Plasma Behavior Research Articles

Resolving multi-dimensional plasma phenomena in Hall thrusters using the reduced-order particle-in-cell scheme

Plasma in Hall thrusters exhibits a complex behavior, characterized by the interplay between various dominant processes in each of the thruster’s coordinates. The emergence of high-power Hall thrusters in the recent years and the design modifications intended to extend the lifetime of these devices have further amplified the three-dimensional nature of the plasma behavior. In this regard, the novel reduced-order particle-in-cell (PIC) scheme provides the possibility to resolve the multi-dimensional interactions in a Hall thruster at a computational cost up to two orders of magnitude lower than current multi-dimensional PIC simulations. To demonstrate this point, we present in this article the results from a series of pseudo-two-dimensional simulations we performed in three configurations: axial-azimuthal, azimuthal-radial, and axial-radial. We show that, in each configuration, the pseudo-2D PIC scheme provides a significantly improved picture of the involved physics compared to a one-dimensional PIC simulation and captures self-consistently the coupling between the plasma processes in different directions, notably similar to the observations from full-2D kinetic simulations.

Effect of nanodiamond concentration on the electrochemical behavior of plasma sprayed titanium-nanodiamond nanocomposite coatings

Current work intends to improve the corrosion performance of plasma sprayed titanium coating by reinforcing a carbon-based zero-dimensional nanomaterial: Nanodiamond (ND). Various composition (0.1, 0.5 and 1 wt%) of ND was reinforced in the Ti feedstock. XRD of the powders and coatings showed the presence of majorly Ti phase, only difference being the presence of oxide phase in the coatings. The electrochemical tests in 3.5 wt% NaCl solution showed a dual faceted effect of ND reinforcement on the corrosion behavior. The 0.1 wt% ND reinforcement in Ti matrix drastically decreased the corrosion rate to 3.162 mpy of the coating as compared to that of monolithic Ti coating having corrosion rate of 5.89 mpy due to filling up of pores and micro-cracks in the coating. On contrary, the corrosion rate of Ti-1 wt% ND coating dramatically increased to 5.148 mpy, attesting that higher ND (≥1 wt%) content might not be a right choice when corrosion resistance of matrix is concerned. Higher ND content initiates microgalvanic corrosion in the composites. Post corrosion studies were also carried out to show the effect of electrolyte as well as of ND content on the microstructure of the coating after corrosion. From this study, it can be deduced that ND addition might be an economical option if improving the corrosion resistance of the various engineering components are concerned, since a 0.1 wt% ND content is able to drastically improve the resistance of the coating.

Viscoelastic and Electromagnetic Materials with Nonlinear Memory.

A method is presented for generating free energies relating to nonlinear constitutive equations with memory from known free energies associated with hereditary linear theories. Some applications to viscoelastic solids and hereditary electrical conductors are presented. These new free energies are then used to obtain estimates for nonlinear integro-differential evolution problems describing the behavior of nonlinear plasmas with memory.

Effect of heat source parameters on weld formation and defects of oscillating laser-TIG hybrid welding in horizontal position

In this paper, a comparison study of the narrow gap horizontal welding characteristics of tungsten inert gas (TIG) welding, non-oscillating laser-TIG hybrid welding, and oscillating laser-TIG hybrid welding is presented. Weld forming tests were performed using various heat source mode parameters. The plasma behavior, the molten pool flow, and the keyhole behavior of these different heat source modes were observed. In addition, filling welding operations were performed, and the defect generation mechanism was analyzed. The results show that oscillating laser-TIG hybrid welding can improve weld formation effectively and suppress defects such as weld porosity and incomplete fusion. The coupling effect of the laser-TIG arc weakens as the oscillation amplitude and the distance between the laser and the tungsten electrode increase. The hybrid plasma generates periodic changes with the laser oscillation, which results in a more uniform energy distribution that improves the sidewall fusion and prevents the formation of large numbers of bubbles. The keyhole stirs the molten pool and drives the molten pool to scour the groove sidewall, which helps to improve the sidewall fusion and suppress pore formation. The oscillating laser-TIG hybrid welding process with an oscillation amplitude of 4 mm and a distance of 3 mm between the laser and the tungsten electrode obtained high-quality welds with good weld morphology.

