Plasma Behavior Research Articles

Enhancing microstructure, nanomechanical and anti-wear characteristics of spark plasma sintered Ti6Al4V alloy via nickel-silicon carbide addition

This study examines the nanomechanical and anti-wear behaviour of spark plasma sintered Ti6Al4V matrix composites reinforced with Ni and SiC particles. Microstructural analysis revealed the in-situ formation of the hard TiC, Ti3SiC2 and Ti5Si3 phases within the metal matrix. Nanoindentation analysis revealed that the composite containing 10 wt% SiC (TNi10SiC) exhibited significantly higher nanohardness (about 10.3 GPa) and elastic modulus (∼ 177.7 GPa) than the unreinforced Ti6Al4V alloy (sample T). The improved nanomechanical performance of the composites was attributed to the load-carrying capacity of the hard, in-situ formed reinforcement phases. The anti-wear characteristics of the composites showed that TNi5SiC composite displayed superior wear resistance with a specific wear rate of 4.75 ± 0.34 x 10-4 mm3/Nm and 2.15 ± 0.34 x 10-4 mm3/Nm under an applied loads of 10 N and 20 N, respectively, among the sintered samples. This represents about 67% and 29% reduction in specific wear rate relative to sample T. This enhanced tribological behaviour was ascribed to the increased surface hardness, the formation of a stable transfer layer, and the reduction in direct asperity contact at the sliding interfaces. However, reinforcement pull-out aggravates abrasive wear and leads to a higher specific wear rate for TNi10SiC composite. This work provides valuable information for advancing Ti6Al4V-based composites for enhanced structural and wear-resistant applications.

Measurement of spherical tokamak plasma compression in a PCS-16 magnetized target fusion experiment

Abstract A sequence of magnetized target fusion devices built by General Fusion has compressed magnetically confined deuterium plasmas inside imploding aluminum liners. Here we describe the best-performing compression experiment, PCS-16, which was the fifth of the most recent experiments that compressed a spherical tokamak plasma configuration. In PCS-16, the plasma remained axisymmetric with δ B pol / B pol < 20 % to a high radial compression factor ( C R > 8 ) with significant poloidal flux conservation (77% up to C R = 1.7, and ≈ 30 % up to C R = 8.65 ) and a total compression time of 167 μ s . Magnetic energy of the plasma increased from 0.96 kJ poloidal and 17 kJ toroidal to a peak of 1.14 kJ poloidal and 29.9 kJ toroidal during the compression, while the thermal energy was in the range of 350 ± 25 J. Plasma equilibrium was a low-β state with β tor ≈ 4 % and β pol ≈ 15 % . Ingress of impurities from the lithium-coated aluminum wall was not the dominant effect. Neutron yield from D-D fusion increased significantly during compression. Thermodynamics during the early phase of compression ( C R < 1.7 ) were consistent with increasing Ohmic heating of the electrons due to a geometric increase in the current density at near-constant resistivity, and with increasing ion cooling that approximately matched ion compression heating power. Ion cooling by electrons was significant because the electrons were much cooler than the ions ( T e = 200 eV , T i = 600 eV ). Magnetohydrodynamic simulations were used to model the emergence of instabilities that increase electron thermal transport in the final phase of compression. Conditions for ideal stability were actively maintained during compression through a current ramp applied to the central shaft and, after this current ramp reached its peak two-thirds of the way through compression, we measured a transition in plasma behavior across multiple diagnostics.

Lattice Boltzmann simulation of direct-current glow discharge at low pressure

To analyze electro-hydrodynamic behavior of low pressure direct-current glow discharge plasma, we propose a numerical model based on the lattice Boltzmann method and the drift-diffusion theory of gas discharge. In our model, three plasma species (excited species, electrons and ions) are considered with eight elementary chemical reactions among them and standard lattice Boltzmann method, finite difference-lattice Boltzmann method and finite difference method are employed for electrons, heavy species (ions and excited species) and electric potential, respectively. The proposed model introduces a unique coupling scheme between electrons and heavy species using a consistent time step and grid, enhancing accuracy and stability of numerical simulations. Our model is applied to one- and two-dimensional analyses of glow discharge, and the results are in good agreement with those from previous works.

