Distribution Of Plasma Parameters Research Articles

Height-modulating horizontal transport of dust particles in a dusty plasma ratchet

Dust particles are often electrostatically trapped and levitated within the non-electroneutral region of a sheath. The fascinating transport phenomena of dust particles strongly depend on the plasma parameters surrounding them within the sheath, whereas, that are quite difficult to obtain, leading to an unclear understanding of particle transport mechanisms. Here, we demonstrate a tunable horizontal transport of micron-sized dust particles by precisely manipulating their vertically suspended heights in an asymmetric ratchet sheath by designing dusty plasma ratchet. A collection of dust particles serves as micro-probes to detect the height-dependent transport properties and the feature of the sheath. Two methods are employed to lift or reduce the suspended heights of dust particles while maintaining the sheath unchanged. As the suspended heights of dust particles vary, their directional transport changes accordingly, including a flow reversal. A two-dimensional model of the ratchet sheath depicts the nonlinear distributions of plasma parameters and reveals that these unexpected transport phenomena can be attributed to the dependence of the electric ratchet potential and the resulting non-equilibrium net ion drag force on the suspended heights of dust particles. Our combined experimental and theoretical study provides insights into the fundamental transport properties of dust particles in an asymmetrical sheath.

A Novel Ionospheric Inversion Model: PINN‐SAMI3 (Physics Informed Neural Network Based on SAMI3)

AbstractPurely data‐driven ionospheric modeling fails to adequately obey fundamental physical laws. To overcome this shortcoming, we propose a novel ionospheric inversion model, Physics‐Informed Neural Network based on fully physical models SAMI3 (PINN‐SAMI3). The model incorporates the governing equations of the ionospheric physical model SAMI3 into the neural network to reconstruct the temporal‐spatial distribution of ionospheric plasma parameters. The objective of this study is to investigate the feasibility of integrating physical models with machine learning for ionospheric modeling. The PINN‐SAMI3 framework enforces physical laws through the multiple ion species of continuity, momentum, temperature equations in the magnetic dipole coordinate system. The simulation results show that if sparse ion densities are used as training data, it is possible to retrieve ionospheric electron densities, ion velocities and ion temperatures, respectively. The optimal physical constraints have been also investigated for different inversion quantities. Furthermore, the impact of incorporating E × B velocity terms on inversion results during the periods of ionospheric calm and geomagnetic storm is analyzed. The PINN‐SAMI3 achieves good inversion results even using sparse data in comparison to the traditional artificial neural networks (ANN). The framework will contribute to advance the future space weather prediction capability with artificial intelligence (AI).

Reconstruction and analysis of transient evolution images of laser-produced plasma plumes.

We introduce a method for the analysis and simulation of transient images of laser-produced plasma (LPP) plumes. This method comprises three steps: (i) calculating the two-dimensional distribution of plasma parameters using a radiation hydrodynamics model, (ii) constructing radiation paths through ray tracing, and (iii) solving the radiation transport equation along these paths. In our simulations, we have meticulously considered factors that could influence the imaging results, including the quantum efficiency to different radiation wavelengths, the imaging lens' transmittance, the target surface's reflectivity, and the absorption, emission, and scattering quantum effect of the detector processes occurring in the plasma. We applied this method to analyze and simulate the transient images of aluminum plasma plumes in a background air environment at a pressure of 2000 Pa. The results demonstrate that our method not only produces simulated images that align with experimental results but also provides a reliable distribution of plasma state parameters and clearly identifies the ion species radiating in different bands. Given its capability in transient image reconstruction and its adaptability as a tool for spectral simulation and analysis of LPPs, we believe this method holds significant potential for spectral diagnostics in fields such as laser-induced breakdown spectroscopy, extreme ultraviolet lithography sources, and high-energy-density physics, among others.

