Plasma Kernel Research Articles

A gas dynamic perspective on particle lifting in electrostatic discharge-like devices using multiphase particle-in-cell approach

Although particle–laden electrostatic discharges are widely used in laboratories as well as in industrial applications, the mechanism of particle lifting for particles initially at rest in such highly unsteady systems is not well understood. A multiphase gas–particle solver is developed using the multiphase particle-in-cell (MP-PIC) approach to emulate the interaction of a compressible shock-dominated gas phase with the dense particle phase. First, the two-way coupled solver is initially used to study the interaction of a planar traveling shock with a vertical curtain of particulates. The gas and particle phase evolution was found to be in good agreement with a similar experimental study in Ling et al. [Phys. Fluids 24, 113301 (2012)]. Second, the MP-PIC code is used to study the interaction of an expanding blast wave with a thick bed of particles. The simulation considered forces such as quasi-steady drag, pressure-gradient, added-mass, Saffman, and Magnus forces. We observe that the vertical liftoff particles close to the shock impingement point in this configuration are associated with the quasi-steady drag, pressure gradient, and added-mass forces. Also, the Saffman lift and Magnus forces contribute to lifting particles located radially farther away from the shock impingement point. In addition, the study finds a decrease in particle lifting efficiency with decreasing plasma kernel length and shock strength.

Edge Behavior of Higher Complex-Dimensional Determinantal Point Processes

As recently proved in generality by Hedenmalm and Wennman, it is a universal behavior of complex random normal matrix models that one finds a complementary error function behavior at the boundary (also called edge) of the droplet as the matrix size increases. Such behavior is seen both in the density of the eigenvalues and the correlation kernel, where the Faddeeva plasma kernel emerges. These results are neatly expressed with the help of the outward unit normal vector on the edge. We prove that such universal behaviors transcend this class of random normal matrices, being also valid in a specific “elliptic” class of determinantal point processes defined on mathbb C^d, which are higher dimensional generalizations of the determinantal point processes describing the eigenvalues of the complex Ginibre ensemble and the complex elliptic Ginibre ensemble. These models describe a system of particles in mathbb C^d with mutual repulsion, that are confined to the origin by an external field {mathscr {V}}(z) = |z|^2 - tau {text {Re}}(z_1^2+ldots +z_d^2), where 0le tau <1. Their average density of particles converges to a uniform law on a 2d-dimensional ellipsoidal region. It is on the hyperellipsoid bounding this region that we find a complementary error function behavior and the Faddeeva plasma kernel. To the best of our knowledge, this is the first instance of the Faddeeva plasma kernel emerging in a higher dimensional model. The results provide evidence for a possible edge universality theorem for determinantal point processes on mathbb C^d.

Chasing ICM cooling and AGN feedback from the macro to the meso scales in the galaxy cluster ZwCl 235

Aims. We aim to investigate the interplay between the intracluster medium (ICM) and the active galactic nucleus (AGN) in ZwCl 235, a galaxy cluster with high X-ray flux, an extended central radio galaxy, and evidence of multiphase gas at its center. Methods. Using archival data from the Chandra telescope, the Very Large Array Sky Survey (VLASS), the LOFAR Two-metre Sky Survey (LOTSS), and the VLBA telescope, we performed a complete study of ZwCl 235, dissecting the dynamics of the ICM, the thermodynamic state of the central gas, and the properties of the brightest cluster galaxy (BCG). By means of radial profiles and 2D spectral maps, we measured the temperature, entropy, and cooling time of the ICM, and we compared the morphology of the central radio galaxy with the surrounding medium. Results. We find evidence that ZwCl 235 is a sloshing cool core cluster in which the activity of the central galaxy has excavated a pair of cavities and possibly uplifted enriched gas to an altitude of ∼30 kpc. In the cluster core, the lowest entropy ICM is preferentially found in a 20 kpc-long filament tangential to the southern radio lobe of the AGN. We argue that the observed cool (∼1.3 keV) filament is likely produced by a combination of sloshing and stimulated ICM cooling, which may be fueling the central supermassive black hole. Additionally, we determined that the X-ray emission of the BCG originates from a ∼1.4 keV plasma kernel, which extends for 5 kpc in radius and has a short cooling time (∼240 Myr), and it could represent the thermal corona of the BCG. Conclusions. Overall, we propose that several sources (the large-scale ICM, the low entropy filament, and the ∼1.4 keV kernel) of cold material are currently feeding the central AGN, and that the ICM cooling cycle expectations are met from the macro scales (between 5−100 kpc) to the meso scales (≤5 kpc) of AGN feedback.

