A model for the operation of a laser-triggered vacuumlow-inductance switch

A new model for the operation of a laser-triggered vacuum switch utilizing a composite target pellet in the cathode is given along with supporting experimental results. It is shown that two separate mechanisms are responsible for the operation of the switch, namely, a thermal mechanism for the initial current flow and an ion regeneration mechanism for the current buildup. The current buildup is strongly dependent upon geometry, as is evident from the experiments with 3- and 1-mm apertures in the anode. The jitter time is primarily determined during current buildup and nearly independent of the laser energy. An ion regeneration mechanism is consistent with the experimental data for current buildup, and a thermal mechanism is consistent with the initial generation of current     

Measurement of high-order current correlators

The feasibility of measuring high-order current correlators by means of a linear detector is analyzed. Two different types of measurements are considered: measurement of fluctuation power spectrum and measurement of unequal-time current correlators at fixed points in time. In both cases, formally exact expressions in terms of Keldysh time-ordered electron current operators are derived for the detector output. An explicit time ordering is found for the current correlators under the expectation operator used in measurements of high-order unequal-time current correlators. The situation when a detector measures current correlators at different points of a conductor is considered.     

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.     

Mathematical model of the direct 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 for a preset value of current at the channel entrance. Analytic equations are determined for the distributions of field, potential, and current along the channel, as well as for the current gain and the current in the circuit of the source of constant voltage as a function of the input current.     

Total Current Operator and its Classical Correspondence for Particles Bounded in Central Force Fields

When a particle is bounded in a central force field, the only nonvanishing component of the mean value for current density is along the azimuthal direction; and the total current can therefore be defined. It is found that the total current is in fact a mean value of a newly defined total current operator in the quantum mechanical state. Not only the total current operator itself but also the mean total current has exact classical correspondence.     

Nonlinear magnetic field diffusion in a substance metallized by shock compression

The problem of nonlinear magnetic field diffusion in a substance metallized by shock compression is considered. The problem is solved numerically for various time dependences of the current through the conducting region (direct current, linearly increasing current, and the current increasing as the square root of the time). Nonlinear diffusion leads to qualitative changes in the structure of the current in the substance being metallized. In this case, the maximal current density is shifted from the conducting boundary (at which it is located in the case of linear diffusion) to the bulk of the conducting material. For strong nonlinear diffusion and an increasing boundary magnetic field, the current density peak may approach the shock front. The numerical solution obtained here is compared with the analytic solution obtained earlier for linear diffusion.     

Electronic phenomena in semi-conductors with a temperature gradient

Phenomena connected with the transfer of current carrier concentrations as a result of a temperature gradient in semi-conductors with two kinds of current carriers are theoretically studied. The paper first deals with the general equations which are valid at a certain point of the semi-conductor with a temperature gradient for the concentrations of current carriers and density of electric and thermal current. From this the distribution of the concentrations of current carriers is found for a typical case, the phenomenon of thermal emission of minority current carriers is discussed, relations are derived for the dependence of the thermal emf on the magnitude of the temperature gradient, the possibility is discussed of thermal rectification and equations are given for the thermal conductivity of a semi-conductor with non-equilibrium concentrations of current carriers.     

色散效应对聚光多结太阳电池性能的影响及优化

针对色散效应导致聚光多结太阳电池性能降低的问题,使用分布式三维等效电路模型计算高倍聚光下GaInP/GaInAs/Ge三结太阳电池的输出特性,通过分析电池各层的电压分布、暗电流分布以及横向电流分布,研究了不同电池尺寸下色散效应对电池性能影响的机理.结果表明:色散使多结太阳电池在局部区域的光生电流变得不匹配,随着电池尺寸的减小,局部区域之间失配的光生电流能够以横向电流的形式相互补偿,使电池整体的电流更加匹配,从而减小色散效应的影响.当电池芯片尺寸较大(20 mm×20 mm)时,色散主要降低电池的短路电流密度,色散光斑下电池的效率仅相当于无色散时的94%;当电池芯片尺寸减小到2 mm×2 mm时,短路电流密度与无色散时相等,但横向电阻降低了电池的填充因子.当电池芯片尺寸进一步减小到0.4 mm×0.4 mm时,色散与无色散光斑下电池的各项性能几乎没有差别,效率均约为34.5%,色散效应的影响可忽略不计.     

