On the mechanism of liquid metal ion sources

We have developed a theoretical model of liquid metal ion source operation which consistently explains the shape and size of the ion emitting region, the mechanism of ion formation and properties of the ion beam. We find that field evaporation is the main current generating mechanism and that field evaporation and subsequent postionization produce the doubly and higher charged ions. Field ionization of thermally evaporated neutrals may make a significant, but not dominant, contribution to the current of singly charged ions. Our model is consistent with experimental results on energy spread, energy deficit and charge state ratios and we are able to explain the stability of the emitted ion current.     

Ecton mechanism of the vacuum arc cathode spot

A new mechanism for the operation of a cathode spot in a vacuum arc, based on ecton processes, is proposed. An ecton is formed by the explosion of the tip of a jet of molten metal as it interacts with plasma. The time of ecton operation is assumed to be limited by the thermal conductivity of the liquid metal. For copper electrodes, the theoretical expressions are derived for the specific mass removal, ion erosion characteristics, current density, and the diameters of craters. The results agree well with the experimental data available     

Fabrication and characterization of 1.55 μm single transverse mode large diameter electrically pumped VECSEL

We report on the design, fabrication, and characterization of InP-based 1.55 μm wavelength large diameter (50 μm) electrically pumped vertical external cavity surface emitting lasers (EP-VECSELs). The hybrid device consists of a half vertical cavity surface emitting laser (1/2-VCSEL) structure assembled with a concave dielectric external mirror. The 1/2-VCSEL is monolithically grown on InP substrate and includes a semiconductor Bragg mirror and a tunnel junction for electrical injection. Buried (BTJ) and ion implanted (ITJ) tunnel junction electrical confinement schemes are compared in terms of their thermal and electrical characteristics. Lower thermal resistance values are measured for BJT, but reduced current crowding effects and uniform current injection are evidenced for ITJ. Using the ITJ technique, we demonstrate Room-Temperature (RT) continuous-wave (CW) single transverse mode laser operation from 50-μm diameter EP-VECSEL devices. We show that the experimental laser optical output versus injected current (L–I) curves are well-reproduced by a simple analytical thermal model, consistent with the thermal resistance measurements performed on the 1/2-VCSEL structure. Our results indicate that thermal heating is the main mechanism limiting the maximum CW output power of 50-μm diameter VECSELs, rather than current injection inhomogeneity.     

Magnetodynamic submicrosecond current interrupter

The feasibility of using a magnetodynamic current interrupter for switching multimegaampere current pulses is considered. The operation of the interrupter is based on the fast buildup of edge instabilities. A technical solution is suggested, and the performance of the interrupter when used in the second stage of peaking the current of helical explosive magnetic generators (HEMGs) and capacitor banks is predicted. It is shown by computer simulation that the interrupter can operate in the submicrosecond range and switch currents as high as several tens of megaamperes, the operating speed of the interrupter increasing with linear current density. The limit actuation time of the interrupter may be on the order of 100 ns. A prototype of the interrupter is experimentally verified on a capacitor setup by switching currents with an amplitude of 4.3–4.5 MA.     

硅外延平面二极管过流振荡机理

描述了小空间尺度下一种硅外延平面二极管过流时的实验现象,以电压调控开关的模型解释这种现象。通过电压调控开关模型的二极管间隙间电势变化过程的定性分析可知,由于空间电荷效应,超过或临界空间电荷时,二极管电流有可能呈现振荡特性。通过无限大空间内薄束漂移的时间行为证明了这种振荡存在的可能性。用非线性方程的数学模型对这种现象做了仿真,仿真结果与实验现象相吻合。     

强流脉冲电弧作用下石墨电极蒸发特性

气体开关电弧的热侵蚀作用是电极损耗的主要成因。石墨电极在电弧作用下发生蒸发并在多次放电后有明显的质量损耗,改变了开关内的气体环境和电极间距,导致开关动作可靠性降低。为研究石墨电极在脉冲电弧冲击下的侵蚀特征,基于开关电弧瞬态扩散特征和石墨材料参数,在弧根区域建立了电弧-电极能量耦合模型,得到了等离子体-固体区域的传热特性。考虑石墨电极的相变特征,计算瞬态热作用下石墨电极的加热范围以及临界相变点,研究瞬态电弧热冲击作用下的石墨电极相变机制。研究结果表明,电弧-电极界面热流主要集中在电弧接触面中心,电弧沉积的能量密度最高可达109 W/m2,石墨在电流上升初期基本处于加热状态,在能量积聚作用下,石墨转变为升华状态,传热强度随半径急剧衰减,蒸发区域略小于电弧半径。通过实验记录了5种开关工况下石墨电极烧蚀形貌和质量损失情况,结果表明,电极质量损失与电弧沉积在电极表面的能量线性相关,近似为0.015 mg/J。研究了电弧关键参数对电极质量损失速率的影响,为延缓电极损耗提供数据支撑。     

