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.     

Effect of structure doping profile on the current switching-off process in power semiconductor opening switches

Using a physicomathematical model, the process of current breaking in power semiconductor opening switches was investigated in p ⁺-p-n-n ⁺ structures with different doping profiles. The model takes account of the actual doping profile of a structure, diffusion and drift of current carriers in a strong electric field, recombination via deep impurities and Auger recombination, and impact ionization in a dense plasma. The calculation of the electrical circuit of an opening switch is based on solution of Kirchhoff’s equations. It has been shown that in the nanosecond regime of breaking superhigh current densities with densities of the interrupted currents from a few to tens of kA/cm², the dominant factor in the current breaking process is the width of the p-region in the initial doping profile of a structure. An increase in the p-region width from 100 to 200 μm makes the velocity of the excess plasma front propagating in the p-region in the reverse pumping stage higher by a factor of 5–7. Higher propagation velocity of the plasma front makes the current breaking process more intensive, which is manifested in the shorter current breaking time and higher overvoltage across the opening switch.     

等离子体断路开关的一维磁流体力学数值模拟

 采用磁流体力学的方法对等离子体端路开关进行了一维数值模拟，通过对给定的进入等离子体的电流波形模型的计算，给出了轴向上等离子体的运动及其不同时刻的密度分布，分析了磁场在等离子体内部的异常渗透过程，指出考虑Hall效应是产生这一异常现象的最为主要的因素。     

Operation of microsecond plasma opening switches

Closing and breaking of current in microsecond megaampere plasma opening switches are considered. Conductivity current scaling in the switch due to plasma acceleration by a magnetic piston is discussed and compared with experimental data. Two ways of determining the width of a current channel are taken up. This channel results from the diffusion of the magnetic field in the plane of the piston followed by the convective ejection of the field “frozen” in the accelerated plasma flow behind the shock wave into the bridge. Based on experimental data, a scaling law for the voltage on the switch according to the switch parameters is derived. The problem of reverse closing, which limits the efficiency of storage energy extraction into the load, is considered.     

能量输运对柱状等离子体开关磁场穿透过程的影响

 对于高密度、导通时间为μs级的柱状等离子体开关，利用磁流体动力学理论(MHD)，对其导通阶段的磁场穿透过程进行了模拟，得到了磁场分布随时间的变化；研究了开关导通过程中能量输运导致的温度不均匀分布对磁场穿透过程的影响。模拟结果表明：对于高密度等离子体开关，磁场以远大于磁扩散速率的速度穿透到等离子体中；在磁压对等离子体产生的压缩效应和欧姆加热效应共同作用下，激波区域的等离子体温度显著升高，这进一步加速了磁场穿透；当考虑能量输运方程时，开关导通时间为0.87 μs，比等温模型的结果0.92 μs短，与实验结果0.87 μs相一致。     

The Jon Beam Opening Switch

Plasma opening switches (POS's) have shown excellent characteristics in pulsed power applications. Proposed POS scaling predicts that the fastest opening time for a given conducted current should occur using a high-velocity low-density plasma as the switch medium. The ion beam opening switch (IBOS) uses a charge-neutral ion beam of 100-300 kV, ? 120 A/cm2 as the switch "plasma." Its velocity of up to 600 cm/?s and density of ~1012/cm3 make this a very fast low-density plasma compared with typical 10 cm/?s and 1013/cm3 POS plasmas. The IBOS has conducted ? 70 kA flowing in a parallel-plate transmission line driven by a 4-? pulser. IBOS opening time is load dependent, being ? 4 ns into a 15-nH load and about twice as long into a 4-? electron diode load. However, switch impedance is not zero during the entire conduction time, rising to ? 3 ? by the time of peak current. Peak current conducted before opening does not vary linearly with either injected ion current or switch axial length. Instead, the conduction current scales with plasma density in the switch, and is nearly independent of switch area until the area is restricted to a narrow (~1 cm) strip.     

Scaling microsecond-conduction-time plasma opening switch operationfrom 2 to 5 MA

We describe experiments in which conduction currents were successfully scaled from 2 to 5 MA for conduction times around 1 μs in a coaxial geometry plasma opening switch (POS) on the 4 MJ ACE 4 driver. Simple models of POS operation, derived from previous work, were used to scale successful results from drivers that operate at microsecond conduction times, but at currents below 1 MA. An MHD model for the conduction phase was verified in which the square root of the plasma density is approximately proportional to the product of conduction time and peak conduction current divided by the switch radius and length. For the opening phase, a model where the POS gap is approximately constant when the local plasma conditions at the beginning of the conduction phase are kept roughly the same is consistent with the observed POS opening voltages of at least 1 MV. The conduction current was increased by increasing the POS cathode radius from 6 to 20 cm while maintaining roughly the same plasma density. This increase in radius resulted in the observed increase in the conduction-current/conduction-time product from 2 to 5 MA μs while maintaining MV POS voltages     

