulation or depletion near the slot.     

Liquid Flow in a Porous Channel with Electrokinetic Effects

In this paper, a fully developed laminar flow in a porous channel between two paralleled flat plates in the presence of a double layer electric field is analyzed. The linear Poisson-Boltzmann equation is suggested to model the double layer electric field near the solid-liquid interface. The equation of motion is extended by including the electrical body force generating from the double layer field and then solved analytically. Different from previous models, our proposed one is continuous in the whole flow field and matches commonly-accepted models in the field of fluid mechanics. Besides, the effects of various physical parameters such as the zeta potential, the electrokinetic separation distance, and the ratio of the streaming current to conduction current on the velocity, the pressure, the apparent viscosity of the fluid, as well as the streaming potential are discussed. Physical explanations on the changing trends of those physical quantities with various parameters are given.     

Diffusivity and conductivity of a primitive model electrolyte in a nanopore

Equilibrium and non-equilibrium molecular dynamics simulations are applied to obtain the diffusion coefficient and electric conductivity of ions in dilute electrolytes confined in neutral cylindrical pores. The electrolyte is described with the restricted primitive model and the wall of the pore is modelled as a soft wall. The equilibrium molecular dynamics simulations show that the axial diffusion coefficient of ions decreases with increasing confinement. For a fixed pore radius the diffusion coefficient decreases with increasing number density of the ions. The current response of the system to an applied electric field is maintained at constant temperature by Gaussian isokinetic equations of motion, and at constant concentration by periodic boundary conditions with recycling of ions in the axial direction. The electric conductivity is calculated from the current density and the electric field applied for different pore sizes. In contrast to the trend in diffusivity, conductivity increases slightly in smaller pores. For a very small pore, however, conductivity is lower than the bulk, because oppositely charged ions moving in opposite directions under the electric field cannot avoid collisions with each other in a narrow channel.     

Theory of positive corona in SF6 due to a voltageimpulse

A theoretical examination is made of the mechanism of corona formation for a positive point-plane gap in SF₆ at 100 kPa. The impulse voltage applied has a rise time of 15 ns and peak value of 200 kV. Seed electrons are released 1 ns after the start of the voltage rise. For a 0.5-cm diameter positive sphere located 6.5 cm from a negative plane, the calculated circuit current initially consists of subnanosecond corona onset pulses, and then the current steadily rises to a maximum, as the voltage reaches a maximum, followed by a rapid fall in current. During the current rise a streamer moves out into the gap along a 100-μm channel, with the electric field in the streamer trail E>E*, where E* is the critical field where ionization equals attachment. The light output during the discharge is predicted to be a maximum at the anode with only a minor pulse of light at the streamer head, making it hard to detect. After the current maximum, recombination rapidly reduces the numbers of positive ions, negative ions, and electrons, but the net charge density remains constant and thus so does the electric field. The electric field is E~E* in the streamer trail, but has a sharp maximum, E≫E* at the head of the streamer trail. The origin of mid-gap precursors, observed when the streamer channel reilluminates after some 100 ns, is attributed to this field maximum in the remnant electric field. The evolution of positive ions, negative ions, and electrons is described by one-dimensional continuity equations, with the space-charge electric fields determined by the disk method. The effects of ionization, attachment, recombination, electron diffusion, and photoionization are all included. New numerical methods allow resolution of the streamer head and the anode fall region to be obtained with a 1-μm mesh, while following the streamer propagation for ~2 cm     

Magnetohydrodynamic instabilities of a pinch resonant streamer microwave discharge

A pulsed freely localized resonant streamer microwave discharge in air and high-pressure hydrogen in the field of a linearly polarized standing electromagnetic wave in a two-mirror open cavity is investigated. The observed characteristic features of the discharge are treated as consequences of the sausage and wriggle instabilities of the plasma channel with a longitudinal microwave current contracted by its magnetic self-field.     

一种新的磷化铟复合沟道高电子迁移率晶体管小信号物理模型

针对磷化铟(InP)复合沟道高电子迁移率晶体管(HEMT)的特点，对常规单沟道HEMT的小信号物理模型进行了修正，提出了一种新的用于复合沟道HEMT的小信号物理模型，用商用器件模拟软件ISE(integrated systems engineering)对其进行了仿真验证，对比了实测和仿真的I-V特性及转移特性曲线，重点研究了在InGaAs/InP双层沟道中考虑量子效应后的电场和电流密度随着不同栅电压的变化趋势，研究结果表明，由于在沟道中存在量子效应，在栅下靠源端低电场区域，电流主要分布在InGaAs沟道 关键词： 高电子迁移率晶体管 复合沟道 物理模型 磷化铟     

Excitation of the Potential Relaxation Instability in a Weakly Magnetized Discharge Plasma by a Voltage Step

An instability is triggered in a weakly magnetized discharge plasma by the application of a positive voltage step to a planar collector immersed into the plasma column with its surface perpendicular to the magnetic field lines. Time developement of the plasma density after the application of the pulse is measured by a Langmuir probe. Radial and axial velocity of the plasma density perturbation are measured. Radial velocity is consistent with the increase of the plasma potential in the current channel. Axial velocity is very high. It is interpreted as phase velocity of radial quasiperiodic motion of the plasma in and out of the current channel. Response time of the collector current to the applied voltage step is measured versus different parameters. Experimental results are in agreement with a qualitative model presented in previous work [1] where the observed instability is modeled as a two dimensional potential relaxation instability (PRI). Minor improvements of the previous model are proposed. A rarefaction pulse that moves towards the collector is found as the initial stage of the instability.     

Investigation of a Hall MHD channel with an ionization-unstable plasma of inert gases

We investigate a promising scheme for using ionization-unstable plasmas of pure inert gases as the working medium for a magnetohydrodynamic (MHD) closed-cycle generator. Our experiments were carried out using a disc Hall MHD channel, with the flux of ionized gas created in a shock tube. Our working gas was xenon. In these experiments we measured the gas pressure, the flow velocity, the concentration and temperature of the electrons, the azimuthal current density, the distribution of potential in the channel, and the value of the near-electrode voltage drop. We recorded voltage-current characteristics for various values of magnetic field and load resistances. The results of these experiment showed that in an ionization-unstable plasma of inert gases without admixtures of alkali metal, the effective conductivity in the Hall channel increases significantly with increasing degree of criticality of the magnetic field, and the value of the maximum specific power extracted increases more rapidly than the specific power calculated by assuming “frozen” ionization. Zh. Tekh. Fiz. 67, 6–11 (December 1997)