The Application of a Plasma Erosion Opening Switch to a Nanosecond Generator at the Power Level of 1010 W

This paper is devoted to experimental studies of a short-pulse (80 ns) inductive system with a coaxial plasma erosion opening switch (PEOS), operating at the 2-5 × 1010 W level. Scalings of the PEOS and ion diode characteristics with different parameters (PEOS plasma density and velocity, PEOS electrode geometry, load impedance, type and strength of an external magnetic field) were carried out. It was seen that for the most efficient energy and power switching to the load by the PEOS, the following conditions are preferable: high velocity and low density of the plasma flow, negative polarity of the inner PEOS electrode, coincidence of the switch current and injected plasma flow directions, the absence of an external magnetic field, and the presence of an additional self-field in the PEOS region. Power enhancement of a factor of 3 and pulse shortening by a factor of 2 were obtained under optimal conditions.     

Fluid Simulation of the Conduction Phase of the Plasma Erosion Opening Switch

The conduction phase of the plasma erosion opening switch (PEOS) is studied using a 1?-D electromagnetic two-fluid code. The focus of this work is on understanding how two effects, a current-limiting model of electron emission, and the magnetic insulation of electrons at the cathode, determine current conduction in the plasma. Simulations are performed in the parameter regimes of the Gamble I, POP, and PBFA II pulsed power generators, and previous low-density, short-rise time simulations of the PEOS. Fluid code results are compared to a 1-D analytic theory and to the Gamble I and POP experiments. Good agreement between theory and simulation, but mixed agreement between simulation and experiment is found. Experimental B-field measurements on POP show weaker j × B compression than the simulation. Current penetration and plasma current channels qualitatively similar to experimental observation are found in the Gamble I regime. However, magnetic insulation of electrons emitted from the cathode bunches the electron flow into narrower current channels than observed experimentally. In several cases, the presence of an electron-scattering or energy-loss mechanism near the cathode must be invoked to overcome magnetic insulation and widen the current channels.     

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 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.     

Plasma Erosion Opening Switch Research at NRL

This paper is a review of plasma erosion opening switch (PEOS) research performed at the Naval Research Laboratory (NRL). Several experimental and theoretical results are described to illustrate the present level of understanding and the best switching results obtained to date. Significant power multiplication has been achieved on the Gamble II generator, producing 3.5 TW with less than 10-ns rise time. Switching after nearly 1-?s conduction time has been demonstrated on Pawn, producing a 0.2-TW 100-ns pulse. Scaling the switch to higher current, power, and conduction time should be possible based on theoretical analysis and the favorable results of scaling experiments performed thus far.     

等离子体源参数对长导通等离子体断路开关性能的影响

 研制了可工作在长导通时间（约1μs）的等离子体断路开关，实验研究了等离子体源参数，包括等离子体枪与主回路之间的触发延时、等离子体枪的工作电压以及等离子体枪的数目对开关性能的影响规律。研究结果表明，开关导通时间和开关电压随触发延时、枪工作电压和数目的增加而增加，但当开关导通时间接近主回路电流四分之一周期时，开关电压呈下降趋势。当Marx发生器工作电压为120kV且采用4个等离子体枪时，实验获得的最大电压倍增系数约为1.8。     

Implicit Collisional Three-Fluid Simulation of the Plasma Erosion Opening Switch

The plasma erosion opening switch (PEOS) has been studied with the aid of the ANTHEM implicit simulation code. This switch consists of fill plasma injected into a transmission line. The plasma is ultimately removed by self-electrical forces, permitting energy delivery to a load. Here, ANTHEM treats the ions and electrons of the fill plasma and the electrons emitted from the transmission-line cathode as three distinct Eulerian fluids-with electron inertia retained. This permits analysis of charge separation effects, and avoids the singularities that plague conventional MHD codes at low density. E and B fields are computed by the implicit moment method, allowing for time steps well in excess of the electron plasma period ?t >> ?p-1, and cells much wider than a Debye length, ?x >> ?D. Switch dynamics are modeled as a function of the driving electrical pulse characteristics, the fill plasma parameters, and the emission properties of the transmission line walls-for both collisionless and anomalously collisional electrons. Our low-fill-density (ne ? 4 × 1012 electrons/cm3) collisionless calculations are in accord with earlier particle code results. Our high-density computations (ne ? 2 × 1013 electrons/cm3) show the opening of the switch proceeding through both ion erosion and magnetic pressure effects. The addition of anomalous electron collisions is found to diffuse the driving B field into the fill plasma, producing broad current channels and reduced magnetic pressure effects, in some agreement with NRL experimental measurements.     

Computer Simulation of High-Power Ion Beam Generation Using the Plasma Erosion Opening Switch and Microsecond Store Systems

This paper deals with computer simulation of plasma erosion opening switch (PEOS) operation in the context of short-pulse high-power ion beam (HPIB) generation in microsecond store systems. The scaling of PEOS parameters and ion diode characteristics with various operating conditions was determined. The simulations showed the best PEOS characteristics for a hydrogen plasma (i.e., the lowest mass) with a high flow velocity and low density, although for some applications a plasma with A/Z > 1 may be preferable. It was shown that the efficiency of HPIB generation in the diode depends on its location relative to the PEOS, the time delay of anode plasma formation, the use of a spiral electrode in the PEOS region, and the use of an arrangement involving an ion return current bypass through the PEOS region. The optimization of the PEOS and ion diode with coaxial configurations and 100 kJ stored in the 600-kV Marx yielded a 16-percent overall efficiency HPIB generation in the diode, with a diode voltage and power of 4.2 MV and 0.42 TW, respectively.     

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.     