Numerical optimization of dielectric properties to achieve process uniformity in capacitively coupled plasma reactors

This paper presents the results of our numerical analysis to optimize the dielectric properties to achieve process uniformity in the thin film deposition process using capacitively coupled plasma. The difference in the plasma density distribution was analyzed by changing the wafer material from silicon to quartz (or Teflon). Similarly, aluminum was compared with aluminum nitride as the electrode material, and the sidewall material was varied from quartz to a perfect dielectric to study the effect on the plasma characteristics. A two-dimensional self-consistent fluid model was used to analyze the spatial distribution of the plasma parameters. In terms of the process conditions, the gas pressure was set to 400 Pa, the input power was fixed to 100 W, and a radio frequency of 13.56 MHz was used. SiH4/Ar was used as the gas mixture, and these conditions were used as input for numerical simulations of the deposition state of the hydrogenated amorphous silicon layer. The radial spatial distribution of plasma parameters was confirmed to be modified by dielectric elements with low dielectric constants regardless of the type of element. Despite the thin wafer thickness, the use of a wafer with low permittivity weakens the electric field near the electrode edge due to the stronger surface charging effect. Additionally, by changing the material of the sidewall to a perfect dielectric, a more uniform distribution of plasma could be obtained. This is achieved as the peak values of the plasma parameters are located away from the wafer edge. Interestingly, the case in which half of the sidewall was specified as comprising a perfect dielectric and the other half quartz had a more uniform distribution than the case in which the sidewalls consisted entirely of a perfect dielectric.

Development of charge-discharge circuitry based on supercapacitor and its application to limiter probe diagnostics in EAST

The EAST limiter probe is installed on the front surface of guard limiter, which consists of two columns and can operate in floating potential mode, ion saturation current mode, and swept single-probe mode simultaneously. When Langmuir probe operates in the ion saturation current mode, it requires a stable biasing voltage. To meet this requirement, a large capacitor is used to provide a biasing voltage for the probe. Comparing with the 9 V dry batteries that are commonly used in magnetic confinement fusion devices, employing a large capacitor offers advantages such as flexible voltage adjustment, easy maintenance, and environmental friendliness. Therefore, we have designed and tested a complete set of supercapacitor charge-discharge control circuitry. In this work, a control software is developed for the supercapacitor charge-discharge control circuitry based on the Python language to enable the remote and automatic controlling of the circuitry operation. As demonstrated in experiments, the capacitor charge-discharge control circuitry can supply stable biasing voltage output for the probe under long-pulse discharge, and it is workable in complex electromagnetic environment of magnetic confinement fusion device. By implementing the supercapacitor charge-discharge control circuitry in EAST limiter probe diagnostics, the three-dimensional distributions of plasma parameters are measured, such as ion saturation current, floating potential, electron temperature, and plasma density. In a lower hybrid wave (LHW) heating experiment, the 2.45 GHz LHW is found to generate larger electron density than the 4.6 GHz LHW, and the largest electron density appears when both the 2.45 GHz and 4.6 GHz LHWs are turned on simultaneously. These experimental results confirm that supercapacitor charge-discharge control circuitry can be operated reliably and stably.

Electron extraction mechanism of magnet array microwave discharge neutralizer

Microwave discharge neutralizer is an important part of microwave discharge ion thruster system, which plays a vital role in maintaining potential balance between spacecraft and neutralizing ion beam. Its electron extraction property directly affects the operation condition of ion thruster system. In order to break through the power limit of miniature microwave discharge ion thruster, a magnet array microwave discharge ion thruster system is designed and tested. In the experiment on finalizing magnetic field structure of magnet array microwave discharge neutralizer, an interesting phenomenon is found that the <i>I</i>-<i>V</i> curves of electron current, after rotating the magnetic array orientation, are very different. Defining forward direction of magnet array can normally extract electrons, then backward direction of magnet array can hardly extract electrons. Because the diameter of discharge chamber is only 10 mm, it is too small to perform Langmuir probe diagnosis. And thus, an integrative particle-in-cell method is used to simulate the neutralizer operation processes of two different magnetic field structures, and for the sake of accuracy, real vacuum permittivity is used. The simulation results show good consistence with experimental phenomenon. In the initial discharge process, it is found that the magnetic field gradient leads to different plasma distributions; in electron extraction process, it is found that the potential distribution near the orifice determines the electron extraction property of the neutralizer. Through comparing the plasma parameter distributions under different magnetic field structures and operating voltages, an assumption that the ion is an important factor in electron extraction process is proposed. Then, a simulation that ions disappear artificially outside the orifice is conducted, and the simulation results show that electrons cannot be effectively extracted without ions near the orifice. According to the simulation and experiment results, two necessary conditions are summarized for electron extraction of the neutralizer. The first condition is magnetic field structure: the magnetic field gradient should point towards the orifice to guide plasma migration towards the orifice, the second one is potential distribution: there should be enough ions to lift the potential near the orifice for reducing or breaking the potential well. These two conditions can help understand the electron extraction mechanism of microwave discharge neutralizer and provide theoretical reference for optimizing the performance of neutralizer in future.

