Electric field measurement has a wide range of applications in high voltage field. Most of the traditional electric field measurement methods belong to interventional measurement category, which will cause distortion to the measured electric field. The electric field measurement method based on the electricfield-induced second harmonic (EFISH) effect has the advantages of non-intrusive and high spatial and temporal resolution [1–3]. However, to simulate the spatial synthetic electric field under the actual transmission line during corona discharge, the method of electric field calibration under the wire-plate electrode structure and the measurement of the electric field under the wire under the corona state are not clear.
Terahertz (THz) biological detection and sensing play a vital role in people well-being, with a focus on achieving efficient biological effects and convenient integration of biosensing and fingerprint spectrum recognition [1–5] . However, current efforts often confine sensing to traditional transmission or reflection metasurface observations, and continuous fingerprint spectrum recognition typically relies on a continuous tuning unit array corresponding to individual frequency points. This approach significantly limits sensitivity improvement and exacerbates the design and integration constraints of components. In this study, leveraging the sensing potential of the long-range propagation characteristics of surface waves excited by metasurfaces, we employ the continuous collection and accumulation of dielectric environment information during the extended transmission of surface waves on component surfaces. Consequently, we achieve high-sensitivity refractive index sensing, reaching up to 215.5°/RIU, and continuous fingerprint spectrum recognition in an integrated untuned structure, which is realized by considering both the surface wave transmission phase and amplitude. Our approach introduces a novel strategy for enhancing metasurface sensitivity, sidestepping integration limitations associated with continuous tuning units, and facilitating the efficient integration of multiple sensing properties.
The dielectric surface contacting to vacuum is the weakest part of the vacuum insulation system widely used in pulsed power applications due to surface flashover phenomenon. A large number of researches have been conducted on vacuum surface flashover under many kinds of conditions such as DC voltage, microsecond pulse, except multi-pulse voltage. The experiment platform in Institute of Fluid Physics could generate square wave triple-pulse at MHz repetition by converging three outputs from Marx-Blumlein pulse forming lines in parallel. We have studied the difference of vacuum surface flashover voltages of the first and subsequent pulses on aforementioned platform. The formation of penetrating flashover channel was observed, which is significant to understanding the complex process of surface flashover.
Fusarium graminearum (F. graminearum), a pathogenic fungus, induces Fusarium head blight (FHB) in wheat, leading to reduced yields and economic losses. More severely, F. graminearum can produce various mycotoxins on contaminated grains, posing a significant threat to human and livestock health. Recently, plasma-activated water (PAW) has shown promising applications in the microbial inactivation due to its low cost, easy operation, high efficiency, eco-friendliness, and without toxic byproducts. However, the current reports on the impact of PAW on the growth of plant-pathogenic fungi, the biosynthesis of fungal mycotoxins, and its field efficacy in preventing plant fungal diseases remain limited.
In order to study the species and density of metastable and excited particles after gas switch discharge, a broadband absorption spectrum source based on Z-pinch plasma is developed. This source consists of a pulse power circuit which generates a pulse current of more than 60 kA and a cylindrical quartz tube where the pulse current drives the gas Z-pinch discharge. At the stagnation time, high temperature and high density plasma is generated on the axis of the cylindrical discharge tube resulting in a intense band board radiation spectrum. In order to study the radiation characteristics of intense and continuous radiation spectrum produced by Z-pinch plasma under different parameters, the axial radiation spectrum at stagnation time is measured with varying driving current and gas parameters (pressure and types). By analyzing these measurements, the optimum parameters are determined to improve the intensity and spectral range of the broadband absorption spectrum source.
Underwater electrical wire explosion (UEWE) was accompanied with rich physical phenomena such as shock waves, radiation, and strongly coupled plasmas, offering valuable applications in high energy density physics research. Over the past few decades, the uniformity of discharge channels in UEWE has been widely studied. Non-uniform discharge channels may affect the measurements of thermodynamic states and electrical conductivity, and can also disrupt the symmetry of converging shock waves in underwater electrical explosion of wire array. Axially non-uniform discharge channels have been observed by different researchers under various conditions, but the mechanisms behind their formation remain inconclusive. Here, we performed multiscale simulations to understand the formation of non-uniform discharge channels in UEWE. Thermodynamic evolution of exploding wires driven by different pulsed power supply were computed based on a magneto-hydrodynamic model. The results indicated that electrothermal instability would increase rapidly when the exploding wire transferred into a liquid-vapor coexistence state, resulting in a bamboo-like discharge channel. Combining perturbation theory, the growth of electrothermal instability is attributed to the decrease in electrical conductivity with density during the phase transition process. Furthermore, molecular dynamics simulations were conducted to analyze the phase transition dynamics during UEWE, and foam-like structures was observed in the liquid-vapor coexistence state. Significant density fluctuations may serve as the root cause of the rapid growth of electrothermal instability. Increasing the energy deposition rate allows exploding wires to undergo the liquid-gas transition through a supercritical state instead of the liquid-vapor coexistence state, thereby suppressing the growth of electrothermal instability, which agreed with previous experimental results.
