High-temperature Plasma Research Articles

Microstructure and high-temperature tribological behaviours of nano-HfC reinforced Inconel 625 composite coating by plasma-transferred arc welding

The study involved plasma arc transfer welding (PTAW) for preparing coatings of Inconel 625 alloys that contained different amounts of nano-sized hafnium carbide (nano-HfC) particles. The impact of nano-HfC on the microstructure evolution and mechanical properties of PTAWed Inconel 625 were investigated. The research reveals that nano-HfC decomposes during the high-temperature plasma arc process and then react with O element to generate nano-HfO2. These HfO2 can serve as nucleation sites for MC carbides, which restricts the growth of secondary dendrite arms, leading to a more disordered grain growth direction. Simultaneously, the decomposition of HfC can increase the C/Nb ratio of the matrix, effectively suppressing Laves phase formation while encouraging the development of MC carbides. Compared with IN625, the wear rate of composites at room temperature and 600 °C were decreased. Notably, at 600 °C, the wear rate of the coating with 0.5 wt% HfC is the lowest among all the samples, as reflected by a noteworthy reduction in wear rate of 50 %. This is mainly attributed to the refinement of γ matrix, reduction of Laves phase as well as precipitation of the fine-sized MC carbides. This work illustrates that adding nano-HfC is an effective way to improve the wear resistance of the PTAWed Inconel 625.

An Experimental Investigation On The Effect Of Laser Energy Deposition In An Over-Expanded Jet

The shock train structure of a supersonic over-expanded jet is the product of the interaction between the jet flow at the nozzle exit and the ambient environment. Although the effect of flow disturbances on the performance of the supersonic inlets has been studied in detail, a limited understanding of the shock train dynamics subject to flow disturbances is available for over-expanded jets. This experimental investigation focuses on understanding the influence of perturbations due to short-duration energy deposition on the shock train structure and its dynamics in an axisymmetric over-expanded Mach 2.52 jet. The flow is perturbed by laser-induced breakdown, creating a shock wave and a high-temperature plasma zone in the shock train. A high-speed self-aligning focusing schlieren system is used to visualize the flow structure variations by measuring the shock angles and Mach disk height and width to characterize the shock train dynamics and the flow structure recovery process. The response of jet flow to the perturbation at the nozzle exit and the pre-reflection point is found to be similar, however, the response of the supersonic jet to the post-reflection energy deposition is significantly different. The damping ratio for the pre-reflection point and nozzle exit cases found are nearly constant for all scenarios whereas it is linearly dependent on the jet chamber pressure for the post-reflection cases. The frequency of the oscillations is found to be the same for all cases and irrespective of the chamber pressure, laser energy, and deposition location, approximately 10 kHz. The transition from Mach to regular reflection and vice versa are observed at a chamber pressure of Pc = 689 kPa. Any perturbation to the shock structure of a supersonic over-expanding jet at close to the steady-state bifurcation condition between Mach and regular reflection will exhibit Mach-to-regular transition or vice versa.

Plasma pressure profiles in a sheared-flow-stabilized Z-pinch

We report the plasma pressure reached inside the central plasma column of a sheared-flow-stabilized Z-pinch using Thomson scattering measurements. Building on previously reported experimental results and the analysis methods established for the high temperature and moderate density plasmas generated on the FuZE device, we show evidence of a central plasma region with higher electron temperature and density, which is consistent with a pinch behavior. Elevated electron temperatures up to 2.25 ± 0.8 keV and densities up to (4.9±0.2)×1017 cm−3 are observed to temporally coincide with the fusion neutron production from the plasma. Reconstructed plasma pressure profiles highlight the presence of a several millimeter-wide column with elevated pressure whose location varies shot-to-shot. The plasma pressure rises as neutron production from the deuterium plasma increases, reaching a peak value of 2.6 kBar. This peak value is consistent with a radially force-balanced pinch equilibrium model based on the measured ∼320 kA pinch current. Complete datasets were obtained at two axial locations, 10 and 20 cm axial position from the tip of the central electrode, which corroborate the estimated neutron source axial lengths.