Optical emission spectroscopy of fiber laser sustained Xe plasma

Laser-sustained plasma (LSP), a unique method of obtaining high brightness broadband light sources, has been used for rapid optical inspection of wafer defects and has thus attracted great interest. Then Xe plasma sustained under high pressure by a continuous fiber laser was investigated using optical emission spectroscopy (OES). Emission spectra of spatial integration diagnosis have shown that with the increase of laser power and the decrease of Gaussian beam focusing number F, the electron temperature fitted by Boltzmann plot method increased from 0.45 eV to 0.85 eV, the corresponding electron density was roughly an order of magnitude of 1016-1017 cm-3, and the calculated absorption coefficient of plasma was distributed in 0.9–1.5 cm-1. To further analyze the spatial distribution of plasma parameters, the spatial resolved OES of LSP was acquired, and the two-dimensional electron temperature and electron density were determined. The non-uniform distribution of the plasma parameters was analyzed due to the existence of thermal gravity convection and forced convection. The serious self-reversal of emission lines of 881.94 nm and 823.16 nm was observed and analyzed.

Numerical model of a gaseous inductive discharge in oxygen, taking into account the complete scheme of the vibrational kinetics of O2 molecules

In this work, the two-dimensional model of inductively coupled plasma discharge in oxygen was developed. The model includes hydrodynamic equations in drift-diffusion approximation for describing the kinetics of charged (electrons and ions) and neutral plasma particles, Maxwell’s equations for electromagnetic fields, and equations for the temperature and neutral gas flow as well as a detailed scheme of plasma-chemical reactions. The model was tested against theoretical and experimental data in a simple cylindrical chamber. The electron density and temperature distributions were obtained over a wide range of powers deposited in the plasma (100–500 W) and compared with literature data. Also, the complete scheme of the vibrational kinetics of O2 molecules was included in the model. The vibrational distribution function was calculated in low-pressure inductive discharge as well as spatial distributions of plasma parameters (density and temperature of electrons, excited components, neutral gas temperature, etc.) and flows of charged and active neutral particles at the reactor walls.

Simulation of argon-excited microwave plasma reactor for green energy and CO2 conversion application

Microwave plasma as a potential tool to convert CO2 has been extensively studied in recent years. A simulated study on the plasma parameters via the variation of the operating pressure of a microwave plasma model has been performed in this study. The establishment of the model was based on the finite element method to analyse the spatial distribution of plasma parameters in the plasma torch over a period of time. Plasma parameters such as electron potential, density, and temperature were investigated at three different pressures, and the growth of electron potential and density were associated with time. The distribution of molecular ions was observed to be located more on the enter port of the microwave or waveguide near the location of the magnetron at the initial stage. The electron density was found to be constant after it reached maximum value for all the determined pressures. However, the electron temperature behaved differently as compared to the electron potential and density, the distribution of high electron temperature did not enhance during the processing time. The analysis of microwave plasma parameters is beneficial for plasma reactor designing, particularly for CO2 conversion.

Two-Dimensional Distribution of Plasma Electric Potential in the T-10 Tokamak

Heavy ion beam probe (HIBP) is a unique plasma diagnostics that makes it possible to measure the electric potential φ of high-temperature plasma and its fluctuations y, as well as the density ne and poloidal magnetic field Bpol fluctuations. Position of the point of performing measurements in the plasma vertical cross-section depends on the beam energy and angle of its entrance into the plasma. The variation of these two parameters makes it possible to construct a two-dimensional (2D) detector grid, which covers the domain of possible measurements. The measurement results obtained in the detector grid points provide for constructing 2D distributions of plasma parameters. For the OH and ECRH stages of the T-10 tokamak shots, 2D distributions of the plasma electric potential are presented for the regime with the on-axis magnetic field of Bt = 2.2 T, plasma current of Ipl = 230 kA, line-average density of ne ≈ 1.1 × 1019 m–3 and off-axis ECRH power of PECRH = 1.7 MW.

