Pulsed Power Discharge Research Articles

Comparative study of magnetic field effect on fast plasma flow of heavy and light species investigated by spectroscopic measurement

To understand the effects of magnetic fields on the propagating plasma flows of heavy and light ion species, a laboratory-scale experiment was conducted using a pulsed-power discharge. The plasma drift velocity and electron temperature were estimated by time-of-flight and line-pair methods, respectively, using spectroscopic measurements. Ion current waveforms were measured using an ion collector. When a magnetic field was applied, the plasma drift velocity decreased and the electron temperature increased in both heavy and light plasmas. The magnetic Reynolds number, pressure balance between the plasma and magnetic field, and ion current waveforms show that heavy plasma has a high possibility of deforming the magnetic field and generating accelerated ions through interaction with the magnetic field.

Failure mechanisms of the thyristor switch in pulsed arc electrohydraulic discharges

In order to study the failure mechanism of the thyristor switch in the application of electric pulse fracturing, an underwater pulse power discharge experimental platform was built, the impedance characteristics of the plasma channel were analyzed and the circuit equivalence was carried out for each discharge stage. Then, based on the Silvaco simulation software, a theoretical thyristor model was established. By observing the distribution of the internal carriers and current density, the turn-on and turn-off processes of the thyristor switch under high voltage were analyzed. The formation factors of peak voltage in the turn-off process were studied, the easy breakdown position was pointed out, and a method to suppress the reverse peak voltage by creating critical damping oscillations in the discharge circuit was proposed. Finally, a pulsed power discharge experiment was carried out to verify the theoretical analysis. The experimental results show that the discharge waveform conforms to the theoretical analysis, and the high voltage breakdown damage of the thyristor is also consistent with the theoretical simulation model. Furthermore, the proposed thyristor protection method can greatly suppress the reverse voltage spike, reduce the peak voltage by 52%, and effectively avoid the damage caused by withstand voltage breakdown in the application of pulse power discharge.

Development of liquid metal targets for high-repetition intense laser and pulsed-power discharge applications

In this study, we investigate the response of linear liquid metal flow to a magnetic field when used as a load for high-repetition pulsed-power discharges and as a sheet for a laser target. When a magnetic field was applied perpendicular to the liquid metal flow, the flow deformed while maintaining its thickness. This approach may reduce current and enhance light sources in Z-pinch and alternative X-pinch discharges. However, low-frequency fluctuations were more prominent when the magnetic field was applied parallel to the liquid metal flow in sheet form. These findings suggest that combining liquid metal flow with a magnetic field could effectively facilitate high-repetition pulsed-power discharges and laser operations.

Measurement of Ion Energy Distribution Function of Fast Plasma Flow Driven by Plasma Focus Device Using Retarding Field Energy Analyzer

To understand the mechanism of particle acceleration in collisionless shocks, generating a collisionless plasma flowing through dilute gas is required. We have proposed a compact plasma focus (CPF) device to generate collisionless plasma by using pulsed-power discharge. To discuss a particle acceleration process in collisionless shocks, it is necessary to evaluate an ion energy distribution function (IEDF) of the plasma. In this study, we measured the IEDF of the plasma flow using a retarding field energy analyzer (RFA). The experimental results measured by the RFA showed that ions with a few eV are dominant in the plasma flow generated by the CPF device. The IEDF could be fitted with the shifted Maxwellian distribution. The plasma parameters were estimated to be the ion number density ni = 4.6+−00..28 × 1019 m−3, the ion temperature Ti = 0.8+−00..64 eV, and the drift velocity vd = 11+−03..55 km/s. The estimated velocity approximately agreed with the result of a time-of-flight method calculated by the ion current waveform.

Shock waves in pulsed electrical discharges in liquids: numerical simulation and comparison to experiment

In this paper a computational model for the post-breakdown phase of an electrical discharge in liquids is presented and validated through comparison with data from a high voltage pulsed power discharge in a water-filled crucible. The numerical framework consists of an arc plasma channel modeled by equivalent resistor-inductor-capacitor circuit equations coupled to a computational fluid dynamics (CFD) model (based on OpenFOAM) that solves the compressible fluid equations for describing the shock waves associated with the rapid development of the plasma channel. The circuit model equations evolve the initial discharge plasma expansion which are then used to initialize the pressure pulse in the CFD model. Both single-phase (liquid) and two-phase (gas–liquid) CFD solvers were implemented and compared. The dynamics and magnitude of the simulated pressure pulse perturbations at the boundaries of the crucible were validated with the pressure sensor measurements made in an experiment of a pulsed electrical discharge in liquid water.