Microstructural Evolution and Sintering Behavior of Supersonic Atmospheric Plasma Sprayed Multi-modal YSZ Coating

Microstructural Evolution and Sintering Behavior of Supersonic Atmospheric Plasma Sprayed Multi-modal YSZ Coating

Enhanced ablation resistance and mechanical behavior of spark plasma sintered ZrB2-SiC composites with TiC addition

The study evaluated the ablation resistance and mechanical behavior of spark plasma sintered ZrB2-25 vol% SiC-TiC (5–15 vol%) composites. The addition of TiC improved ablation resistance by promoting the formation of ZrO2.TiO2 and TiO2 phases on the oxidized composites. The ZrB2-25 vol% SiC-15 vol% TiC composite exhibited the lowest mass ablation rate of 0.11 mg/s and maximum fracture toughness of 5.8±0.29 MPa.m0.5. After ablation, SiC particle pull-out, crack deflection and crack bridging were identified as the primary toughening mechanisms. The maximum microhardness of 23.01±1.18 GPa and compressive strength of 1688.2±75.5 MPa were obtained for the ZrB2-25 vol% SiC-10 vol% TiC composite, which correspond to 92.86 % and 94.31 % of their respective maximum values prior to ablation. Furthermore, nanoindentation studies revealed significant improvements in both elastic modulus and nanohardness with the addition of TiC due to reduction in porosity and refinement in SiC grain size. After ablation, the elastic modulus and nanohardness reduced. However, the ZrB2-25 vol% SiC-10 vol% TiC composite retained a maximum elastic modulus of 433.61 GPa and nano-hardness of 21.88 GPa. The oxidation behavior of ZrB2-SiC composites containing TiC was analyzed at 1500°C for 6 hours in air. The TiC-containing composite exhibited lower mass gain, lower parabolic oxidation rate constant and a thin oxide layer compared to the ZrB2-SiC composites.

Numerical study of turbulent eddy self-interaction in tokamaks with low magnetic shear. Part I: Linear simulations

Abstract This study examines the impact of low and zero magnetic shear, along with rational values of safety factor, on linear mode behavior in tokamak plasmas. We focus on how magnetic field line topology and parallel domain length influence linear mode structures and growth rates as magnetic shear decreases. Our results
show that as magnetic shear is reduced to low values, linear modes can transition between different branches, significantly affecting their characteristics. At zero magnetic shear, accurate modeling requires precisely capturing magnetic topology, as small deviations near rational surfaces can greatly impact growth rates. These findings are extended to nonlinear simulations in a companion paper (Volčokas, 2024), revealing that long turbulent eddies and magnetic field line topology play a crucial role in turbulence self-interaction and plasma transport.

Single-shot ultrafast imaging of plasma dynamics induced by dual-angle ultrashort laser pulses with subpicosecond delay

Spatiotemporal manipulation of ultrashort laser pulses is crucial for enhancing laser processing and phonon generation. Optimization of these applications requires ultrafast visualization of the underlying processes. In this study, we induced laser ablation using spatiotemporally manipulated double pulses focused from two angles onto a glass surface with a 0.7 ps interval, and captured the images of its dynamics with 5 sequential frames at a frame interval of 0.8 ps. The observed dynamics suggest that the laser profile reflected on the glass surface is influenced by its topography, which in turn affects the behavior of air breakdown plasmas.

Driven two-fluid slow magnetoacoustic waves in the solar chromosphere with a realistic ionisation profile

Context. This study was carried out in the context of chromosphere heating. Aims. This paper aims to discuss the evolution of driven slow magnetoacoustic waves (SMAWs) in the solar chromosphere modelled with a realistic ionisation profile and to consider their potential role in plasma heating and the generation of plasma outflows. Methods. Two-dimensional (2D) numerical simulations of the solar atmosphere are performed using the JOANNA code. The dynamic behaviour of the atmospheric plasma is governed by the two-fluid equations (with ionisation and recombination terms taken into account) for neutrals (hydrogen atoms) and ions (protons)+electrons. The initial atmosphere is described by a hydrostatic equilibrium (HE) supplemented by the Saha equation (SE) and embedded in a fanning magnetic field. This initial equilibrium is perturbed by a monochromatic driver which operates in the chromosphere on the vertical components of the ion and neutral velocities. Results. Our work shows that the HE+SE model results in time-averaged (net) plasma outflows in the top chromosphere, which are larger than their pure HE counterpart. The parametric studies demonstrate that the largest chromosphere temperature rise occurs for smaller wave driving periods. The plasma outflows exhibit the opposite trend, growing with the driver period. Conclusions. We find that the inclusion of the HE+SE plasma background plays a key role in the evolution of SMAWs in the solar atmosphere.