Plasma kernel model and energy transformation characteristic of plasma synthetic jet actuator

This article conducted a theoretical, experimental, and numerical investigation to clarify the plasma kernel model and energy transformation characteristics of the plasma synthetic jet actuator (PSJA). Plasma kernel and blast wave theory were used to describe the formation and evolution of the arc-discharge energy deposition process and build a plasma kernel model. Schlieren experiment visualized the formation and evolution of the synthetic jet flow and used it as a validation of the numerical simulation. Five plasma synthetic jet actuators with different cavity volumes (128–512 mm3) and different discharge energy (2.8–11.3 mJ) were modeled numerically to investigate the energy transformation characteristic of PSJA. Results showed that plasma kernel radius and formation time could be theoretically predicted with specific deposition energy and correspond well with simulation results. The peak pressure and temperature rise in the cavity can also be calculated. Moreover, the proportion of kinetic energy increases linearly with non-dimensional deposition energy, while potential energy has a reverse tendency with non-dimensional cavity volume and deposition energy.

Numerical simulation of the evolution of shock waves and plasma kernels of multi-point laser-induced plasma in supersonic flow

Compared with single-point laser-induced plasma, multi-point laser-induced plasma shows some advantages in ignition and flameholding, but with little research. Therefore, numerical studies of multi-point laser-induced plasma in supersonic flow are conducted using an instantaneous energy deposition model. In the studies, the single-pulse laser energy of every laser focus is 50 mJ, the laser focus configuration is linear, the inflow velocities are from Ma 1.5 to Ma 2.5, and the distances between adjacent focal spots are from 2 to 4 mm. The evolution process of shock waves and plasma kernels in supersonic flow has been described in detail when the inflow velocity is Ma 2 and when the distance between adjacent focal spots is 2 mm. Besides, the evolution law of the velocity field, the streamline, and the plasma kernel position in the flow field have also been analyzed. The results reveal that the volume of the plasma kernel increases rapidly within 15 µs and that the initial shock wave has a strong deflection effect on the supersonic flow. Moreover, the effects of inflow velocities and distances between adjacent focal spots on multi-point laser-induced plasma are compared using the plasma kernel’s average temperature, volume, and specific surface area. Under the conditions of the studies, the results show that the distance between adjacent focal spots is the main reason affecting the evolution. Thus, a distance longer than 4 mm between adjacent focal spots should be avoided for multi-point laser-induced plasma in supersonic flow because the plasma kernel could not be fused in a timely manner.

Effects of non-collimated radiation during the decay of laser-induced spark

A fast-computing radiative heat transfer on-the-fly interpolation database was developed for high temperature radiative-gas dynamic simulations under local thermodynamic equilibrium (LTE). The absorption coefficient includes Atomic (Bound-Bound, Bound-Free, Free-Free) transitions and Molecular band systems. A 2D finite-volume radiative transfer equation (RTE) solver was developed and coupled with a compressible reacting flow solver to simulate a laser-induced decaying spark (LIDS) in air. Part spectrum correlated k-distribution with Gauss-Chebyshev quadrature and mixing model were applied to reduce the number of RTE runs. Non-collimated radiative heat loss was calculated in LIDS and the effects of radiation loss on the shock wave and kernel cooling were investigated. Total radiation loss was accounted to be approximately 2.3% of the absorbed energy which happens in a micro-second timescale and most of the kernel energy is taken away by the shock wave. Two simulations with and without RTE were compared to analyse the effects of radiative transfer. The radiation loss results in attenuation of shock wave velocity and delaying the emanation of blast wave. The cooling of the plasma kernel is accelerated due to energy loss by radiative transfer. Radiation increases the cooling rates in the primary cooling regime and decreases during the secondary regime due to an energy deficit in the kernel. The transition from primary to the secondary cooling regime is not uniform throughout the kernel.