Temperature-Dependent Wear Behavior of Air Plasma Sprayed Alumina and Alumina–Titania Composite Coatings

Temperature-Dependent Wear Behavior of Air Plasma Sprayed Alumina and Alumina–Titania Composite Coatings

High temperature oxidation behavior of thermal and plasma processed aluminide coated Ti6Al4V alloys

In this study, the high temperature cyclic oxidation behavior of thermal and plasma-treated aluminide coated Ti6Al4V alloy was investigated at 800 °C up to 360 h in 24 h cyclic exposures. The microstructural characteristics, phase analysis, morphological features, and microhardness of resultant oxidized samples were evaluated and compared with those of untreated Ti6Al4V alloy. The weight gain studies conducted from the cyclic oxidation tests revealed very minimal weight gain in plasma treated (PT) aluminide coated samples as compared to the thermal treated (TT) and uncoated (UC) samples. XRD results indicate that the UC samples oxidized at 800 °C exhibits the formation of a thick oxide layer consisting of only the rutile phase (TiO2). The TT and PT samples oxidized at 800 °C revealed presence of both alumina (Al2O3) and rutile (TiO2) phases. However, PT samples revealed stable α-Al2O3 phase whereas the TT samples showed metastable θ-Al2O3 phases in the oxide layer. The surface morphological features reveal that the oxide film formed on the surface of the PT samples had enough stability at 800 °C irrespective of the oxidation time. The PT samples exhibited higher hardness and improved oxidation resistance as compared to TT and UC samples. Increase in thermal stability, mechanical and oxidation properties of PT samples could be attributed to the formation of stable alumina (α-Al2O3) and presence of nanocrystalline aluminide phases (TiAl3 & TiAl2) in the diffusion layers during the oxidation tests. Therefore, a strong emphasis was placed on correlating the interfacial processes to the high temperature oxidation behavior.

Plasma characterization in CW and pulsed mode and its effect on beam current in 2.45 GHz ECR Ion source

Electron Cyclotron Resonance Ion Source (ECRIS) is used as a front end for Low Energy High Intensity Proton Accelerator (LEHIPA) at BARC. A 50 keV ECRIS is designed and developed for the proton ion beam for this accelerator. The key requirements of the ion source are beam current ∼ 10 – 15 mA and beam emittance ∼ 0.2 π mm-mrad. In the commissioning phase of LEHIPA, the ion source is operated in pulsed mode to mitigate the effect of thermal and radiation load. Measurements have been carried out to understand the behavior of pulsed plasma and its effect on ion beam. An Automated Langmuir Probe (ALP) and its associated circuit are designed and developed for this purpose. The ALP circuit consists of a voltage sweep generator, current sense circuit, and voltage sense circuit. The effect of microwave power and pulsed plasma duration on the plasma and the ion beam parameters have been studied. The plasma parameters are correlated with the beam parameters.

Multi-Objective Design Optimization of Cusped Field Thruster via Surrogate-Assisted Evolutionary Algorithms

Cusped field thrusters are an efficient cost-effective electric propulsion technology that offer promise for small spacecraft platforms. They offer various advantages, including simple design and low wall erosion, and hence long-life operation owing to high plasma confinement using permanent magnets over other electrostatic alternatives. Accurate physical modeling and performance characterization are crucial to achieve successful downscaling of cusped field thrusters while maintaining high performance. Multiobjective design optimization is performed by incorporating magnetic simulation coupled with an improved power balance model into evolutionary algorithms assisted by surrogate modeling, aiming to simultaneously maximize thrust, total efficiency, and specific impulse. Physical insights have been gained into key design factors to maximize thruster performance by probing into the plasma behavior inside the channel and the plume region. It has been found that altering the magnetic field distribution using an additional magnet can effectively enhance thruster performance by suppressing the plume divergence loss. Global sensitivity analysis has identified the anode current as the most influential design parameter on the performance parameters due to the active role it plays in the ionization process. Uncertainty analysis has found the considerable influence of the variations of anode potential and mass flow rate on those of thrust and specific impulse.