A Self-Similar Model for Conduction in the Plasma Erosion Opening Switch

The conduction phase of the plasma erosion opening switch (PEOS) is characterized by combining a 1-D fluid model for plasma hydrodynamics, Maxwell's equations, and a 2-D electron-orbit analysis. A self-similar approximation for the plasma and field variables permits analytic expressions for their space and time variations to be derived. It is shown that a combination of axial MHD compression and magnetic insulation of high-energy electrons emitted from the switch cathode can control the character of switch conduction. The analysis highlights the need to include additional phenomena for accurate fluid modeling of PEOS conduction.     

带辅助磁场等离子体断路开关的数值模拟

 利用全电磁网格粒子方法模拟了外加磁场对等离子体断路开关（POS）断路性能的影响，给出了电压倍增系数与外加磁场的关系曲线。数值模拟表明，外加轴向磁场线圈必须放在同轴型POS阴极的同侧才能显著改善开关的断路性能；当外加角向磁场时，内电极为阴、阳极的同轴型POS的断路性能都得到了不同程度的改善。随着外加磁场的增大，电压倍增系数将达到饱和。     

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。     

A long conduction time compact torus plasma opening switch

Experiments to form and accelerate compact toroid (CT) plasmas have been performed on the 0.4-MJ Shiva Star fast capacitor bank at Phillips Laboratory. Theoretical investigations of employing a CT as a very fast opening switch are reported. A particular axisymmetric, geometrically complex switch design is studied with the help of 2-1/2-dimensional magnetohydrodynamic computer simulations. This design, called a magnetically-confined-plasma opening switch (McPOS), accumulates magnetic energy in an inductive store. Because of its intrinsic stability, the switch can conduct current for ten or more microseconds and can open in less than 100 ns-substantially less than the risetime of the capacitively produced electric current. A long conduction time compact torus plasma opening switch     

Experiments on the GIT-4 with the load connected upstream of the plasma opening switch

Experiments have been performed on the GIT-4 generator with a plasma opening switch to study the operation of a circuit connecting the load and the switch through an untriggered spark gap depending for its operation on a discharge over the surface of a dielectric in vacuum. The current switching into inductive loads of different inductance was investigated. The dependence of the time the switch is open on load inductance has been found. It has been demonstrated that the surface-discharge spark gap can be used at current rise rates of up to ∼2·10¹³ A/s. Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 31–35, December, 1999.     

High-Power Opening-Closing Switches Using Grid-Controlled Plasmas

Two switches are described with the capability of rapidly interrupting high-power circuits: a vacuum triode with a large-area plasma cathode, and a grid-controlled plasma conduction switch. Theoretical models for the vacuum triode imply that it could control voltages in the range ?100 kV at current density ?2 × 104 A/m2. The vacuum switch has the advantage of rapid switching at the expense of reduced efficiency because of its significant anode-cathode voltage drop. In contrast, the plasma switch has almost zero voltage in the conducting state. The theoretical models presented indicate that the plasma switch could conduct current densities in the range 10 × 104 A/m2 with open-circuit voltage ? 100 kV. Although the closing time is long (~1 ?s), the predicted opening time is short (~20 ns). Initial experiments demonstrating the principle of operation of the plasma switch are reported.     

Ionization formation of plasma inhomogeneity by the near-zone field of a magnetic-type source in a magnetized plasma

An investigations is made of the steady-state structure of a plasma inhomogeneity arising as a result of high-frequency heating and additional ionization of a background magnetized plasma by the near-zone field of a magnetic-type source (ring electric current). It is assumed that the source axis is parallel to an external magnetic field; the source frequency belongs in the low hybrid band. The main attention is focused on the particular case (important for possible applications) when the characteristic longitudinal and transverse scales of density distribution considerably exceed the corresponding scales of distribution of the electron temperature and of the source field. Simplified equations for the near-zone field of the source, the electron temperature, and the plasma density are written for this particular case. Based on the numerical solution of these equations, steady-state distributions of plasma parameters in the formed plasma inhomogeneity are found. It is demonstrated that a plasma inhomogeneity proves to be markedly extended along the external magnetic field. It is found that, for the values of the source current that are attainable under the conditions of active ionospheric and model laboratory experiments, the maximum plasma density in a nonuniform plasma may appreciably exceed the background value.     