Non-equilibrium plasma generation via nano-second multi-mode laser pulses

The formation and growth of plasma kernels generated via nano-second mode-beating laser pulses is investigated here via a non-equilibrium self-consistent computational model. Chemically reactive Navier–Stokes equations are used to describe the hydrodynamics, and non-equilibrium effects are taken into account with a two-temperature model. Inverse Bremsstrahlung and multiphoton ionization are included self-consistently in the model via a coupled solution of the plasma governing equations and the radiative transfer equation (that describes the laser beam propagation and attenuation). A self-consistent approach (despite carrying additional challenges) minimizes the empiricism and it allows for a more accurate description since it prevents both the utilization of artificial plasma seeds to trigger the breakdown and the implementation of tuning parameters to simulate the laser-energy deposition. The advantages of this approach are confirmed by the good agreement between the numerically predicted and the experimentally measured plasma boundary evolution and absorbed energy. This also holds true for the periodic plasma kernel structures that, as suggested by the experiments and confirmed by the simulations presented here, are connected to the modulating frequency.

Blind-zone formation in laser shockwave nano-cleaning.

Laser shockwave cleaning (LSC) has attracted growing attention due to its advantages in non-contact, site-selective nanoparticle removal on microelectronic/optical devices. However, an uncleaned blind-zone formed directly under the laser-induced plasma kernel severely affects the cleaning effect. Laser shockwave cleaning of 300 nm polystyrene latex nanoparticles on silicon wafers is fully explored to understand the blind-zone formation mechanism. The size of the uncleaned blind-zone quickly increases from 0.84 to 19.50 mm2 associated with a growing fraction of the uncleaned blind-zone area within the whole cleaned area from 0.05 to 0.93 as the plasma-substrate gap distance is increased from 0.5 to 2 mm and the laser fluence is increased from 75 to 150 J/cm2. Besides, the variation of the blind-zone size is more strongly dependent on the plasma-substrate gap distance than the laser fluence. A time-resolved analysis of the laser-induced plasma evolution shows an inseparable relationship between the blind-zone and the geometric location of the plasma kernel. Theoretical analysis of the removal force in LSC based on the rolling mode reveals that the lack of dragging force acting on the nanoparticles in the region right under the plasma kernel impedes their removal and causes the uncleaned blind-zone formation.

Computational study of a novel microwave excited plasma sensor for aerodynamic flows

We present a computational study that demonstrates the concept of a microwave excited plasma flow sensor. The geometric configuration consists of an array of circularly arranged “receiver” (ground) electrodes that surround a central “transmitter” (excited) electrode that is flush mounted on a surface exposed to incident flow. Microwave excitation is used to strike a low-temperature plasma between the transmitter electrode and the receiver electrode. Depending on the flow direction, a more intense plasma kernel is formed between the transmitter electrode and the downstream electrode for sufficiently strong excitation conditions. The differential current between the receiver electrodes is used to establish the flow direction and magnitude. The computational model establishes the effectiveness of the concept as a flow sensor. Parametric studies involving excitation voltages, flow velocities, scale lengths, electrode shape, and excitation frequency are performed. It is observed that the sensitivity of the device to the imposed flow is considerably improved with increasing excitation frequency in the microwave regime.

Study of particle lifting mechanisms in an electrostatic discharge plasma

Although particle-laden electrostatic discharges are widely used in research as well as in industrial applications, the mechanisms of particle lifting for a particle initially at rest in such highly unsteady flows are not well understood. A multiphase plasma flow is modeled by solving the continuum conservation equations and particles as discrete entities in a Lagrangian approach. The gas phase solver is used to study the generation of shock waves and the high temperature plasma kernel. A one-way coupling approach between the two phases is used and various Lagrangian sub-models are developed to study the particle phase evolution in the system. Comparison with shock tube measurements where a planar shock wave perpendicular to the shock tube wall interacts with particles residing on the wall showed that the predominant mechanism of particle lifting is the Saffman force generated on particles due to velocity gradients in the gas boundary layer. A second configuration with an overhead spherical blast wave generated by an electrostatic discharge (ESD) interacting with a polydisperse distribution of spherical particles placed at three wall-electrode distances was considered. The predicted particle lifting heights and velocities are found to compare well with measurements in an ESD configuration initiated by the dielectric breakdown of ambient air.