Characteristics of very high-frequency plasma with an underexpanded supersonic gas jet

Very high-frequency (VHF) plasma generated with a supersonic gas jet, which is attractive for high-speed and low-damage film deposition in plasma enhanced chemical vapour deposition (PECVD), were investigated experimentally and theoretically. When the gas flow rate was changed under a background pressure in the Torr regime, a unique beam-shaped plasma was clearly observed in the region where an underexpanded jet was generated. It was found through plasma measurement that the plasma parameters are strongly influenced by the spatial structure of the underexpanded gas jet. In particular, the ionization rate was greatly changed according to the local change of gas pressure due to the jet, and the temperature and density of electrons changed by double and one order of magnitude, respectively. These phenomena are considered to be useful to locally control the spatial distribution of plasma parameters.

Modelling the spatial-temporal expansion of laser-produced tin (Sn) plasma with femtosecond laser

In this study, the 1-D hydrodynamic code (MED103) has been used to simulate the Tin (Sn) plasma in space and time with 400 cells as mesh and 10 ns simulation time that is produced by laser with the pulse of 500 fs and its wavelength of 1064 nm. Unique radiation sources of extreme ultraviolet and soft X-ray emissions can be generated from the high ions of laser-produced heavy element plasmas. The spatial-temporal distribution of Sn plasma parameters was studied when a laser pulse was focused on a target to 100 µm diameter with the intensity of 1.27 * 1015 w/cm2. There are two peaks of pressure, first inside the target after laser pulse time and the other close to the surface of the target at a time of 8 ns which is higher than 30 ≈ Mbar. The pressure is still high during simulation time. During and after the laser pulse time, the electron and ion temperature reaches maximum value but their values are not equal.

Coupled KIPP-EDGE2D modeling of parallel transport in the SOL and divertor plasma for the ITER baseline scenario

The KInetic code for Plasma Periphery (KIPP) models the parallel (along magnetic field lines) propagation of charged particles in the scrape-off layer (SOL) and divertor of tokamaks. An iterative coupling between KIPP and a 2D edge fluid code, EDGE2D, which in turn is coupled to the Monte Carlo solver for neutrals, EIRENE, was used to achieve a converged KIPP-EDGE2D-EIRENE solution. In the iterative coupling algorithm, KIPP transfers kinetic parallel electron and ion heat conductivities to EDGE2D, whereas EDGE2D returns to KIPP 2D distributions of macroscopic plasma parameters across the computations grid. The initial EDGE2D-EIRENE solution simulated the SOL and divertor plasma of the ITER inter-edge localized mode (ELM) baseline scenario. This work employs the same methodology as an earlier study based on the analysis of JET high radiative H-mode conditions, with strong nitrogen injection leading to partial detachment at divertor targets (Chankin et al 2022 Plasma Phys. Control. Fusion 64 095007). The results are qualitatively similar to those of the JET study in demonstrating the strong heat flux limiting effect, together with the rise in electron and ion temperatures in the main SOL. At the same time, the kinetic effects of the parallel propagation of charged particles are not expected to drastically change the target power deposition at divertor targets calculated by EDGE2D-EIRENE alone.

Simulation of DC glow discharge plasma with free-moving dust particles in the radial direction

A self-consistent fluid model is developed to investigate the radial distributions of dusty plasma parameters in a DC glow discharge, in which the extended fluid approach of plasma particles and the transport equations of dust particles are coupled. The electrical interaction between charged dust particles is considered in the model. The time evolution of radial distributions of dust density, plasma density, the radial component of electric field and the forces acting on dust particles when dust density tends to be stable, are obtained and analyzed under different discharge currents and dust particle radii. It is shown that the dust density structure is determined mainly by the radial electrostatic force, thermophoretic force and ion drag force in the discharge tube, and both discharge current and dust particle radius have an obvious effect on the transport processes of dust particles. The dust particles gather in the central region of the discharge tube for low discharge current and small dust radius, then dust voids are formed and become wider when the discharge current and dust radius increase. The plasma parameters in the dust gathering region are obviously affected by the dust particles due to the charging processes of electrons and ions to the dust surface.