直流转辙机智能故障测试仪的研究与设计

为了对飞行遥测数据进行实时处理,以Qt为软件开发平台,采用直接接收宽带遥测接收机（RTR）发送的网络遥测数据包的方法,结合机载测试系统的采集格式、参数测试信息、校准信息和ICD信息,完成遥测数据的实时解算、工程量转换和原始数据保存,同时将关心的参数物理量通过网络实时的发送给客户端监控软件,以供试飞工程师进行实时监控。实际试验试飞结果表明,此软件运行稳定和数据准确可靠,完全满足实时监控的需求,具有良好的实用性和发展前景。     

毛细管放电类氖氩69.8nm激光增益特性研究

建立了计算69.8nm激光增益系数的理论模型,根据实验参数,计算了在主脉冲电流为12 kA时,69.8nm激光增益系数最大值为0.32 cm~(-1).理论模拟了不同初始气压下增益系数在毛细管径向上的分布情况.对理论结果的分析表明,最佳的初始气压在12—14 Pa范围内,此时69.8nm激光增益系数的极值最大.实验上,利用毛细管放电装置和罗兰光谱仪,测量了不同气压下的69.8nm激光强度,实验确定的最佳气压为16 Pa,与理论结果相近.此外,实验测量的增益系数(0.4 cm~(-1))略高于理论计算的增益系数(0.32 cm~(-1)).     

多间隙气体开关电感

介绍了一种用于快脉冲直线变压器的低电感多间隙气体开关。专门构造了多种形式的单通道放电实验,测量了在不同形态单通道放电时的开关电感,研究发现:单通道放电时开关电感除了受到角向电流的影响,还与电弧通道引起的放电回路面积变化有关,开关电感理论计算值与单通道放电时的实测结果最接近;开关在自放电和触发时,均形成了多通道放电,电感明显降低,触发时开关电感最小约为49 nH,电极角向电流的影响可以忽略。     

Universal properties of the nonadiabatic acceleration of ions in current sheets

The electric-field-induced acceleration of ions in current sheets in a collisionless plasma is investigated. The analysis of nonadiabatic ion dynamics provides a universal property of the ion acceleration mechanism, which is independent of the magnetic-field model and the initial particle distribution function. The width of the resonance region is estimated. The theoretical results are compared with the experimental and numerical simulation data.     

Temporal criterion for single-frequency operation of passively Q-switched lasers

An analytical expression for the difference in buildup time between two longitudinal modes in a passively Q -switched laser resonator is developed and compared with experimental laser data. The results support the following temporal criterion for single-frequency, passively Q -switched operation: The difference in buildup time between any two longitudinal modes of the laser resonator should be comparable with or greater than the laser pulse duration to ensure single-frequency operation.     

高电压大电流晶闸管组件的热特性

晶闸管具有控制特性好、寿命长、噪声小等优点,目前在脉冲功率技术应用中,利用大功率晶闸管代替传统气体开关是研究趋势。晶闸管在高电压、大电流、重复频率工作条件下使用,需要对开关组件进行仔细的选型和组合。基于晶闸管的失效机理,对晶闸管组件在高电压、大电流、高di/dt,高du/dt、重复频率工作下的发热问题进行了理论分析、仿真计算和试验研究,对晶闸管组件在重复频率脉冲功率系统中的使用条件给出了理论依据。随着晶闸管工作电压、电流、频率增大,晶闸管的热损耗也越大,晶闸管的发热也越严重。为保证晶闸管安全稳定地工作,需要结温保持在安全范围内,不能长时间在重复频率下工作。     

Concerning microsecond megaampere-current plasma opening switches

The operation mechanism of a microsecond megaampere-current plasma opening switch is considered. The magnetic field penetrates into the plasma via near-electrode diffusion. The increase in the degree of plasma magnetization due to electron heating results in an increase in plasma resistivity and current break. The problem of calculating a plasma opening switch is mathematically formulated. The problem reduces to simultaneously solving one-fluid two-temperature MHD equations with allowance for the Hall current and two-dimensional electric circuit equations. To analyze the solution obtained, one-dimensional equations are derived based on the assumption that the size of the electrode region in which the plasma is strongly magnetized is much smaller that the plasma column length. In this approximation, the operating modes of a plasma opening switch are studied numerically. On long time scales (≥2–3 μs), the operation is limited by plasma ejection from the interelectrode gap. On short time scales (≤1 μs), the dominant process is the penetration of the magnetic field with the current velocity. The results of the calculations are compared with the available experimental data. The developed concept and numerical procedure are used to optimize the scheme for an explosion experiment on breaking megaampere currents under conditions similar to those in the EMIR complex.     

Experimental investigation of the conduction phase of themicrosecond plasma opening switch

Results of experimental studies of the conduction phase of the microsecond plasma opening switch are presented. It is shown that during this phase, translation of the current channel in the plasma near the anode takes place with anomalously high velocity. The ion component of the current reaches 25-30% of the total value, and the current streamlines late in the conduction phase acquire a considerable slant in the axial direction. The ion current behind the current channel makes up more than 30% of the total current there. The ion current density reaches a maximum during the conduction phase and decreases slowly during switching     

AlInGaAs垂直谐振腔顶面发射半导体激光器横向温度效应的解析热模型及其表征

依据增益导波垂直谐振腔顶面发射半导体激光器热区特点与室温连续波运行条件建立了一个优化的全解析热模型，对AlInGaAs/AlGaAs垂直谐振腔激光器的横向温度效应进行了详细的解析计算分析，其完全的解析表达展示了更加清晰的横向热场物理图像，对于器件内部热场变化规律的理论预期与实验结果完全符合. 该解析模型及其结果对于研究热稳态下的垂直谐振腔激光器热动力学特性，优化器件结构和控制激光器的阈值电流与功率温度饱和效应，特别是二维面阵器件中的横向热叠加效应提供了一个有用的工具. 关键词： 半导体面发射激光器 热效应 解析计算模型.     