Integration of ML methods with CR model-based optical diagnostic for the estimation of electron temperature in Ga laser produced plasma

Accelerated diagnostic of plasma plays a significant role in controlling and optimizing plasma-mediated processing, particularly for plasma with higher temporal and spatial gradients, such as laser produced plasma (LPP). In the present work, two advanced machine learning (ML) algorithms, random forest regression, and gradient boosting regression are integrated with noninvasive collisional radiative (CR) model-based optical diagnostics to facilitate accurate diagnostics. A comprehensive fine-structure resolved CR model framework is developed by incorporating our consistent cross section data obtained from the Relativistic Distorted Wave method [Suresh et al., “Fully relativistic distorted wave calculations of electron impact excitation of gallium atom: Cross sections relevant for plasma kinetic modelling,” Spectrochim. Acta B: At. Spectrosc. 213, 106860 (2024)]. An extensive dataset of CR model simulated intensities is created to train and test the ML methods. The present CR model is applied to characterize the Gallium LPP coupling with the optical emission spectroscopic measurements of Guo et al. [“Time-resolved spectroscopy analysis of Ga atom in laser induced plasma,” Laser Phys. 19, 1832–1837 (2009)] at different delay times. Further, a detailed correlation study of the line intensity ratios is performed to observe the qualitative behavior of the plasma parameters. The electron temperature results obtained from the CR model, ML, and line ratio methods were compared and found to be in excellent agreement. Overall, the present study demonstrates diagnostic approaches that can benefit the LPP community significantly by providing a rapid understanding of the plasma behavior across various operating conditions.

Low current iodine-fed hollow cathode discharge: insights from fluid model

Abstract As one of the fundamental components, hollow cathodes using noble gas propellant are widely used in electric thrusters. Iodine has become one of the ideal alternative propellants due to its economy and good chemical properties, while due to the complex reactions, characteristics and proper functioning of iodine-fed hollow cathodes are still unknown. Therefore, a model is needed to understand the physical-chemical process of the iodine-fed hollow cathode discharge. In this work, a self-consistent two-dimensional fluid model of the low-current iodine-fed hollow cathode discharge with detailed non-equilibrium plasma chemistry is developed and verified by the voltages of the keeper and anode obtained in the experiments. Simulations show that the electron impact ionization with iodine atoms dominates the discharge process as the density of iodine atoms is much higher than that of iodine molecules due to the electron impact dissociation and thermal dissociation. Moreover, the power balance analysis shows the heating of electrons contributed by the electric field mainly takes place near the keeper and the orifice. Ion current heating contributes significantly to the gas heating compared with the heating by the electron elastic collisions with I and I2 and the heat release or consumption during the neutral reactions. Furthermore, the influence of electronegativity on plasma characteristics is analysed. Simulations involving I− ions bring higher values of ionization degree, discharge power as well as maximum electron and gas temperatures compared with those without I−. This is similar to the differences in the plasma properties between the iodine-fed and xenon-fed hollow cathode to which the low ionization energy, large collision ionization cross-section and the electronegativity of iodine contribute together. In all, these findings can better predict the plasma behaviours in the iodine-fed hollow cathode discharge and may promote the development of the electric propulsion system using iodine propellant.

Toward electron temperature profiles in hot-dense plasmas from x-ray spectral ensembles

High repetition rate laser systems enable new strategies for diagnosing plasma behavior with large datasets. Here, we define an ensemble technique that relies on randomized targeting of x-ray tracer micro-stripes. On each shot, a high-intensity laser pulse is focused on a solid target with Ti tracer stripes embedded in an Al foil, randomly targeting a micro-stripe, a portion of a stripe, or a gap between stripes. High-resolution, time-integrated x-ray spectrometers capture line emission from the portion of the micro-stripe that is heated to sufficiently high electron temperatures. Accumulation of many such cases is used to construct ensemble distributions of x-ray line intensities that encompass all relative offsets of the laser focus to the micro-stripe centers. Synthetic intensity distributions are likewise generated using collisional-radiative modeling. Bayesian fitting of modeled to measured intensity distributions establishes the most likely radial temperature profiles, enabling comparison to hydrodynamic models and calling into question the cylindrical symmetry of these micro-stripe-embedded systems. Ensemble techniques have significant potential for high-energy-density plasma diagnostics, especially with the advent of high repetition rate experiments.