Comparative study of the aging behavior of plasma activated hexamethyldisiloxane-based plasma polymers and silicone elastomer thin films

The aging of plasma activated plasma polymer films has been studied to a limited extent, despite the recent application-oriented interest for these coatings. Therefore, the aging of plasma polymerized hexamethyldisiloxane (ppHMDSO) coatings that were subjected to helium or dry air plasma activation was investigated and compared to the aging of plasma activated silicone elastomer (S184) in this work. Water contact angle (WCA) measurements indicated that both materials reached a super-hydrophilic state after both plasma treatments. X-ray photoelectron spectroscopy (XPS) illustrated that this was the result of the introduction of a variety of oxygen-containing functionalities, while atomic force microscopy highlighted that the morphology was not significantly changed. The WCAs of the plasma activated ppHMDSO coating and S184 showed similar aging behavior, as the wettability of both materials significantly decreased. XPS measurements after 11 days of aging indicated that multiple aging processes were occurring in S184, while migration of oxidized short chain fragments was most important for the ppHMDSO coating. All these aged coatings could be silanized with 3-aminopropyltriethoxysilane, although differences in stability were observed. As such, this study provides additional insight in the chemical nature of activated plasma polymers and provides design principles for synthesizing plasma polymers with selective chemical functionalities.

Electron density and temperature of dual-frequency capacitively coupled argon plasma in two-dimensional distribution obtained and studied in experiment

Behaviors of plasma in spatial distributions are vital for understanding physical mechanisms of low pressure capacitively coupled discharges. However, due to the lack of simple and reliable diagnostic techniques, few experimental studies have focused on two-dimensional distributions of plasma. Recently, we have developed a new method for rapid two-dimensional plasma diagnosis. With this method, the dual-frequency capacitively coupled plasma, an important plasma commonly used in etching, is systematically studied. Three circumstances are presented here: In case I, the plasma discharge was driven by a radio-frequency source; in case II, two radio-frequency sources were applied to one electrode; and in case III, such sources were applied to two separate electrodes. Results show that both the emission intensity and electron density in case III are higher than those in case II, and because the absolute value of the DC self-bias voltage is smaller, the structure of axial discharge is more symmetric in case III. For the asymmetrically capacitive discharges (cases I and II), the position of the maximum axial electron density is close to the powered electrode due to the presence of the DC self-bias voltage. As the low-frequency power increases or gas pressure decreases, the position of the maximum axial electron density moves gradually toward the grounded electrode because of the enlarged thickness of the sheath. However, high-frequency power has a limited influence on the position of the maximum axial electron density. The radial distribution of plasma is more uniform when plasma density is relatively low. For a higher plasma density situation, the center-peaked density profile results from the higher power deposition at the electrode center and/or more local charged particle dynamics. In addition, under the same discharge conditions, a lower electrode gap is favorable for the occurrence of the α-γ mode transition.

Impact of coherent mode on divertor particle and heat flux in a type I ELMy H mode plasma on EAST tokamak

The paper investigates the effect of pedestal turbulence, i.e. coherent mode (CM), on the divertor total particle flux, the particle flux distribution and heat flux distribution, and their decay lengths in the scrape-off layer (SOL) region on EAST tokamak. The experimental evidence indicates the coherence between the pedestal CM and the divertor particle flux fluctuation, which implies that the pedestal CM can affect the divertor plasma behavior. The increase of the particle flux decay length correlates with the density radial decay length (λ n,SOL) in the SOL region where the λ n,SOL is largely affected by the change of pedestal CM amplitude. A quantitative statistical analysis shows that the divertor total particle flux and in the SOL region increase with increasing amplitude of the electron density fluctuation and the electron temperature fluctuation induced by the pedestal CM. The temporal decay process of the total particle flux is interrupted by the appearance of CM at the pedestal. Meanwhile, the spatial distributions of the divertor particle flux and heat flux are enhanced when the pedestal CM appears, which are observed in both the upper single null and lower single null configurations.

Low-temperature plasma simulation based on physics-informed neural networks: Frameworks and preliminary applications

Plasma simulation is an important, and sometimes the only, approach to investigating plasma behavior. In this work, we propose two general artificial-intelligence-driven frameworks for low-temperature plasma simulation: Coefficient-Subnet Physics-Informed Neural Network (CS-PINN) and Runge–Kutta Physics-Informed Neural Network (RK-PINN). CS-PINN uses either a neural network or an interpolation function (e.g., spline function) as the subnet to approximate solution-dependent coefficients (e.g., electron-impact cross sections, thermodynamic properties, transport coefficients, etc.) in plasma equations. Based on this, RK-PINN incorporates the implicit Runge–Kutta formalism in neural networks to achieve a large-time step prediction of transient plasmas. Both CS-PINN and RK-PINN learn the complex non-linear relationship mapping from spatiotemporal space to the equation's solution. Based on these two frameworks, we demonstrate preliminary applications in four cases covering plasma kinetic and fluid modeling. The results verify that both CS-PINN and RK-PINN have good performance in solving plasma equations. Moreover, RK-PINN has the ability to yield a good solution for transient plasma simulation with not only large time steps but also limited noisy sensing data.