Unravelling instrumental mass fractionation of MC-ICP-MS using neodymium isotopes

Since the initial discovery of the non-exponential mass fractionation (non-EMF) of Nd isotopes analysis in 2002, similar deviations from an EMF pattern have been reported for measurements of a number of isotope systems (e.g., Si, Ge, Sr, Sn, Ba, Yb, W, Os, Hg and Pb) with MC-ICP-MS. However, the previous controversial reports on the magnitude of the deviations from EMF suggest that instrumental mass bias behaviour of MC-ICP-MS is neither fully understood nor well-characterised. Consequently, the standard approach of using a mass dependent fractionation (MDF) correction model (e.g., exponential law) may lead to both inaccurate and imprecise results. In this study, we systematically characterise the instrumental mass fractionation of MC-ICP-MS using Nd isotope measurements carried out under different plasma conditions, quantified using the normalised argon index (NAI) as an estimate of plasma temperature. Our results indicate that the mass bias of MC-ICP-MS is not always a simple exponential function of mass but shows systematic deviations from an EMF behaviour, which are closely associated with decreased NAIs. As a result, the conventional exponential correction yields a 143Nd/144Nd value of 0.512257 for the reference material BHVO-2 when the NAI is low, which is 722 ppm lower than the reported value of 0.512979. By tuning the plasma to higher NAIs (higher plasma temperatures), the deviations from the EMF array are systematically attenuated and the exponential correction is able to correct for the instrumental mass bias under high NAIs. In contrast, a regression correction model for Nd isotopes is developed to account for the observed mass fractionation behaviour that does not follow EMF under low NAIs, given that the regression correction relies on the observed loglinear fractionation of different isotope pairs and does not require both isotope ratios to undergo EMF. We expect that the analytical protocol and fundamental insights gained in this study are applicable to a wide range of other isotope measurements with MC-ICP-MS.

Sphaleron damping and effects on vector and axial charge transport in high-temperature QCD plasmas

We modify the anomalous hydrodynamic equations of motion to account for dissipative effects due to quantum chromodynamic (QCD) sphaleron transitions. By investigating the linearized hydrodynamic equations, we show that sphaleron transitions lead to nontrivial effects on vector and axial charge transport phenomena in the presence of a magnetic field. Due to the dissipative effects of sphaleron transitions, a wave number threshold kCMW emerges characterizing the onset of chiral magnetic waves. Sphaleron damping also significantly impacts the time evolution of both axial and vector charge perturbations in a QCD plasma in the presence of a magnetic field. Based on our analysis of the linearized hydrodynamic equations, we also investigate the dependence of the vector charge separation on the sphaleron transition rate, which may have implications for the experimental search for the chiral magnetic effect in heavy ion collisions. Published by the American Physical Society 2024

On the Coefficient of Nonlinear Coupling of Two Electromagnetic Waves with Ordinary Polarization and a Longitudinal Upper Hybrid Wave in a High-Temperature Plasma

On the Coefficient of Nonlinear Coupling of Two Electromagnetic Waves with Ordinary Polarization and a Longitudinal Upper Hybrid Wave in a High-Temperature Plasma

64‐4: ECR Plasma Source for Copper Thin Film Dry Etching

Dry etching process of thin copper films using high electron temperature ECR (electron cyclotron resonance) plasma source is developed. With ECR source and RIE (reactive ion etching) mode, etching rate of 175 nm/min is achieved. Dry etching is performed under high electron temperature plasma source with low temperature substrate and employing a reactive ion etching mode. To compensate the large area etching uniformity, scanning low temperature susceptor is adopted. Rectangular‐type microwave slot antenna (ReSLAN) is used to generate ECR plasma.