QUALITY EVALUATION OF PULSED POWER RECYCLED SAND BY ELECTRICAL RESISTIVITY METHOD

Construction and Demolition (C&D) wastes, inclusively concrete, establishes a major portion of total solid wastes produced in the globe. Regeneration of recycled aggregates from concrete wastes is a promising technique to mitigate the over-exploitation of natural sand and make waste concrete as a source for aggregates. This study mainly discusses the production of recycled fine aggregates from concrete wastes by electric pulsed power discharge method and it’s evaluation with other natural and artificial fine aggregate. Specimens were prepared from both pulsed power recycled sand and virgin sand. The water absorption of pulsed power recycled sand was tested regarding virgin Fine Aggregates (FA) by the electrical conductivity method. The water absorption of recycled sand progressed rapidly during the initial stage of the water absorption test. Besides the pulsed power recycling technique, it is more effective compared to other recycling methods, it produced high-quality fine aggregate with a reduced amount of powder. The compressive and tensile strengths of the mortar produced from pulsed power recycled sand were also approximately identical to mortar made of virgin sand. The mechanical properties of mortar made from pulsed power sand are satisfied and relevant to be utilized in the construction industry. It was confirmed in the pulsed discharge method, that the recovered aggregate could be reduced by giving a large number of discharges, but the cement paste portion could be almost removed.

Dependence of diameter on flow velocity of liquid metal jet for repeatable pulse powered plasma sources

To realize a pulsed-power discharge plasma using a liquid metal, we investigated the dependence of the diameter on the flow velocity of a liquid metal flow consisting of a U-alloy. The plasma temperature was measured using a pyrometric method. The results show that the flow velocity estimated by the parabolic corresponds to a theoretical value derived from the difference between the gas pressure and atmospheric pressure. The diameter of the liquid metal flow was found to be 0.5 to 0.9 times smaller than the nozzle diameter. We have also demonstrated pulsed-power discharge using this liquid metal load by observing optical emission from plasma. The results indicated that a low-temperature plasma was generated by the proposed method.

Electron Behavior in Beam Diode Driven by Intense Pulsed Power Device for Warm Dense Matter State Research of Inertial Confinement Fusion

Electron behavior in beam diode gap was analyzed numerically based on the normalized value of intense pulsed power discharge device ETIGO-II as impedance controller for dense matter state research of inertial confinement fusion. After emission of electrons from the cathode surface, acceleration time, impedance, potential distribution and velocity varies with the function of different beam diode gap. To understand the time dependent behavior of electron and beam output current for different beam diode gap, 2-d electrostatic particle-in-cell (PIC) model was carried out. According to the numerical analysis, it was found that beam output current decreases with the increase of beam diode gap distance. The electron beam diode impedance was also observed increasing with the increase of diode gap. Numerical result reproduced experimental data and useful for the understanding of experimental result for dense matter state research of inertial confinement fusion.

Observation of the thermal conductivity of warm dense tungsten plasma generated by a pulsed-power discharge using laser-induced fluorescence

To observe the transport properties of a sample of warm dense matter, we used laser-induced fluorescence to measure the thermal conductivity of tungsten plasma confined within a rigid, ruby capillary tube. We determined the density and temperature of the plasma generated by an isochoric heating device using a pulsed-power discharge. The density was determined by the initial diameter of the tungsten wire used, and the temperature was obtained by spectroscopic measurements. The temperature of the ruby capillary was obtained from its fluorescence intensity, which depends on the temperature of the outer wall. We found the thermal conductivity to be approximately 30 W/K m, thus demonstrating that the thermal conductivity of warm dense matter states can be directly evaluated using the proposed method.