A Fourier transformation based UGKS for Vlasov–Poisson equations in cylindrical coordinates [formula omitted

A Fourier transformation based unified gas-kinetic scheme (UGKS) is proposed to simulate the kinetic behaviors of plasma in cylindrical coordinates (r,θ,vr,vθ), the model is depicted by Vlasov–Poisson equations coupled with Bhatnagar–Gross–Krook(BGK) collision term. Fourier transformation is applied to the equations for θ and a series of equations are gotten. Based on Strang-splitting strategy, Vlasov equations are divided into two parts, the transport-collision part solved by a multiscale gas-kinetic scheme, and acceleration part solved by Runge–Kutta method. The algorithm is applied on charge separation problem at plasma edge and Z-pinch configuration. Numerical results show our scheme can give a clear kinetic picture of plasma in 2D phase space, and also can capture the process from non-equilibrium to equilibrium state by Coulomb collisions.

Characterization and investigation of the unique plasma behavior caused by variable driving frequencies in the formation of cold atmospheric plasma

The study presents the characterization of a novel variable frequency (11–50 kHz) Atmospheric Pressure Plasma Jet (APPJ) source and comparison of the results with 13.56 MHz source, in terms of species generation and species temperature. The behavior of variable frequency APPJ at different frequency regimes was investigated using optical emission spectroscopy to understand the interaction with the ambient environment. The quantitative dependence of the radical generation on driving frequency and time of treatment was also analyzed by direct synthesis of H2O2 by plasma-water interaction. The plasma formed with a kHz driving frequency had a low treatment temperature, which was suitable for biological species, but the plasma generated with a 13.56 MHz driving frequency had a substantially higher radical density than the kHz plasma. As a result, the APPJ device's ability to tune the radical density and treatment temperature with a change in kHz frequency has been demonstrated.

Structural, mechanical and electrochemical properties of spark plasma sintered Ti-30Ta alloys

Ti-Ta alloys are choice materials for bio-medical applications, but obtaining tailormade material properties through using spark plasma sintering (SPS) fabrication exhibits potential challenges. The effects of sintering temperature, pressure and holding time on the microstructural, crystallographic, mechanical and corrosion behaviour of spark plasma sintered Ti-30Ta alloys were investigated. Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffractometry, microhardness and instrumented nanoindentation were used for the investigation. Microstructures obtained include martensite plates (alpha-Ti phases), beta-Ti phases, as well as significant volume of beta-Ta phases. Notable variation in crystal structure, mechanical properties and electrochemical behaviour were recorded. Generally, the materials exhibited high densification (>98%), improved micro-and nano-indentation hardness (>500 Hv), and elastic moduli (>40 GPa). Average Oxygen content of the sintered samples was 0.0106%. The measured properties of the sintered Ti-30Ta alloys suggest they can be efficient for applications in biomedical technologies.

Divertor plasma behaviors with neon seeding at different locations on EAST with ITER-like divertor

For the problem of excessively high divertor heat flux, active impurity seeding is an effective method to radiate the plasma energy reaching the divertor and thus achieve the divertor detachment. Neon is a very effective radiation impurity on many current tokamaks, which is also a candidate species to be applied on ITER. In the EAST 2019 experimental campaign, a series of experiments were performed by seeding a mixture of neon and deuterium (Ne-D2) for detachment and core-edge-divertor integration in H-mode plasmas. The divertor partial detachment with high-confinement core plasma has been achieved by using Ne-D2 seeding in EAST with ITER-like tungsten divertor. Both the plasma stored energy and H 98,y2 > 1.1 are maintained, with the divertor electron temperature, heat flux and the surface temperature near the strike point being all significantly reduced. The differences between Ne-D2 seeding at the scrape-off layer (SOL) upstream and downstream have been experimentally investigated in detail. It is found that impurity seeding at SOL downstream is more beneficial to reducing the divertor electron temperature and peak heat flux. By comparison with experiments using divertor D2 fueling, it is further demonstrated that gas seeding in the SOL downstream will enrich more particles near the strike point, while the seeding in the SOL upstream will influence the entire outer target more evenly. Furthermore, in most of the experiments, gas seeding does not cause obvious toroidal asymmetry in the divertor plasma. However, when D2 is injected in an amount similar to that used to build the plasma, it causes the particle flux near the gas-puff to increase locally, i.e., much more than that at the toroidal location far from the gas-puff location. It is a competition between particle source and transport. When the particle source is stronger, it will naturally increase the local particles. In addition, dedicated experiments with different poloidal distances between impurity seeding and strike point on the radiation ability were carried out. Both experimental results and SOLPS simulation show that the seeding close to the strike point is more conducive to neon ionization and energy radiation.