High resolution X-ray spectra of the time evolution of emission from metastable electronic states of highly charged Ni-like ions

Metastable levels of highly charged ions that can only decay via highly forbidden transitions can have a significant effect on the properties of high temperature plasmas. For example, the highly forbidden 3d10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{10}$$\\end{document}J=0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{J=0}$$\\end{document} - 3d9\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^9$$\\end{document}4 s (52,12)J=3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(\\frac{5}{2},\\frac{1}{2})_{J=3}$$\\end{document} magnetic octupole (M3) transition in nickel-like ions can result in a large metastable population of its upper level which can then be ionized by electrons of energies below the ground state ionization potential. We present a method to study metastable electronic states in highly charged ions that decay by x-ray emission in electron beam ion traps (EBIT). The time evolution of the emission intensity can be used to study the parameters of ionization balance dynamics and the lifetime of metastable states. The temporal and energy resolution of a new transition-edge sensor microcalorimeter array enables these studies at the National Institute of Standards and Technology EBIT.Graphical abstractNOMAD calculated time evolution of the ratio of the Ni-like and Co-like lines in Nd at varying electron densities compared with measured ratios

Optimization of pellet design parameters to achieve deep fueling depth in EAST plasma with PAM code

Deep pellet fueling depth is necessary to achieve a high-density high confinement operation and to conduct some pellet-related researches in current devices, such as trigger of internal transport barrier, and to achieve high fusion power and tritium burn-up fraction in future fusion devices. The newly developed PAM code which can make a fast evaluation on pellet ablation and deposition is applied to optimize injection parameters to achieve deep pellet fueling. Systematic scans on pellet injection parameters including pellet injection positions, injection angles, sizes and speeds are performed for optimization purpose, while at the same time demonstrating flexibility and time efficiency of the PAM code. Dependences of the pellet fueling depth on these injection parameters are revealed by simulation results and analyzed. Simulation results indicate that pellet penetration contributes more to the deep pellet deposition than the ∇B -induced plasmoid drifts in low temperature plasmas, while deep pellet fueling in reactor relevant high temperature plasmas has to rely on plasmoid drifts. Though a shallow penetration is expected in high temperature plasmas, the ∇B -induced plasmoid drift is expected to be larger than that in relatively low temperature plasmas.

Hamiltonian formalism for Bose excitations in a plasma with a non-Abelian interaction I: Plasmon – hard particle scattering

Hamiltonian theory for collective longitudinally polarized gluon excitations (plasmons) interacting with classical high-energy test color-charged particle propagating through a high-temperature gluon plasma is developed. A generalization of the Lie-Poisson bracket to the case of a continuous medium involving bosonic normal field variable ak⁎a and a non-Abelian color charge Qa is performed and the corresponding Hamilton equations are presented. The canonical transformations including simultaneously both bosonic degrees of freedom of the soft collective excitations and degree of freedom of hard test particle connecting with its color charge in the hot gluon plasma are written out. A complete system of the canonicity conditions for these transformations is derived. The notion of the plasmon number density Nkaa1′, which is a nontrivial matrix in the color space, is introduced. An explicit form of the effective fourth-order Hamiltonian describing the elastic scattering of a plasmon off a hard color particle is found and the self-consistent system of Boltzmann-type kinetic equations taking into account the time evolution of the mean value of the color charge of the hard particle is obtained. On the basis of these equations, a model problem of the interaction of two infinitely narrow wave packets is considered. A system of nonlinear first-order ordinary differential equations defining the dynamics of the interaction of the colorless Nkl and color Wkl components of the plasmon number density is derived. The problem of determining the third- and fourth-order coefficient functions entering into the canonical transformations of the original bosonic variable ak⁎a and color charge Qa is discussed. With the help of the coefficient functions obtained, a complete effective amplitude of the elastic scattering of plasmon off hard test particle is written out.