Ignition of zirconium powders placed near an electrostatic discharge

Abstract Electrostatic discharge (ESD) or spark produced by breakdown of a gap while discharging a capacitor is a common ignition stimulus for powders of reactive and energetic materials. It is a safety hazard, but is also used to initiate pyrotechnic formulations and as a characterization method of reactivity of energetic materials. In previous experimental studies, the powder served as one of the ESD electrodes. Ignition was found to be caused by Joule heating, with the main heat release by current passing through points of contact between particles. However, ignition may occur when the ESD does not pass directly through the powder. ESD generates a shock wave, which can lift the powder from a substrate even if the substrate is not an electrode. ESD also generates a plasma kernel heated to ca. 10,000 K, which exists for hundreds of µs, often much longer than the ESD current. Here, the effect of the ESD-induced shock and plasma on a reactive powder was studied experimentally for the first time. A thin layer of Zr powder was placed on a substrate located under a spark gap between two pin electrodes. Photo-sensors and high-speed video were used to document ignition and combustion events. The ESD energy and distance from the spark gap and powder were varied. At close distances, particles ignited consistently. Distance limits were determined, beyond which ignition was no longer observed. Higher ESD energies as well as longer ESD pulses led to ignition at greater distances. Ignition involved two distinct processes. First, submicron particles were lifted from the substrate on a time scale of single microseconds, interacted directly with the plasma kernel, and combusted. Optical emissions from this combustion lasted 100 – 600 µs, as expected for the burn time of submicron Zr particles in air. The second ignition event occurred several milliseconds later. It involved a flame propagating through Zr powder aerosol or combustion of individual lifted particles. This event was caused by coarser Zr particles radiatively heated during ESD. Importantly, the powder was aerosolized by convective flows caused by the rising plasma kernel making it possible for the self-heating of particles oxidizing in air to eventually lead to their ignition and combustion. Observed times for these delayed ignition and combustion events were in the order of tens of milliseconds.

Modeling of plasma combustion ignition on an electromagnetic wave driven metasurface

We present a multi-physics model of combustion ignition phenomena in an atmospheric pressure hydrogen-air mixture ignited by a microwave surface plasma discharge. The surface plasma is generated over a resonant metasurface structure that provides sufficient field intensification to break down and sustain a discharge. Specifically, a surface electromagnetic (EM) wave mode known as the spoof surface plasmon polariton (SSPP) is excited to yield a hybrid resonance that results from coupling of cavity and surface EM wave modes. Motivated by the need for a large, volumetric ignition kernel for applications in combustion ignition, we numerically demonstrate the volumetric surface plasma discharge enabled by the use of this particular EM wave mode in a high pressure operating regime. We discuss the transient evolution of a centimeter scale plasma kernel and subsequent ignition kernel formation. High density combustion enhancing radical species (O, H, OH) are produced throughout the bulk plasma, which leads to successful ignition. A parametric study shows that the large size of a plasma kernel is attributed to the shortening of ignition delay.

Hydrodynamic Ejections by Dual-Pulse Laser-Induced Breakdowns

A focused laser can cause optical breakdown of a gas, forming a plasma kernel that expands rapidly and, under certain conditions, ejects hot gas along the laser axis to distances several times the kernel size. Whether this ejection occurs and its intensity and direction depend on the breakdown parameters and can affect subsequent flame growth in combustible mixtures. One approach to alter, and potentially control, the character of this ejection is a dual-pulse configuration. Detailed simulations are used to study the post-breakdown hydrodynamics in an inert gas, which reproduce key experimental observations. In the first configuration analyzed, a weak pulse disrupts vorticity generation by a stronger pulse, suppressing the ejection that would have been produced by the stronger one alone. In a second configuration, we show that adjusting temporal and spatial separation can access a broader range of phenomenologies in which the ejections can be suppressed, enhanced, or even reversed.