Experimental investigation of current jumps in linear geometry hot cathode ionization gauges in strong magnetic fields

In magnetic confinement nuclear fusion, neutral gas in the plasma edge region plays an important role for plasma fuelling and plasma wall interaction and thus influences the overall plasma behaviour. The ASDEX pressure gauge is a diagnostic instrument designed to provide local and temporally highly resolved measurements of the neutral gas flux density within the strong magnetic fields of fusion devices. It is a hot cathode ionization gauge with a linear geometry. Its function principle relies on the measurement of an ion current, caused by oscillating electrons in the gauge which ionize the neutral gas. Anomalous jumps in the ion current of up to 30% have been observed during gauge operation in the tokamak ASDEX Upgrade and the stellarator Wendelstein 7-X, which introduces an error in the measurement. This paper describes for the first time the characterization of these jumps over the broad operational space. Parameter dependencies on pressure, electron current, electrode potentials and magnetic field angle are discussed. The appearance of electrostatic oscillations with frequencies in the range of 160MHz to 350MHz which are associated with the current jumps has been discovered. The frequency of these oscillations was found to scale with the oscillation frequency of the electron motion inside the gauge. Potential physical mechanisms to explain the jumps are discussed.

Exploring the electrochemical behaviour of DC glow discharge plasma exposed activated bamboo charcoal incorporated with FePO4 nanoparticles in energy storage applications

ABSTRACT FePO4 active material has a single-phase response with a significant number of charge carriers, to attain the optimum kinetics and three-dimensional ion migration. The Pyrolysis method was used for the preparation and activation of the Bamboo Charcoal (BCC). The surface properties like wettability, adhesion and conductivity were enhanced by the exposure of DC glow discharge plasma. FePO4 was prepared by hydrothermal method and the composite of FePO4/plasma treated BCC was made using pestle mortar. This work discusses the electrochemical behaviour of pure FePO4 and composite of FePO4/plasma-treated BCC was analysed with different electrolytes at different scan rates. If compared, the FePO4/plasma-treated BCC material was seen to have high specific capacitance/capacity and b-value was shifted from capacitive to diffusive. These findings suggested that FePO4/plasma exposed BCC could be a potential cathode material for energy storage devices.

CMAS attack behavior of air plasma sprayed thermal barrier coatings with big pores

Previous studies indicated that big globular pores in air plasma sprayed (APS) thermal barrier coatings (TBCs) are more likely to remain after calcium-magnesium-alumino-silicates (CMAS) attack than are small ones. In this research, therefore, the CMAS attack behavior of an APS TBC with more big globular pores was investigated. It was demonstrated that the more-big-globular-pores APS TBC exhibited better resistance to exfoliation and intergranular corrosion, and chemical degradation than normal APS TBCs, while its pores can be easily filled by CMAS. Analysis on pore structures and CMAS infiltration characteristics indicated that the morphologies of the transition regions between the globular and the crack network pores may play an import role in determining the CMAS filling behavior for globular pores in APS TBCs.

The behavior of plasma and space-charge waves represented by nonlinear mathematical models

In this study, traveling wave solutions are obtained by applying the modified exponential function method (MEFM) to the conformable time-fractional (3+1)-dimensional Zakharov-Kuznetsov (FZK) and the conformable time-fractional Symmetric Regularized Long Wave (SRLW) equations. In order to better understand the physical interpretations of the mathematical models represented by these two equations, 3D, contour, density and 2D graphics were plotted with the help of appropriate parameters. Thus, it has been shown that the modified exponential function method is effective in investigating the solutions of the conformable time-fractional (3+1)-dimensional FZK and the conformable time-fractional SRLW equations.