Energy and particle balance during plasma detachment in a long-leg divertor configuration

Comprehensive studies of energy and particle balances in the transition to plasma detachment in an alternative divertor configuration with long outer legs are shown. Numerical simulations are performed with the 2D code suite SOLPS 4.3, using a disconnected double null grid with narrow, tightly baffled long poloidal leg divertors at the outer lower target and outer upper target. A particle count scan is performed using the ‘closed gas box’ model, where the tunable parameter in the simulations is the total number of deuterium particles in the simulation space and all other parameters are held fixed, including a constant input power and trace neon impurity radiation, to assess the physics of the transition to detachment in the system as the particle count increases. Three main aspects of the physics of divertor detachment are addressed: the criteria for the local onset of divertor detachment in each of the divertors, the distribution of heat flux and other plasma parameters between the four divertors as each divertor transitions to detachment, and the role of perpendicular transport in the transition to the detached regime. A synergistic mechanism by which the cross-field transport is reduced by factors associated with the onset of plasma recombination effects is identified. These results are compared to the existing understanding of the physics of the transition to plasma detachment in standard divertors.

Statistical Analysis of Interplanetary Shocks from Mercury to Jupiter

In situ observations of interplanetary (IP) coronal mass ejections (ICMEs) and IP shocks are important to study as they are the main components of solar activity. Hundreds of IP shocks have been detected by various space missions at different times and heliocentric distances. Some of these are followed by clearly identified drivers, while some others are not. In this study, we carry out a statistical analysis of the distributions of plasma and magnetic parameters of the IP shocks recorded at various distances to the Sun. We classify the shocks according to the heliocentric distance, namely from 0.29 to 0.99 AU (Helios-1/2); near 1 AU (Wind, ACE, and STEREO-A/B); and from 1.35 to 5.4 AU (Ulysses). We also differentiate the IP shocks into two populations, those with a detected ICME and those without one. As expected, we find that there are no significant differences in the results from spacecraft positioned at 1 AU. Moreover, the distributions of shock parameters, as well as the shock normal, have no significant variations with the heliocentric distance. Additionally, we investigate how the number of shocks associated with stream-interaction regions (SIRs) increases with distance in the proportion to ICME/shocks. From 1 to 5 AU, SIRs/ shock occurrence increases slightly from 21% to 34%; in contrast, ICME/shock occurrence decreases from 47% to 17%. We also find indication of an asymmetry induced by the Parker spiral for SIRs and none for ICMEs.

Simplified Plasmadynamics Model of a Coaxial Self-Field Plasma Accelerator

A simplified plasmadynamics model is presented that examines radial and axial dependence of the current sheet structure of a coaxial quasi-steady self-field plasma accelerator, dominated by electromagnetic forces. Two radial electric field distributions are considered as limiting cases. In the first case, constant current flows between constant-radius electrodes; in the second case, constant current flows between electrodes and also extends downstream of the electrodes. Calculations for Teflon () plasma show the distribution of plasma parameters inside the current sheet, as well as terminal values for kinetic efficiency, voltage, and impedance for both distributions. Evaluation of the validity of simplifying assumptions is presented, as is the behavior of previously developed accelerators as interpreted by the model.