Collinear dual-pulse laser optical breakdown and energy deposition

A non-equilibrium model for laser-generated plasmas is used to represent collinear dual nano-second-pulse interactions. In the specific case considered, the breakdown is initiated with an ultraviolet (UV) laser pulse at 266 nm, which pre-ionizes the gas, and it is followed by a near-infrared (NIR) pulse at 1064 nm, which deposits significant energy into the ionized mixture. The model is validated against corresponding experiments, and simulation results are interrogated to understand key features of the plasma-kernel dynamics and the post-discharge hydrodynamics. The hydrodynamics of the non-equilibrium plasma is governed by the two-temperature Navier–Stokes equations accounting for both multiphoton ionization and inverse bremsstrahlung. The interaction between the laser beam and the plasma is modeled based on the radiative transfer equation. The temporal and spatial offsets of the two pulses can generate ionization kernels with different topology and dynamics. It is shown that the UV pre-ionization pulse can tailor the plasma region, leading to a larger ionized volume than would occur for a single-pulse breakdown, and it increases the efficiency of the energy deposition for the following NIR discharge. Vorticity in the early post-discharge phase is generated via baroclinic torque from the misalignment of the radial gradient of density (sudden gas expansion) and the strong pressure gradient (initiated by energy deposition from the laser beam). It is predicted that the collinear dual pulse can be designed to specify the plasma kernel size, shape, and maximum temperature in the breakdown phase, and the initial post-breakdown vorticity and plasma-core decay.

Experimental and numerical investigations of double pulse laser energy deposition in air

This study focuses on the laser energy deposition characteristics through single and double pulse at short and long pulse intervals in quiescent air, both experimentally and numerically. A frequency-doubled and Q-switched Nd: YAG laser is used to create the spark in the air. High-speed schlieren imaging technique is used to visualize the shock-wave evolution and plasma kernel expansion. To estimate the energy available for ignition, the energy absorbed is measured and the energy loss through the shock-wave is estimated by using Jones blast wave model. Two-dimensional numerical simulations are carried out by solving the Navier-Stokes equations along with the species conservation equations in finite volume framework. After cessation of the laser pulse, the breakdown zone assumed to consists of seven species (O2, O, N2, N, NO, NO+ and e−). For double pulse at short pulse interval, the second pulse absorbed more energy than the first pulse, and the shock loss is relatively higher. The lifetime of plasma is found to have increased by 13.56 % due to the jump in temperature and pressure after the introduction of the second pulse. Same total energy two successive laser pulses at short time interval are found to be a promising alternative of single pulse for lean limit of combustion. The amount of energy left in the kernel for ignition is 16.02 % and 15.78 % of the absorbed energy in 50 + 50 mJ and 100 + 100 mJ double pulse respectively. In case of double laser pulse deposition at long pulse interval, along with multiple layers of shock-wave, a third lobe and a fourth lobe are observed on either side (upstream and downstream) of the plasma kernel enhancing the kernel surface area and mixing process.

Hydrodynamic ejection caused by laser-induced optical breakdown

A focused laser can cause local optical breakdown of a gas, which leads to rapid deposition of energy into a high-temperature plasma kernel that expands and induces a complex flow. For some conditions, hot gas is rapidly ejected along the laser axis up to distances several times the kernel size, with a particularly curious feature: relatively small changes in, for example, initial pressure can cause the direction of this ejection to reverse. Detailed axisymmetric simulations of a model energy kernel in an inert gas provide a hydrodynamic description of this phenomenon, reproducing key observations in corresponding experiments, including the vortex-ring-like features that constitute the ejection. These simulations are analysed to show how changes in the early-time kernel can lead to ejection or its reversal via alteration in the relative strength and position of the vorticity produced. A corresponding semi-infinite geometry is used to isolate two mechanisms: vorticity production by the generated shock and by baroclinic torque at the kernel boundary. Dependence on the initial kernel asymmetry is quantified, as it ultimately determines whether the vorticity, upon its subsequent evolution, develops into the ring-like structure that ejects. Even simple elongation of the energy kernel alone can reverse the direction.