Current state of photoconductive semiconductor switch engineering

This paper presents the current state of a photoconductive semiconductor switch engineering. A photoconductive semiconductor switch is an electric switch with its principle of operation based on the phenomenon of photoconductivity. The wide application range, in both low and high-power devices or instruments, makes it necessary to take design requirements into account. This paper presents selected problems in the scope of designing photoconductive switches, taking into account, i.e. issues associated with the element trigger speed, uniform distribution of current density, thermal resistance, operational lifespan, and a high, local electric field generated at the location of electrodes. A review of semiconductor materials used to construct devices of this type was also presented.     

MV级重复频率三电极气体开关的优化研究

 对一种高工作电压、高重复频率的三电极气体开关的优化设计方法进行了研究,包括绝缘结构的优化、最优触发孔径和触发电极位置的选取。采用设计开关开展了实验研究,并对实验结果进行了分析。结果表明,开关实现了工作电压1.1 MV,峰值电流约13.8 kA,重复频率100 Hz的最大稳定运行参数,性能满足设计要求;开关绝缘恢复性能良好,各次电压波形幅值均匀,分散性小,归一化标准偏差小于3%。     

Plasma density evolution in plasma opening switch obtained by a time-resolved sensitive He-Ne interferometer

To understand the formation process of vacuum gap in coaxial microsecond conduction time plasma opening switch (POS), we have made measurements of the line-integrated plasma density during switch operation using a time-resolved sensitive He-Ne interferometer. The conduction current and conduction time in experiments are about 120 kA and 1 μs, respectively. As a result, more than 85% of conduction current has been transferred to an inductive load with rise time of 130 ns. The radial dependence of the density is measured by changing the radial location of the line-of-sight for shots with the same nominal POS parameters. During the conduction phase, the line-integrated plasma density in POS increases at all radial locations over the gun-only case by further ionization of material injected from the guns. The current conduction is observed to cause a radial redistribution of the switch plasma. A vacuum gap forms rapidly in the plasma at 5.5 mm from the center conductor, which is consistent with the location where magnetic pressure is the largest, allowing current to be transferred from the POS to the load.     

Induced current of high temperature superconducting loops by combination of exciting coil and thermal switch

With its commercialization, the second-generation (2G) high temperature superconducting (HTS) RE—Ba—Cu—O (REBCO, RE is rare earth) tape is extensively applied to the superconducting magnets in the high magnetic fields. However, unlike low temperature superconducting (LTS) magnets, the HTS magnet cannot operate in the persistent current mode (PCM) due to the immature superconducting soldering technique. In this paper, an exciting method for two HTS sub-loops, so-called charging and load loops, is proposed by flux pump consisting of exciting coil and controllable thermal switch. Two HTS sub-loops are made of an REBCO tape with two slits. An exciting coil with iron core is located in one sub-loop and is supplied with a triangular waveform current so that magnetic field is generated in another sub-loop. The influence of magnetic flux on induced current in load loop is presented and verified in experiment at 77 K. The relationship between the induced magnetic flux density and the current on the sub-loops having been calibrated, magnetic flux density, and induced current are obtained. The results show that the HTS sub-loops can be excited by a coil with thermal switch and the induced current increases with magnetic flux of exciting coil increasing, which is promising for persistent current operation mode of HTS magnets.     

X-Ray Measurements during Whistler-Mode Electron Cyclotron Resonance Plasma Startup and Heating in an Axisymmetric Magnetic Mirror

New measurements and analyses of whistler-mode electron cyclotron resonant heating (ECRH) startup and heating in an axisymmetric magnetic mirror are presented. Experimental studies of startup are presented which include the effects of initial neutral gas pressure on density and energy buildup rates, the effects of electron-beam-generated seed plasma on startup times, and a possible density threshold for the absolute whistler instability. Results of two types of analyses are presented. The first is a Fokker-Planck finite-element simulation the principal result of which is the prediction of the creation of a sloshing electron velocity distribution in the first 10 ?s after microwave power is applied. The second simulation uses rate equations to predict buildup, with rate coefficients based on a model sloshing-electron distribution function. Both results are consistent with experimental observations. Measurements of X-ray emission provided information about plasma transport, the sloshing electron spatial distribution, and the hot-electron average energy. The foil ratio technique gave average energies of 1-3 keV during whistler-mode ECRH, in agreement with afterglow measurements of hot electron decay. Possible applications of whistler-mode ECRH plasma production and heating are for plasma soft X-ray sources and plasma potential modification in tandem mirror machines.