Input Energy Control Using Electron Beam Diode as Impedance Controller to Study Warm Dense Matter by Pulsed Power Discharge with Isochoric Heating

Input Energy Control Using Electron Beam Diode as Impedance Controller to Study Warm Dense Matter by Pulsed Power Discharge with Isochoric Heating

Accelerated ions from pulsed-power-driven fast plasma flow in perpendicular magnetic field

To understand the interaction between fast plasma flow and perpendicular magnetic field, we have investigated the behavior of a one-dimensional fast plasma flow in a perpendicular magnetic field by a laboratory-scale experiment using a pulsed-power discharge. The velocity of the plasma flow generated by a tapered cone plasma focus device is about 30 km/s, and the magnetic Reynolds number is estimated to be 8.8. After flow through the perpendicular magnetic field, the accelerated ions are measured by an ion collector. To clarify the behavior of the accelerated ions and the electromagnetic fields, numerical simulations based on an electromagnetic hybrid particle-in-cell method have been carried out. The results show that the behavior of the accelerated ions corresponds qualitatively to the experimental results. Faster ions in the plasma flow are accelerated by the induced electromagnetic fields modulated with the plasma flow.

Study on AC-DC Electrical Conductivities in Warm Dense Matter Generated by Pulsed-power Discharge with Isochoric Vessel

To observe AC and DC electrical conductivity in warm dense matter (WDM), we have demonstrated to apply the spectroscopic ellipsometry for a pulsed-power discharge with isochoric vessel. At 10 μs from the beginning of discharge, the generated parameters by using pulsed-power discharge with isochoric vessel are 0.1 ρs (ρs: solid density) of density and 4000 K of temperature, respectively. The DC electrical conductivity for above parameters is estimated to be 104 S/m. In order to measure the AC electrical conductivity, we have developed a four-detector spectroscopic ellipsometer with a multichannel spectrometer. The multichannel spectrometer, in which consists of a 16-channel photodiode array, a two-stages voltage adder, and a flat diffraction grating, has 10 MHz of the frequency response with covered visible spectrum. For applying the four-detector spectroscopic ellipsometer, we observe the each observation signal evolves the polarized behavior compared to the ratio as I1/I2.

Study on Exploding Wire Compression for Evaluating Electrical Conductivity in Warm-Dense Diamond-Like-Carbon

To improve a coupling efficiency for the fast ignition scheme of the inertial confinement fusion, fast electron behaviors as a function of an electrical conductivity are required. To evaluate the electrical conductivity for low-Z materials as a diamond-like-carbon (DLC), we have proposed a concept to investigate the properties of warm dense matter (WDM) by using pulsed-power discharges. The concept of the evaluation of DLC for WDM is a shock compression driven by an exploding wire discharge with confined by a rigid capillary. The qualitatively evaluation of the electrical conductivity for the WDM DLC requires a small electrical conductivity of the exploding wire. To analyze the electrical conductivity of exploding wire, we have demonstrated an exploding wire discharge in water for gold. The results indicated that the electrical conductivity of WDM gold for 5000 K of temperature has an insulator regime. It means that the shock compression driven by the exploding wire discharge with confined by the rigid capillary is applied for the evaluation of electrical conductivity for WDM DLC.

Numerical Simulation on Measurement of Optical and Thermal Properties for Warm Dense Matter Generated by Isochoric Heating with Pulsed Power Discharge Device

Property data in warm dense matter (WDM) are important to optimize implosion dynamics in a fuel pellet of inertial confinement fusion (ICF). A table-top pulsed power discharge device with isochoric heating using a sapphire hollow capillary was proposed, and was used to generate the extreme state of matter with a well-defined condition. We investigated numerically to generate the WDM by using the pulsed power discharge device. The numerical model was developed by time-dependent one-dimensional thermal diffusion with radiative transfer of multi-group approximation, and the numerical simulation was carried out according with the experimental condition. The achieved temperature of the numerical simulation result was confirmed by the previous experimental result. Also, the radiation energy density was shown at each group of the wavelength of emission.

An Application of Pulsed Power Technology and Subcritical Water to the Recycling of Asphalt Concrete

In order to resolve the issues related to the recycling of asphalt concrete, this study focuses on the application of pulsed power technology and subcritical water to the recovery of asphalt from asphalt concrete lumps. At the result, the recycled aggregate over 5 mm with asphalt content of approximately 0.99% was produced using pulsed power technology. Furthermore, the application of subcritical water to recover asphalt from the residues of pulsed power discharge inside of asphalt concrete lumps resulted in an about 91% pure asphalt recovery rate and recycled fine aggregate with pure asphalt content of less than 0.5%.