Lightning strikes on aircraft are mainly due to bidirectional leader discharge triggered by the aircraft itself, which provides an important basis for the proper assessment of the electromagnetic threat and the development of design standards for aircraft lightning protection. In this paper, an observation platform of long air gaps containing a floating conductor with a configuration of the plate-rod-plate gap was established. The discharge observation tests of air gaps with the floating conductor under a negative background electric field were carried out. The data of the discharge morphology, the leader luminosity, and the leader extension speed were obtained to study the discharge development process. The experimental results show that the rod-shaped floating conductor discharge presents bipolarity; the discharge development at the negative end of the floating conductor lags behind that at the positive end; the characteristic phases of the development of the positive discharges (corona burst, re-illumination and an increase in the velocity) are related to changes in the conditions of propagation of the discharge at the opposite end of the floating electrode (formation of coronas, initiation of leaders). This study can provide a theoretical basis for modeling long air-gap discharges containing a floating conductor, which is of great significance in improving the understanding of the physical processes of lightning strikes on aircraft.
This investigation delves into the dynamics governing the transport of high-energy negative ion beams within plasma targets, employing a 2D3V Particle-in-Cell (PIC) model coupled with Monte Carlo (MC) collision simulations. The simulation shows the pulse modulation process of ion beam and plasma, unveiling short-pulse formations influenced by plasma density and beam energy. In low ionization density plasma targets, the principal neutralization processes unfold through intricate collisional reactions, giving rise to an equilibrium curve of neutralization efficiency characterized by an initial ascent followed by a subsequent decline. The simulation outcomes seamlessly align with theoretical calculations, thereby substantiating the model’s precision in the context of neutral gas targets. In high ionization density plasma targets, an augmentation in the ionization degree demonstrably amplifies neutralization efficiency while concurrently diminishing the optimal gas target thickness. The study meticulously elucidates the nuanced roles of pivotal reactions, including electron detachment, reionization and charge exchange, in sculpting the curves of neutralization efficiency. Experimental validation conducted at 10% ionization density substantiates the accuracy of the simulations. These findings not only enrich the theoretical underpinnings for the optimization of Neutral Beam Injection (NBI) systems but also underscore the intricate interplay between ion beam transport dynamics and plasma interactions.
In the ion extraction process, the spatiotemporal distributions of the electric fields under different electrode configurations may have a significant influence on the charged particle transport characteristics. In this study, with the existing □-type and M-type plate configurations as examples, the spatiotemporal distributions of the electric fields, the number fluxes of the charged particles to the electrodes, as well as the corresponding collection area on the electrodes, are studied based on the particle-in-cell (PIC) simulations. This research not only deepens the understandings to the mechanisms of non-equilibrium charged particle transports, but also provides new ideas for designing novel electrode configurations to improve the number fluxes of the extracted charged particles in bounded decaying plasmas.
When Thio [1] attempted the first design of a spherical configuration of 60 plasma guns for PJMIF in 1997, he adopted the geometry of the bucky ball emulating the ICF facility OMEGA at LLE of the University of Rochester. The geometry is used for the PLX experiment at Los Alamos National Laboratory [2].
Ion beam transport processes in plasmas are of great importance to many areas of modern physics. Experimental and simulation studies of ion beam transport in plasma are of great significance to the development of related disciplines.