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     

Interferometry of flashboard and cable-gun plasma opening switcheson Hawk

Interferometry of plasma opening switch (POS) plasmas on the Hawk generator has shown many important features of the plasma evolution during conduction and opening. Opening occurs when a low-density region forms at a radial location determined by plasma redistribution during the conduction phase, consistent with J×B forces and the measured plasma distributions produced by the sources alone. High neutral densities have been detected in the POS region during conduction. Low-density plasma appears between the POS and the load at the time current appears in the load, and high-density plasmas appear there later in time. There are two important differences between the density evolution of POS's utilizing flashboard and cable-gun plasma sources. 1) There is a substantial (two-three times) increase in the electron inventory during conduction using cable guns that is not detected using flashboards. This is attributed, primarily, to ionization of ions and neutrals for the cable-gun case. 2) The conduction scaling with plasma density implies that the cable-gun POS has an effective ion mass/charge ratio about double that for the flashboard POS     

Pulsed Power Compression Research by Vacuum Opening Switch at ILE Osaka

The performance of a vacuum fast opening switch in an inductive store pulse compression system was investigated theoretically and experimentally at the Institute of Laser Engineering, Osaka University. A parameter survey for the pulsed power compression system was performed for optimizing the power amplification and efficiency. An analysis of the plasma erosion opening switch (PEOS) showed that a low-density high-injection velocity plasma and a small radius switch is desired for pulse compression. In experiments, the effect of plasma injection velocity and injection polarity on the switch operation was studied on an "inverse pinch" electron beam diode, and high-voltage and high-impedance operation were performed on an ion diode.     

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     

基于SOS和LTD技术的高重复频率脉冲发生器

提出了磁饱和直线变压器驱动源(LTD)泵浦半导体断路开关(SOS)产生高重复频率短脉冲的技术路线。利用LTD初次级线圈为单匝同轴结构和磁芯可饱和的特点,实现快速反向泵浦SOS,通过多级LTD模块叠加获得高电压输出。采用射频金属氧化物场效应晶体管(RF MOSFET)作为LTD初级电路的主开关,将SOS正向泵浦电流脉冲时间降至数十ns,泵浦电流脉冲重复频率最高可达MHz。最终研制出一台基于SOS的10级磁饱和LTD型脉冲发生器,输出电压约11kV,电流220A,脉冲宽度约2ns,重复频率为20kHz。实验验证了磁饱和直线脉冲变压器泵浦SOS产生高重复频率短脉冲的技术路线可行。     

Energetic electron and ion beam generation in plasma openingswitches

In this paper, we present measurements of ion and electron flows in a nanosecond plasma opening switch (NPOS) and a microsecond plasma opening switch (MPOS), performed using charge collectors. In both experiments, an electron flow toward the anode, followed by an ion flow, were observed to propagate downstream toward the load side of the plasma during the plasma opening switch (POS) conduction. In the MPOS, ion acceleration was observed to propagate axially through the entire plasma. These results are in satisfactory agreement with the predictions of the electron magnetohydrodynamics (EHMD) theory and the results of fluid and particle-in-cell (PIC) code simulations. At the beginning of the POS opening, a high-current density (≈2 kA/cm²) short-duration (10-30 ns) axial ion flow downstream toward the load was observed in both experiments, with an electron beam in front of it. These ions are accelerated at the load side of the plasma and are accompanied by comoving electrons. In the NPOS, the ion energy reaches 1.35 MeV, whereas in the MPOS, the ion energy does not exceed 100 keV. We suggest that in the NPOS the dominant mechanism for the axial ion acceleration is collective acceleration by the space charge of the electron beam, while in the MPOS, axial ion acceleration is probably governed by the Hall field in the current carrying plasma     

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.     

Review of Plasma Flow Switch Development

The plasma flow switch utilizes the nonlinear and nonuniform dynamics of a plasma discharge in vacuum to accumulate magnetic energy in times of several microseconds and then release this energy to a load in times of a few hundred nanoseconds. Experiments have been performed with capacitor banks up to 6 MJ, providing currents in excess of 107 A and peak voltages over 0.5 MV. Theoretical models include simple slug dynamics coupled to lumped-circuit analyses, magnetoacoustic considerations of one- and two-dimensional aspects of the plasma flow, and two-dimensional magnetohydrodynamic code calculations. The present article reviews both experimental and theoretical efforts, discusses the use of the plasma flow switch to drive plasma liner implosions and high-energy ion flows, and indicates directions for plasma flow switch applications to very high current, high-energy inductive pulsed power systems.     

100 kA微秒导通时间等离子体断路开关研究

 研制了最大导通电流约为100 kA的微秒导通时间等离子体断路开关,开展了该导通电流下的等离子体断路开关性能实验,得到的负载电流上升时间为54-76 ns,最高开关电压为1.38 MV,最高电压倍增系数达到4.9。建立了导通阶段开关区等离子体运动的二维雪耙模型,初步数值模拟结果表明,该模型对目前开展的实验有较好的预估能力。     

Compact pulsed power generator using an inductive energy storagesystem with two-staged opening switches

The pulsed power generator, named ASO-I, is extremely compact and light in comparison with a conventional pulsed power generator, which consists of a Marx bank and a water pulse forming line. The ASO-I has a two-staged opening switch, consisting of fuses in water and a plasma erosion opening switch, and can be operated hundreds of times a day at an output power of 230 kV and 35 kA. The parallel fuses are effective for power multiplication, and small differences in length of the parallel fuses do not influence the output power. The risetime of current through the short-circuit load decreases with the increase of the gap length of the spark gap, which is placed between the fuses and the load. The plasma erosion opening switch can be operated as a second opening switch, and the risetime of the current through the short-circuit load decreases from 250 to 10 ns. The maximum resistance of the plasma erosion opening switch is 3.5 Ω with an open-circuit load     

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