Exploring of two connection forms of the tungsten tile and CuCrZr heat sink for first wall mockup

The first wall (FW) of a blanket or divertor faces high temperature plasma. Thus, the FW needs to withstand extremely high heat fluxes. Periodic plasma pulses bring some reliability challenges to FW structures. The FW is composed of tiles, heat sink and a bolt with different connection between the tile and the heat sink. In this study, the performances of two connection forms for the tile and the heat sink were investigated. The FLUENT software was used to evaluate the heat transfer performances for the two types structure. Elastic-plastic analysis was subsequently adopted to estimate the structural properties based on the thermal hydraulic results. At the same time, the thermal and structural results under a transient high thermal load (2 MW/m2) were also analyzed. Finally, structural fatigue analysis under a cyclic thermal load with 0.5 MW/m2 was also performed. The results indicated that there was a large discrepancy in the tile results for the two connections, while the differences in the heat sink result were not significant. The advantages and disadvantages of two connections also be discussed at last.

Optimizing the electromagnetic wave absorption properties of core-shell Fe/FeN/Fe3C@GN nanoparticles by low-temperature NH3 plasma

Surface modification via low-temperature plasma has an extensive application prospect in different engineering fields due to its comprehensive merits in facilitating the introduction of functional groups and creating more heterogeneous interfaces. Herein, a simple high-temperature plasma method is developed to get novel multiple-phase nanocomposites of core-shell Fe/FeN/Fe3C@GN nanoparticles with bifunctional characteristics of microwave absorption (MA) and anti-corrosion. And then, we further investigate the MA properties of Fe/FeN/Fe3C@GN nanoparticles after low-temperature NH3 plasma etching. It is found that surface modification of Fe/FeN/Fe3C@GN nanoparticles can generate remarkable changes in specific surface areas, Raman features and MA properties of these nanocomposites. The Fe/FeN/Fe3C@GN nanoparticles after NH3 plasma etching possess excellent MA properties with an optimal reflection loss (RL) of −51.0 dB at an ultra-thin thickness of 1.9 mm with a low filling content of 30 wt% and the corresponding effective absorption bandwidth (EAB < −10 dB) up to 4.7 GHz (13.3–18.0 GHz). The fascinating MA properties of etched Fe/FeN/Fe3C@GN nanoparticles may be attributed to the cooperative effect of several points: (i) The NH3 plasma etch introduces a large number of polar functional groups, which can be regarded as the polarization center to produce more polarization loss; (ii) The appropriate dielectric loss and impedance matching achieve a good balance, and the abundant heterogeneous interface significantly enhances the polarization relaxation loss; (iii) The existence of hetero-nanostructure further improves the multiple reflections and scattering of the propagating microwaves. In addition, this work provides a new strategy for the design and fabrication of core-shell MA materials.

High temperature negative mass plasma

A review of studies of matter with negative mass - negamatter, consisting of negaparticles - is given. Based on the assumption that Newton's laws are valid for negaparticles, their behavior in relation to other particles is described. It has been discovered that high-temperature plasma is a negasubstance, but only such a plasma whose temperature is above a certain critical temperature, depending on the chemical composition of the original substance, can be calculated using the appropriate formula. In addition, if anybody is in a state of motion with a speed above 235696.8871 km/s, then its substance undergoes a phase transition and becomes negamatter.

Collapse characteristics and deposition behaviour of PS–PVD powders with different crushing strengths

Plasma spray–physical vapour deposition uses finely agglomerated spherical powders as raw materials; these powders undergo a complex process of dispersing–melting–evaporation–condensation in high-temperature and high-speed plasma jets to attain the desired physical phase and high-performance columnar-like structure thermal barrier coatings. Currently, the interactions between the powders and the jets have not been fully disclosed. The article examines the crushing strength of powders with various particle sizes and properties. To further elaborate the crushing process, discrete element simulation was used. Additionally, powder spray deposition experiments were conducted to disclose the association between powder properties and the efficiency of coating deposition. The findings indicate that the stiffness of the powder and the size of the internal particles have an impact on the crushing strength of the powder. The stronger the bond strength caused by greater powder stiffness, the more effective the dispersion effect becomes. Furthermore, the smaller the particle size, the higher the compressive and collapse strength. Therefore, the greater the crushing strength of the powder, the higher the rate of powder deposition.