SC-200质子加速器输运部磁体电源的输出纹波形成机理分析及其Simplorer仿真

介绍了质子治疗加速器输运部二极磁铁电流源的技术要求、主电路拓扑。该电源要求输出电流精度为25ppm，纹波小于25ppm。电源输出电流纹波由低频纹波和高频纹波组成。对电源输出电流纹波的形成机理进行了详细的理论分析和数学计算。得出了基于冲量控制原理的脉冲宽度调制(PWM)电流跟踪控制技术可以有效消除输入低频纹波对输出电流的影响。同时也对输出电流高频纹波采用两种方法进行了定量的数学分析，并得出量化的结论和计算公式。借助AnsoftSimplorer电路仿真软件构建模型，验证了纹波规律结论及计算公式的准确性，并且提出了相应的纹波抑制策略。     

一种用于弧流电源的新型打坑电路设计

作为中性束注入加热系统的核心设备,弧流电源的性能至关重要。打坑电路是弧流电源的重要组成部分,其动态响应特性及稳定性决定了弧流电源的性能。提出了一种用于弧流电源的新型打坑电路解决方案,能在150 μs内快速实现大电流的跌落和恢复,并且跌落和恢复过程中基本无过冲,用于转移的电子开关(比如IGBT)在开关过程中过电压小,可靠性高,吸收电路容易实现。该方案可以很好地替代传统的弧流电源打坑电路。     

具有不同临界电流的Bi2223/Ag多芯超导带材的自场损耗和交流电流电压特性

对具有不同临界电流的Ｂｉ２２２３／Ａｇ多芯超导材的交流电流电压特性进行了测量和评价,当传输电流的有效值Ｉｎｎｓ小于临界电流Ｉｃ时,交流电压的大小与传输电流的频率成正比;但Ｉｎｎｓ接近临界电流时,不同频率所对应的交流电压的大小之间的差别减小了,所有的曲线都汇聚成一条曲线,传输电流的频率分别为４０Ｈｚ,６０Ｈｚ,８０Ｈｚ,２００Ｈｚ及３００Ｈｚ时,我们测量了交变传输电流在Ｂｉ２２２３／Ａｇ带材中产生的自场损耗。结果表明当传输电流的频率较低时,实验结果与基于Ｂｅａｎ模型的Ｎｏｒｒｉｓ方程预期的结果一致;另外,实验结果表明存在一个电流Ｉ′,它的值小于任何一个样品的临界电流,本实验中Ｉ′的值是１０安培,在传输相同大小的电流Ｉｎｎ且Ｉｎｎｓ〈Ｉ′时,Ｂｏｉ２２２３／Ａｇ带材的交流损耗与它的临界电流成正比;但当Ｉｎｎｓ〉Ｉ′     

Theory of current-driven domain wall motion: spin transfer versus momentum transfer

A self-contained theory of the domain wall dynamics in ferromagnets under finite electric current is presented. The current has two effects: one is momentum transfer, which is proportional to the charge current and wall resistivity (rho(w)); the other is spin transfer, proportional to spin current. For thick walls, as in metallic wires, the latter dominates and the threshold current for wall motion is determined by the hard-axis magnetic anisotropy, except for the case of very strong pinning. For thin walls, as in nanocontacts and magnetic semiconductors, the momentum-transfer effect dominates, and the threshold current is proportional to V(0)/rho(w), V0 being the pinning potential.     

等离子体在任意强度的直流电场中产生电流的过程

通过Fokker-Planck模拟,研究了等离子体在任意强度的直流电场中产生电流的过程以及电子分布函数的演变过程.研究发现,不同强度的电场中等离子体的行为存在着明显的差别.在弱电场中,电流与电场满足Spitzer公式,且电流产生的响应时间约等于撤销电场后电流衰减的弛豫时间;在中等强度的电场中,电子分布函数呈现为静止Maxwell分布和漂移Maxwell分布之和,而且在中等强度或者强直流电场中弛豫时间也将远远大于响应时间.根据电子分布函数的演变规律,推导了一组类似于流体力学方程的公式,这组方程像Spitzer公式一样简便地描述了等离子体中电流与电场的关系,并且对电场强度没有限制.数值模拟显示这组方程比Spitzer公式更适用于等离子体的混合粒子模拟中. 关键词： 等离子体电流 电子分布函数 Fokker-Planck模拟 Spitzer公式     