Property of Quark-Gluon Plasma

During the nascent stages of the universe's evolution, matter existed in the form of quarkgluon plasma (QGP), characterized by its presence under conditions of exceedingly high temperature andpressure. Presently, the ability to replicate the QGP state has been attained through relativistic heavy.ion collision experiments, Key indicators of QGP generation encompass the initial collision configurationwhich exerts a discernible infuence on the subsequent momentum and scattering angles of emitted hadronsThis study endeavors to recapitulate the findings of the CMS XeXe collision experiment by meticulouslyscrutinizing data stemming from PbPb collisions at a center-of-mass energy of s = 5.02 TeV. Specificallyour focus centers on an exhaustive analysis of the transverse momentum (pt), azimuthal angle (), ancpseudorapidity () of scattered particles. 'Through this comprehensive approach, we aim to corroborate theimplications drawn from the ClMS XeXe experiment, thereby contributing to a deeper understanding of themechanisms underlying quark-gluon plasma creation and behavior

Surface modification and patterning of polymer thin films by plasma and adsorption behavior of proteins

The surface wettability property of hydrophobic polystyrene (PS) and hydrophilic polyethylene glycol (PEG) thin films subjected to modification by direct current plasma glow discharge is studied. The polymer films exhibited change of surface wettability on exposure to air, nitrogen, oxygen or argon plasmas. In PS films a swift modification to hydrophilic surface and subsequent steady recovery following first order kinetics are observed. The rate of modification and recovery are adjustable by adjusting the plasma ambient and parameters, and additional wet-chemical treatment using ionic solutions. In PEG films the hydrophobic wettability evolve with ageing following the first order kinetics, and is stable for long period on exposure to air ambient. Moreover, a vapor deposition like process is possible using the PEG films as source to deposit self-assembled molecular layers with hydrophobic wettability on other surfaces. Using surface modification or molecular deposition processes, the fabrication of wettability patterns in the surface of PS and PEG films, and on other surfaces by vapor transport using PEG films, and also the possibility to produce gradient wettability patterns are demonstrated. Moreover, the adsorption behavior of immuno-specific system of proteins on surface modified hydrophilic PS films is studied.

Tuning plasma chemistry by various excitation mechanisms for the H2O2 production of atmospheric pressure plasma jets

Abstract Atmospheric pressure plasmas (APPJs) are widely used for research purposes or industrial applications. There are plenty of different APPJs designed with various geometries and excitation frequencies ranging from kHz over RF (MHz) to fast ns pulses. A direct comparison of these APPJs is often challenging as the different geometries or the different excitation frequencies are not the same and can strongly influence plasma behaviour. In this work, this challenge is met and overcome by the use of an APPJ which can be operated at various excitation frequencies. kHz pulsing with a high voltage peak with µs rise time, sinusoidal voltage pulse at 13.56 MHz and fast high voltage ns pulse were applied to the plasma jet used. The production of H 2 O 2 was investigated by treating liquids and measuring the H 2 O 2 concentration in the treated liquid. Fast ns pulses and RF excitation show similar results, while the kHz excitation is less effective in the H 2 O 2 production.

Investigate of thermodynamic behavior of magnetized two-flavor quark-gluon plasma

In this paper, we extend the self-consistent quasi-particle model proposed by Zong et al. [Phys. Lett. B 711, 65 (2012)] to the case of finite magnetic field. The vacuum infinity zero-point energy is successfully eliminated by introducing a classical thermo-magnetic background field [Formula: see text] in the effective Lagrangian based on Zong’s method. By considering relativistic Landau energy levels, we have applied the improved quasi-particle model to the case of a two-flavor quark gluon plasma. We obtain a finite partition function and calculate the energy density, pressure and entropy density at zero chemical potential. These results are qualitatively consistent with the results of previous literature works.

Simulation of Interaction Between Proton‐Electron Plasma Beam and Arched Magnetic Field

ABSTRACTThe present study investigates the interaction between a proton‐electron plasma beam and an arched magnetic trap using the particle‐in‐cell (PIC) simulation method. The results show that when the magnetic field is sufficiently weak, the beam disrupts the arched magnetic field configuration, causing the breaking and reconnection of magnetic field lines. The relationships between the coil current threshold (the coil current at which the disruption of the magnetic induction just happens) and initial plasma velocity, and between the critical beam velocity (the plasma is just enough to reach the arched magnetic field) and coil current, are quantified. Additionally, the interaction between the beam and the arched magnetic field is observed to induce microwave excitation. These findings lay the foundation for theoretically simulating the dynamic behavior of space plasma in a unique magnetic field environment within a laboratory setting.