Plasma erosion opening switch using laser-produced plasma

In order to construct a practical inductive energy storage pulsed power generator, an opening switch which can repeatedly conduct a large current and then rapidly interrupt this current is necessary. Though the plasma erosion opening switch (PEOS) can interrupt a large current rapidly, the effective number of switch operations is limited because of the decrease of the carbon sprayed on the insulator with each shot. A PEOS using a laser-produced plasma, which can possibly be operated for hundreds of thousands of shots without maintenance, is proposed, and its operation as an opening switch is confirmed experimentally     

高密度等离子体融断开关融蚀现象的粒子模拟研究

 利用自行研制的2.5维全电磁柱坐标粒子模拟程序对高密度等离子体融断开关融断区域中的融蚀现象进行了模拟研究,详细地介绍了计算模型的建立以及复杂边界的算法处理。模拟结果表明在融断开关导通电流的最后阶段,由于磁压力、磁场渗透作用和非中性静电融蚀作用,在融断区域的阴极附近会形成一定宽度的真空鞘层。由于等离子体密度的下降以及初始真空鞘层的存在,使得即使只有较小的离子电流,融蚀机制也完全可以导致PEOS最终断开。     

Plasma-opening-switch-based repetitive generator

Operation peculiarities of the RS-20 generator based on the plasma opening switch (POS) including its repetitive operation capabilities are reviewed. They are: limited current value, gas emission, pulsed heat loads, etc. The feasibility of a POS with maximum impedance and relatively low (100 kA and lower) drive current is being investigated. The evolution of the POS design used in the repetitive X-ray generator RS-20 is presented in various schemes. The “reflecting” scheme has a variable anode transparency in the direction of the load and another scheme uses an external pulsed magnetic field. The paper describes a combined X-ray converter having a multilayer structure: a thin layer of fine-grained tungsten is placed between two layers of carbon film. The progress achieved in improvement of the RS-20 main units (Marx Generator, Plasma Opening Switch, X-ray Converter) made it possible to increase their lifetime to more than 10⁷ pulses without replacement     

Investigation of plasma opening switch conduction and openingmechanisms

Plasma opening switch techniques have been developed for pulsed power applications to exploit the advantages of electrical energy storage in a vacuum inductor compared to conventional, capacitive-based energy storage. Experiments are described that demonstrate the successful application of these techniques in conduction time ranges from 50 ns to over 1 μs. Physics understanding of the conduction and opening mechanisms is far from complete; however, many insights have been gained from experiments and theory. Measurements of current distribution, plasma density, and ion emission indicate that conduction and opening mechanisms differ for the 50 ns and 1 μs conduction times. For the 50 ns conduction time case, switching begins at a current level close to the bipolar emission limit, and opening could occur primarily by erosion. In the 1 μs conduction time case, limited hydrodynamic plasma displacement implies far higher plasma density than is required by the bipolar emission limit. Magnetic pressure is required to augment erosion to generate the switch gap inferred from experiments     

240 kJ模块化能库型脉冲放电电源研制北大核心CSCD

空间等离子体环境模拟与研究装置用于在地面模拟空间磁场和等离子体环境,需要在3.5μH电感、0.8 mΩ电阻的环向场线圈负载上产生前沿130μs、降流时间不大于1600μs、峰值260 kA的脉冲电流,因此设计了一套模块化的电容器型放电电源。针对相对较小电感的负载,根据设计要求的放电波形和开关组件通流能力,考虑负载短路故障的情形,给出了保护电感、优化的模块数量等回路参数计算方法。进一步采用传输电缆作为能量传输,同时将电缆寄生电感作为保护电感的方案,研制了一套由4个模块组成的放电电源。研究结果表明,本文给出的电路理论计算结果与设计要求一致,放电试验进一步证明电源设计满足设计放电波形要求。     

Plasma Erosion Opening Switch in the Double-Pulse Operation Mode of a High-Current Electron Accelerator

This paper reports the results of investigations of the operation of a fast current opening switch, with a 1013-1016 plasma density produced either by dielectric surface flashover or by explosive emission of graphite. A series of two pulses was applied to two diodes in parallel. The first pulse produced plasma in the first diode which closed that diode gap by the arrival time of the second pulse. The first, shorted, diode then acted as an erosion switch for the second pulse. A factor of 2.5-3 power multiplication was obtained under optimum conditions. The opening-switch resistance during the magnetic insulation phase, neglecting the electron losses between the switch and the generating diode, exceeded 100 ?. The duration of the rapid opening phase was less than 5 ns under optimum conditions. This method of plasma production does not require external plasma sources, and permits a wide variation of plasma density, which in turn allows high inductor currents and stored energies.