Nonlinear Theory Modeling Electron Beam Constriction in a Pulsed Power Discharge

A simple nonlinear theory is developed to examine the process of electron channeling and constriction for an energetic electron beam passing through a cool thermalized plasma discharge. A number of different perturbations characterize and categorize the physical process of the three-fluid system. In this model, the electron species is separated into two different species of the same type but with very different initial particle states. A normalized set of curves parameterize the conditions most probable leading to electron channeling and pinch (beam constriction) in a pulsed power glow discharge. The theory suggests that energetic secondary electron emission at the cathode is responsible for glow discharge constriction in a pulsed power discharge.

Evaluation of Transport Properties in Warm Dense Matter Generated by Pulsed-power Discharge for Nuclear Fusion Systems

Abstract To achieve the thermonuclear fusion systems, the physical properties of warm dense matter (WDM) are key parameters. In this paper, we review the evaluation of physical properties in WDM by using pulsed-power discharges. To evaluate the thermal conductivity for a divertor wall in magnetic confinement fusion, we investigate a semi-empirical evaluation based on the experimental values for electrical resistivity. The results indicate that, in the region between the interme- diate degeneracy and the non-degeneracy, the evaluated thermal conductivity has an inflection point. To evaluate the electrical resistivity for the fuel target in the inertial confinement fusion, an isochoric heating by using pulsed-power discharge in the pressure vessel has been demonstrated. The results indicate that the electrical resistivity in WDM for gold is 100 μΩ m at 0.1ρ s (ρ s : solid density) of density and the internal energy is 1MJ / kg.

Evolution of plasma loops in a semi-toroidal pinch experiment

The FlareLab experiment is a pulsed-power discharge generating magnetized plasma loops similar to a pinch experiment in a semi-toroidal configuration. After gas breakdown along a circular magnetic guide field, the structure expands in its major radius as the plasma becomes highly conductive and the discharge current rises. Photographs, current and electron density measurements reveal a significant broadening in the lateral direction leading to an increasing departure from radial symmetry of plasma parameters in the cross section. It is shown that the luminosity is related to both high electron density and high current density. Simultaneous measurements of current density and electric field reveal a high parallel resistivity of the plasma leading to fast diffusion across the magnetic field. Indications for anomalous resistivity are found by comparison with the Spitzer formula. As the experiment differs from a z-pinch experiment only by the semi-circular shape of the current path, the observed evolution is unexpected and might be of more fundamental significance.

小型高輝度短波長光源に向けたパルス発生器の設計と超音速Heガス流による液体金属流の制御法の検討

To demonstrate repetitive-intense X-ray source by using pulsed-power discharge, we proposed an innovative X-pinch method using compact pulse generator and liquid metal injection. The compact pulse generator using small pulse-forming-network modules (PFNMs) has been developed. The current rising rate of the PFNMs with X-pinch system is over 0.1 kA/ns at low operation voltage. To suppress the expansion of liquid metal in a vacuum chamber, we have demonstrated liquid metal injection with coaxial supersonic flow generated by an aerospike nozzle. The results indicate that the expansion of liquid metal is suppressed with the coaxial supersonic flow.

Reduction of contaminated concrete waste by recycling aggregate with the aid of pulsed power discharge

The Fukushima Dai-ichi Nuclear Power Plant accident has resulted in a large amount of radioactively contaminated concrete. The aim of this study is to investigate the possible application of the pulsed power discharge to reduce the amount of contaminated concrete as radioactive waste. An applicability of pulsed power discharge as a decontamination method by separating contaminated matrix from uncontaminated coarse aggregate was examined. In this study, a stable cesium (Cs) isotope was used to simulate radioactively contaminated concrete. As a result, while the volume of reclaimed aggregate from radioactive contaminated concrete reproduced by the electric pulsed discharge could reach 60%, nevertheless Cs detected in the reclaimed aggregate was only approximately 3% of quantity included in the concrete specimen. Thus most of the Cs was dissolved in water during the discharge process. It is expected that the decontamination method by the pulsed power could reduce the contaminated concrete waste by reusing aggregate. Further investigations are requested to test the applicability of this method under the realistic conditions close to the actual waste.