Influence of electrode transparency on the plasma properties of a cylindrical IEC plasma source

This study investigates the influence of cathode and anode grid transparency on the plasma properties of a Cylindrical Inertial Electrostatic Confinement plasma source. The primary focus is to elucidate how variations in the transparency of the electrodes impact plasma characteristics and the operational performance of the source, particularly during spray jet mode. Employing optical emission spectroscopy (OES) and Langmuir probe diagnostics, the plasma behavior is analyzed comprehensively. The results demonstrate that cathode transparency has a pronounced effect on discharge current and plasma density within the cathode. Conversely, the transparency of the anode has only a little influence the ignition characteristics and operational stability of the plasma source. The findings highlight the importance of utilizing cathode transparency to adjust both the pressure and voltage operating ranges of the IEC source in spray jet mode, optimizing its performance for various applications.

Spectral behavior and expansion dynamics of Gd plasma generated by dual-pulse laser irradiation.

Laser-produced gadolinium plasma (Gd-LPP) emerges as a promising candidate for next-generation nanolithography light sources. In this study, a dual laser pulse scheme was implemented to achieve a narrow spectral peak. By varying the pre-main pulse delay and pre-pulse laser energy, optimal conditions of 40 ns delay and 50 mJ energy were identified to improve spectral purity. Radiation hydrodynamics simulations revealed that the improved spectral purity stems from a flatter density gradient at the ablation front and a lower average electron density in the EUV emission region. Additionally, reheating the pre-formed plasma with a short main pulse mitigated plasma squeezing, resulting in an even lower electron density and thus improved spectral purity. Our findings suggest that spectral narrowing in the dual-pulse scheme, essential for better matching with multilayer reflection bandwidths, can be optimized through precise control of pre-pulse energy, pre-main delay, and main-pulse duration.

Distinct polytropic behavior of plasma during ICME-HSS interaction

Interplanetary Coronal Mass Ejections (ICMEs) and High-Speed Streams (HSSs) are significant drivers of space disturbance in interplanetary space. The interaction between these structures can lead to various phenomena, including the generation of waves, enhanced geo-effectiveness, particle acceleration, and more. However, understanding the plasma thermodynamic properties during an ICME-HSS interaction remains an open problem. In this study, we utilize observations from STEREO and WIND to investigate the thermodynamic behavior of plasma within an ICME and a HSS. Here, we used the thermal pressure (Pth) and proton number density (Np) data from spacecraft. By fitting the linear model to the scattered data of lnPth vs lnNp we estimated the polytropic index (α). Our analysis reveals that the ICME observed before its interaction with the HSS by STEREO-A exhibits a polytropic index α∼1.0, indicating an isothermal process. Conversely, WIND observations of the same ICME before its interaction with the HSS show a nearly isothermal behavior, with α=0.7. The HSS observed by WIND demonstrates α=1.8 before its interaction with the ICME. Further analysis of WIND observations within the ICME-HSS interaction region determines a polytropic index of α=2.5. These findings suggest that the HSS region displays a nearly adiabatic behavior, the ICME region manifests closely isothermal characteristics, and the ICME-HSS interaction region exhibits super-adiabatic behavior. We propose that the expansion of ICME increases due to its propagation in the vicinity of HSS, potentially leading to additional cooling of the observed ICME magnetic cloud, which differs from the ambient solar wind.

A coupled plasma-thermal model for hollow cathode power decomposition and parametric analysis

Abstract A 2D axisymmetric transient coupled plasma-thermal model is developed to simulate the plasma behavior during the self-sustained discharge of hollow cathodes, which presents a complete hollow cathode structure and energy transfer processes in multiphysics fields. The model has been validated by quantitative agreement between the simulation results and experimental data on the plasma and emitter temperature at the NSTAR cathode. The effects of thermal protection design, operating conditions, and geometric design on the cathode performance are analysed through electric and thermal power decomposition. The parametric analysis shows that the optimal thermal protection design is to use a 1/3 thickness cathode tube with 4 layers of radiation shielding close to the tube, which reduces 43.7% conductive and 61.1% radiative heat dissipation, respectively. Increasing the inlet flow rate counter-intuitively reduces the emitter temperature due to the potential reversal in the diffusion electric field dominated region, revealing that the flow rate can be traded for the dual optimisation of lifetime and power consumption. Under high current conditions, the IAT effect dominates the plume resistance to increase the discharge voltage after an inflexion point, which is the main factor limiting the cathode performance. A large internal radius gives a uniform low emission and helps to prolong life, while the orifice length should be avoided to be longer than 4 times the orifice radius due to the significantly enhanced Joule heating in the narrow orifice. The orifice radius determines the power deposition due to electron and ion bombardment through potential penetration. For high-current discharger cathodes dominated by electron bombardment, large or through-orifice designs are preferred, while for low-current neutralizer cathodes dominated by electron bombardment, small-orifice designs are recommended.