The environmentally friendly switchgear that employs dry air as an insulating medium has extensive application prospects. Monitoring the decomposition components of partial discharge in dry air is of paramount significance for assessing defects in this type of switchgear. This study utilizes Gaussian simulation software to analyze potential pathways for partial discharge decomposition in dry air, calculating the reaction heat for various chemical reaction pathways. The proposal is to employ the decomposition gases CO 2 , CO, and NO 2 as characteristic components to reflect the types of defects in dry air-insulated switchgear. Various experimental platforms were established to study the distribution patterns of decomposition components of dry air under different discharge voltages and times for different defect types, including metal protrusions, insulator gap defects, and insulator metal contamination defects. The research indicates that with increasing discharge time and voltage, the concentrations of decomposition gases CO 2 , CO, and NO 2 linearly increase, with NO 2 gas concentration reaching saturation first. The selection of c(CO 2 +CO)/c(NO 2 ) and c(CO 2 )/c(CO) as characteristic quantities is proposed to discriminate the types of partial discharge defects in dry air-insulated switchgear. This serves as a reference basis for the monitoring and diagnosis of defect types in dry air-insulated switchgear.
Along with the rapid development of pulsed power technology, surface flashover along insulators has become a key bottleneck in restraining the improvement of power, reliability and compact structure. Consequently, exploring the mechanism of insulation failure can contribute to accelerating the iteration of cutting-edge insulating craftwork, which is of great significance for elevating the electrical resistance of insulators. In this work, one novel insulator consisting of compacted multilayer polyimide films is designed and manufactured. Besides, an integrated optical-electrical diagnostic platform is constructed to obtain the key parameter determining the insulating characteristics. Profiting from the dense stacked structure, the tested insulator showed excellent ability to withstand pulse voltage, which is about two times compared with the same kind of integrated block structure insulator. Additionally, the overall flashover voltage can be significantly increased by reducing the thickness of the monolayer film. Based on the synthetic measurement, local charge accumulation is suppressed and the surface breakdown process is impeded. The experiment revels that such multilayer structure can cause a great reduction in the space electric field, which further inhibits secondary electron emission and surface breakdown.
The outermost layer of human skin, known as the stratum corneum, serves as the primary barrier to protect our bodies. Within this layer, the stratum corneum lipid bilayer functions as a sophisticated biosensor, regulating metabolic activity in response to external stimuli. Electroporation, a technique widely used to enhance transdermal drug delivery, increases permeability by creating hydrophilic pores, allowing small hydrophile drugs to transport the lipid bilayer that is normally impermeable. Terahertz electroporation, characterized by longer duration and smaller sizes compared to gigahertz pulse, has been less explored in connection with transdermal drug delivery processes. This study examines the impact of monopole terahertz electroporation on stratum corneum lipid bilayer and its key components Cer2(NS), lignoceric acid, and cholesterol with four systems, which include their separated systems and a mixed system of normal stratum corneum lipid molar ratio with Cer2: lignoceric acid: cholesterol=1:1:1. In this article, we calculated a constant electric pulse in the range of 0.4-0.7 V/nm and a monopolar 0.1 THz electric pulse in the range of 0.7-1.1 V/nm, indicating the threshold voltage for the stratum corneum lipid bilayer is normally higher than the cell membrane. The infrared absorption spectra of these systems before and after electroporation were also presented to investigate the structural changes caused by electroporation. The findings contribute to a better understanding of the effects of terahertz electroporation on the stratum corneum lipid bilayer and provide valuable insights for selecting this method for transdermal drug delivery processes.
In radio frequency (RF) capacitively coupled plasma (CCP) systems, the blocking capacitor is essential because it literally blocks the direct current (DC) component from the RF power supply ensuring that only the alternating current (AC) is applied to the plasma. It prevents the accumulation of DC bias and also protects the RF power supply by blocking the DC components from plasma chamber. Using the blocking capacitor inevitably leads to the self-bias effect due to the difference in mobility between electrons and ions. The higher mobility of electrons than ions results in the imbalance of charge distribution in plasma sheath near the electrodes. This charge imbalance forms the negative DC voltage bias across the plasma sheath and controls the ion flux and the ion energy through the negative DC self-bias voltage. In this study, we discuss how the self-bias from different waveforms affects plasma characteristics in low pressure (20 mTorr) RF CCP systems using a two-dimensional particle-in-cell Monte Carlo collision (PIC-MCC) simulation. The RF sources are bipolar and unipolar dual frequency (40 MHz and 400 KHz) pulses. Also, we investigate the effect of split electrodes on the DC bias
In the process of lightning strikes on wind turbine blades, the rotational displacement modifies the charge distribution in the corona discharge area at the blade tip, setting it apart from the stationary target. Currently, micro-mechanism studies are limited, and most tests on wind speed’s impact on corona discharge under thundercloud background electric field are conducted at low flow speeds, which are insufficient for the operating environment of high-capacity turbines with high wind speed.