Laser-induced non-equilibrium plasma kernel dynamics

A non-equilibrium model for laser generated plasmas is validated and used to investigate plasma kernel dynamics. Breakdowns in quiescent air at different ambient conditions (e.g. pressure) for different laser parameters (e.g. power density and beam wavelength) are considered. The hydrodynamics is described based on the chemically reactive Navier–Stokes equations where non-equilibrium effects are accounted for using a three-temperature model. Laser-plasma interactions over nano-second time-scales are modeled with a radiative transfer equation (RTE), including both multiphoton ionization (MPI) and inverse Bremsstrahlung (IB). Validation is conducted by comparing absorbed energy and plasma emission with the corresponding experimental measurements, and by observations of the structure of the breakdown. The laser generated plasma exhibits a two-lobe structure, developing both in the forward and backward directions. An analysis of the dynamics suggests that the kernel evolution results from a radiation-driven wave that is: (i) triggered by MPI, (ii) sustained by energy deposition in IB interactions, which compensates for the energy lost by free-electrons in ionizing collisions, and (iii) guided by both MPI and ionization by electron impact (IE).

Temporally and Spatially Resolved Emission Spectroscopy of Hydrogen, Cyanide and Carbon in Laser-Induced Plasma

In this study, we examine the atomic and molecular signatures in laser-induced plasma. Abel inversions of measured line-of-sight data reveal insight into the radial plasma distribution. Laser-plasma is generated with 6 ns, Q-switched Nd:YAG radiation with energies in the range of 100 to 800 mJ. Temporally- and spatially-resolved emission spectroscopy investigates expansion dynamics. Specific interests include atomic hydrogen (H) and cyanide (CN). Atomic hydrogen spectra indicate axisymmetric shell structures and isentropic expansion of the plasma kernel. The recombination radiation of CN emanates within the first 100 nanoseconds for laser-induced breakdown in a 1:1 mole ratio CO2:N2 gas mixture. CN excitation temperatures are determined from fitting recorded and computed spectra. Chemical equilibrium mole fractions of CN are computed for air and the CO2:N2 gas mixture. Measurements utilize a 0.64-m Czerny–Turner type spectrometer and an intensified charge-coupled device.

Hydrodynamic regimes induced by nanosecond pulsed discharges in air: mechanism of vorticity generation

The mechanisms controlling the hydrodynamic effects induced by nanosecond pulsed discharges applied between two pin electrodes in air at atmospheric conditions are investigated experimentally and numerically. A cylindrical plasma kernel is formed between the electrodes during the discharge. After the discharge, schlieren images show that the cylindrical kernel evolves in different ways depending on the gap distance: (1) for short gap distances (), the cylindrical kernel collapses to form a torus-like structure. In this case, the flow field presents a significant source of vorticity; (2) for larger gaps (), the kernel retains its initial cylindrical shape and cools down primarily through heat diffusion. The objective of this work is to understand the mechanisms leading to the formation of these two hydrodynamic regimes. To this end, simulations were performed and compared with the experimental schlieren images. It is shown that the main source of vorticity is the baroclinic torque caused by the cylindrical blast wave that follows the fast energy addition during the discharge. Finally, a criterion is given to predict the occurrence of the two hydrodynamic regimes. This criterion is then validated against experimental results from the literature.

Spatial evolution of the plasma kernel produced by nanosecond discharges in air

This work presents an experimental investigation of the hydrodynamic effects induced by nanosecond and conventional spark discharges. The energy deposited in sparks in the short breakdown time (~1 mJ mm−1) induces hydrodynamic effects that redistribute the energy over a large volume (~1 cm3) surrounding the initial plasma channel. This process influences the subsequent formation of the ignition kernel and the initiation of combustion. The experimental results presented in this paper were obtained with a set of synchronized diagnostics including schlieren, OH planar laser induced fluorescence and electrical measurements of the energy deposited in the plasma. It is shown that the motion of the gas excited after the discharge breakdown depends not only on the total deposited energy but also on the dynamics of the energy input in the plasma. Finally, the effects of nanosecond sparks are compared with those of conventional sparks used for internal combustion engines. We show that, with 20 times less energy, the nanosecond spark produces a twice bigger excited gas volume than the conventional spark. This is because the energy deposited by the nanosecond spark during the breakdown stage is three times higher than for the conventional spark.