Simulations of V-I characteristics in a plasmafocus fun

The voltage and current characteristics in a plasma focus gun are simulated to yield the current efficiency and the rundown velocity of the current sheath. Since the discharge circuit is strongly influenced by the rundown dynamics of the current sheath, the simple snowplow model, which is modified to include the time-varying current and mass efficiencies, us used. The computer simulations are carried out for two separate experiments using deuterium and argon gas. A steady state of constant rundown velocity and saturated sheath current for both gases is correlated to the maximum holding voltage of the glass insulator. As much as 27% of the total discharge current for the deuterium gas and 33% for argon gas stay behind as leakage currents around the glass insulator when the radial compression phase begins     

Properties of monolithic integration of a resonant tunneling diode and a quantum well laser

An investigation of the electrical and optical characteristics of a resonant tunneling diode monolithically integrated with a quantum well laser is carried out. An analytic expression for the propagating model current is given in terms of the total spontaneous emission rate. The laser is pumped by the current emitted by the resonant tunneling diode. When the current in the laser exceeds the threshold current, laser light is produced. Since the current in the laser exhibits negative differential resistance similar in behavior to the current of a resonant tunneling diode, a bistable light output can be obtained from this new device.     

Current dynamics during disruptions in large tokamaks

Self-consistent modeling of the evolution of the plasma current during disruptions in large tokamaks is presented, taking into account both the generation of runaway electrons and their backreaction on the electric field. It is found that the current profile changes dramatically, so that the postdisruption current carried by runaway electrons is much more peaked than the thermal predisruption current. Although only a fraction of the thermal current is converted into runaway electrons, the central current density increases significantly for typical parameters in JET and ITER. It is also shown that the radial runaway profile can easily become filamented in the radial direction.     

Steady-state fully noninductive current driven by electron cyclotron waves in a magnetically confined plasma

A steady-state, fully noninductive plasma current has been sustained for the first time in a tokamak using electron cyclotron current drive only. In this discharge, 123 kA of current have been sustained for the entire gyrotron pulse duration of 2 s. Careful distribution across the plasma minor radius of the power deposited from three 0. 5-MW gyrotrons was essential for reaching steady-state conditions. With central current drive, up to 153 kA of current have been fully replaced transiently for 100 ms. The noninductive scenario is confirmed by the ability to recharge the Ohmic transformer. The dependence of the current drive efficiency on the minor radius is also demonstrated.     

HLS bunch current measurement system

Bunch current is an important parameter for studying the injection fill-pattern in the storage ring and the instability threshold of the bunch, and the bunch current monitor also is an indispensable tool for the top-up injection. A bunch current measurement (BCM) system has been developed to meet the needs of the upgrade project of Hefei Light Source (HLS). This paper presents the layout of the BCM system. The system based on a high-speed digital oscilloscope can be used to measure the bunch current and synchronous phase shift. To obtain the absolute value of bunch-by-bunch current, the calibration coefficient is measured and analyzed. Error analysis shows that the RMS of bunch current is less than 0.01 mA when bunch current is about 5 mA, which can meet project requirement.

     

Space-charge limiting current in spherical cathode diodes

The results of the investigation on the space-charge limiting current for a spherical-cathode diode in the nonrelativistic situation are presented in this paper,The results show that the current enhancement factor equals the square of E-field enhancement factor on the cathode surface,The generated space-charge limiting current is deduced.In the case of a pin-shaped-cathode diode,the space-charge limiting current is also obtained.Indicating that the current is independent of the geometric paramters of the diode.Analyses of the shielding effects and the conditions for generation of the uniform space-charge limiting beam show that ,for pin-arrayed cathodes,the distance between pins should be in the range from 1.2D to 1.5D.where D is the distance between the two electrodes.     

Study on the current bistability and hysteresis in resonant-tunneling structures

We present a time-dependent quantum-kinetic study for the non-equilibrium electron transport properties of double-barrier resonant-tunneling devices. The approach is based on a self-consistent solution of Wigner equation and Poisson equation. We find intrinsic current fluctuations around the current turning point. These instabilities lead to three current irreversible regions, two current hystereses and one small inverse current change in the valley position of current, for the forward and backward bias sweep. The bias step applied on the device affects the width of each current irreversible regions and the current peak height of the middle region.