Z-pinch plays an important role in the field of high energy density physics such as inertial confinement fusion and radiation physics. The dynamics behavior of the Z pinch plasma and its control methods are research hotspots and trends in this field. This paper mainly summarizes the main progress achieved at Xi’an Jiaotong University in the past ten years. Diagnostics including the X-pinch backlighting, optical Thomson scattering, Zeeman-splitting spectroscopy, and Faraday rotation measure have been establishment in the 400 kA, 300 ns Qin-1 facility. The parameters of the flow velocity, electron temperature, magnetic field of the plasma were measured with spatial-temporal resolutions. Measurements of the ablation plasma confirmed the present of a resistive layer near the wire core, where the plasma underwent rapid heating. The end-on laser probing indicated the formation of the precusor plasma from the liner. Then the regulation methods of the Z-pinch plasma including the preheating by the prepulse current along with the stabilizing by axial magnetic field were investigated. With the help of the prepulse current, the ablation, precusor plasma and the tailing mass could be completely suppressing, and the development of the Magneto-Rayleigh-Taylor instabilities was further reduced by the axial magnetic field. Meanwhile, pulsed power technology based on the fast linear transformer driver (FLTD) have been developed. The FLTD brick achieved a peak power of 5.8 GW, and then the one-stage, four-stage and twelve-stage FLTD machines have be built. The twelve-stage FLTD had a current of 1.0 MA, a voltage of 1.1 MV, which could be the prototype of the next generation Z pinch facility.
Vacuum breakdown issue is one of the most important factors that restrict the performance and threat the operation of vacuum devices and equipment, like vacuum interrupters, fusion reactors, particle accelerators, and etc. While the intense electric field is applied to the metal electrode surface in vacuum environment, it is a common sense that field electron emission and the subsequent breakdown would take place over a period of operation time. However, the interaction between the high electric field and metal materials as well as the triggering mechanism of field emission and breakdown are still drawing much attention in vacuum community, in particular, how the imposed high electric field affects the metal electrodes at microscale. This work presents the state-of-the-art study on the morphology evolution dynamics of metal nanotips across nanogaps under high electric field. By utilizing an in-situ TEM electrical measurement system, we are able to record the field-induced diffusion of surface atoms and then the formation of nano-protrusions, as well as the temporal change of the nanotip contour from round shape to trapezoid shape due to the field-induced diffusion and evaporation of surface atoms. Furthermore, we summarize the relationship between field emission behaviors and the morphology evolution, and for the first time, propose the experimental evidence for the origin of field emitters generated under a high electric field. This work would greatly contribute to in-depth understanding of vacuum breakdown mechanism in accelerator applications and high energy physics.
Nuclear fusion energy is the most ideal clean energy source. Currently, there are two mainstream solutions for achieving controlled nuclear fusion internationally, laser confinement fusion and magnetic confinement fusion. During the operation of controlled nuclear fusion devices, electromagnetic pulses(EMP) are generated through various physical mechanisms. Based on the different mechanisms of electromagnetic pulse generation, our team systematically classified the electromagnetic pulses generated by controlled nuclear fusion devices in China.
The positive leader discharge is a thermal plasma characterized by low ionization and high conductivity, which occurs during the breakdown of external insulation in power apparatus and lightning discharges [1–2]. Due to the gas temperature ranging from approximately 2000K to 8000K, the positive leader exhibits in a non-local thermodynamic equilibrium (non-LTE) state [3]. Investigating the optical emission spectrum (OES) of positive leaders is crucial for understanding their kinetic mechanism under non-LTE conditions [4]. However, there is limited documentation on the OES characteristics of positive leaders in published literature [5]. This paper presents a preliminary investigation into the OES characteristics of positive leaders initiated in a 1.0 m rod-plate air gap, including spectral lines generated by excited N2, O2, O, and N during various stages such as streamer stem formation, dark period, and unstable leader phase. It is found that similar excited species can be observed during the formation of streamer stem and dark period, including the SPS (second positive bands) of nitrogen molecules (300-430nm), the FPS (first positive bands) of nitrogen molecules (741-763nm), the oxygen atom OI(1D, 715nm) and the nitrogen atom NI(4P, 674nm). Despite the FPS and SPS of N2, excited states of atoms such as OI, NI, OII and NII are recorded for the unstable leader phase. The related discharge dynamics of the main species were discussed based on observed characteristic spectral lines, which helps to improve the numerical models for both laboratory long air gap discharges and natural lightning.