Influence of neutral gas supply position on wall erosion of Hall thruster studied by particle-in-cell simulation

In this work, we have carried out a simulation study on the discharge process of Hall thrusters under the conditions of different neutral gas radial supply positions based on the particle-in-cell (PIC) and Monte Carlo collision (MCC) methods. This paper compares the two-dimensional (2D) distributions of neutral gas, plasma and wall erosion-related parameters under different neutral gas supply positions. The comparison results show that the change of the neutral gas supply position affects the radial distribution uniformity of the neutral gas and plasma in the channel. From the comparison of the density peaks, it can be found that the neutral gas density and the plasma density peak under the upper gas supply condition are relatively low, and the plasma density peak is 22.49% lower than the density peak under the middle gas supply condition. Meanwhile, as the radial position of the gas supply moves from the lower gas supply to the upper gas supply, the position of the ionization zone also gradually moves toward the anode. The results of erosion-related parameter distribution comparison show that the change of gas supply location has an obvious influence on erosion rate and erosion range. In terms of erosion rate, the wall erosion rate is relatively low under the upper gas supply condition, and the peak erosion rates of the inner and outer walls are 33.3% and 29.9% lower than those under the other two conditions. In terms of erosion range, as the gas supply position moves from the lower gas supply position to the upper gas supply position, the erosion range gradually increases from 5 to 7.5 mm.

Analysis of Effect of Ground Experiment Environment on Plasma Contactor Performance

The large difference in the working performance of a hollow cathode plasma contactor between the ground and actual on-orbit environments will cause difficulties in selecting a ground-test schemes to fully simulate the contactor real on-orbit characteristics. In this study, the effect of the simulated anode size and structure, the simulated anode surface state, the flow rate of background working gas, and the background plasma density on the emission characteristics and plume structure of the contactor are studied. Three self-made simulated anodes of different sizes and structures are applied in the ground experiments. The change of anode surface state (particularly the ability of absorbing electrons) is realized by dividing the self-made simulated anodes into four double-separated regions and alternatively electrically isolating them. An additional gas channel and an auxiliary contactor are used to create background working gas and a low-Earth-orbit plasma atmosphere, respectively. The voltage–current curves as well as the plasma parameter distributions at the contactor exit and in the far-field regions are determined under different regimes and working conditions. The relationship between the contactor’s emission characteristics and plume structure is clarified. The experimental results could provide useful information for instructing the contactor design and developing a real on-orbit experiment plan.

Study on the effect of discharge chamber length on the performance of electron cyclotron resonance ion thruster

Discharge chamber length is one of the factors in optimizing the electron cyclotron resonance ion thruster performance. It adjusts the distance between bulk plasma and grid system to change the plasma density upstream of the screen grid, which will affect the ion beam current and focusing state to achieve optimization purpose. However, new evidence shows the discharge chamber length plays an important role in ionization during ion beam extraction, which means that the effect of discharge chamber length on the performance of electron cyclotron resonance ion thruster should be reexamined. After applying grid voltages, another high electron temperature region located upstream of the screen grid is observed in the integrated simulation using particle-in-cell with Monte Carlo collision method, but it is not observed in the traditional discharge chamber simulation. It is believed in the paper that the high electron temperature region exists objectively, because the Child-Langmuir sheath will repel electrons moving towards screen grid back to magnetic mirrors again. Those electrons will gain energy from microwave, and finally form a high electron temperature region along the Child-Langmuir sheath. This phenomenon implies that discharge chamber length can adjust the high electron temperature distribution upstream of screen grid to affect the plasma generation. Therefore, in this work, the effect of discharge chamber length on discharge and ion beam performance is systematically studied by adopting the integrated simulation. In this paper, three ion thrusters with different discharge chamber lengths are simulated. Under the conditions of same magnetic field and operation parameters, the comparisons of electron energy gain, plasma parameter distributions and ion beam current among the three ion thrusters are conducted. The results show that shorter discharge chamber length has higher electron energy gain, plasma density and voltage, but smaller ion beam current. This abnormal phenomenon can also be seen experimentally. By analyzing the ionization rate inside the chamber, it can be seen that high-temperature electrons upstream of the screen grid have a significant contribution to ionization. And thus, a little bit longer discharge chamber length with lower plasma density inside the chamber has bigger ion beam current for having higher plasma density upstream of the screen grid. According to this phenomenon, an electron heating mode is proposed: electrons gain energy by reciprocating through the electron cyclotron resonance layer between the Child-Langmuir sheath and magnetic mirrors. This heating mode can be used as a supplement to the electronic constraints outside the magnetic mirrors to improve the energy utilization efficiency of the thruster, which can provide a new insight into the electron cyclotron resonance ion thruster design in the future.