Физика залечивания нанопор в конденсированном веществе в условиях воздействия лазерного излучения и высокотемпературной плазмы

The paper theoretically and experimentally investigates the influence of laser radiation and high-temperature plasma on changes in the physical properties of amorphous-nanocrystalline materials with nanopores in a thin surface layer. At present, the possibility of simultaneous increase of hardness and resistance to cracking of the material surface because of selective laser action has been experimentally established. Experimental results can be explained based on the model of selective impact of laser radiation on individual nanopores. The physics of laser selective initiation of healing processes of inhomogeneous/defective areas at the nanoscale has been investigated. Using the proposed physical model, the specificity of selective heating of areas near nanopores, as well as the influence of nanoscale defects in the structure on the specificity of isotherm propagation has also been revealed. The process of healing of nanopores located in the inhomogeneously heated surface layer of the material under the action of shock loading is considered. Theoretical results are compared with experimental data. It is shown that as a result of selective laser treatment it is possible to increase microhardness by three-four times, with simultaneous growth of resistance to cracking under conditions of local loading by the Vickers pyramid. The results obtained can be explained within the framework of ideas about selective laser healing of nano- and micro-sized defects located in the surface layer of the material. Thus, the physical and mechanical properties of the surface of condensed materials in an extreme state caused by strong compression under conditions of simultaneous short-term heating to high temperatures have been studied theoretically and experimentally.

A control oriented strategy of disruption prediction to avoid the configuration collapse of tokamak reactors

The objective of thermonuclear fusion consists of producing electricity from the coalescence of light nuclei in high temperature plasmas. The most promising route to fusion envisages the confinement of such plasmas with magnetic fields, whose most studied configuration is the tokamak. Disruptions are catastrophic collapses affecting all tokamak devices and one of the main potential showstoppers on the route to a commercial reactor. In this work we report how, deploying innovative analysis methods on thousands of JET experiments covering the isotopic compositions from hydrogen to full tritium and including the major D-T campaign, the nature of the various forms of collapse is investigated in all phases of the discharges. An original approach to proximity detection has been developed, which allows determining both the probability of and the time interval remaining before an incoming disruption, with adaptive, from scratch, real time compatible techniques. The results indicate that physics based prediction and control tools can be developed, to deploy realistic strategies of disruption avoidance and prevention, meeting the requirements of the next generation of devices.

Enhanced surface passivation of GaAs nanostructures via an optimized SiO2 sol-gel shell growth

Gallium arsenide (GaAs) is an important compound semiconductor for optoelectronic devices. However, the fast nonradiative recombination velocity of GaAs requires surface passivation for the nano-optoelectronic and nanophotonic applications. Despite strides have been made in GaAs surface passivation, chemical treatments like sulfidation and nitridation suffer from reproducibility and stability issues, thus requiring protective layer encapsulation. Traditional vacuum based film passivation exposes samples to high temperature plasma, causing surface damage, and is expensive. Here, we demonstrate an effective passivation method via sol-gel growth of SiO2 shell on both dry etched GaAs nanopillar and bottom-up grown GaAs nanowires at room temperature with uniform coating and controlled thickness from sub-10 nm to around 100 nm, showing advantages in low cost as well as suitability for different types of nano morphology. X-ray photoelectron spectroscopy analysis confirms that the SiO2 sol-gel method with the addition of (NH4)2S can significantly remove the native oxides on the surface. Under the optimized SiO2 coating procedure, the emission intensity of dry etched GaAs nanopillar with a diameter of 0.5 μm is enhanced about 29.6 times and the decay lifetime of the minority carriers with a diameter of 1.8 μm increased from 43.6 to 477.5 ps. Thus, the easy fabrication, broad suitability, as well as effective passivation effect turn sol-gel growth of SiO2 into a cost-effective surface passivation approach for III–V nanostructures.

Extreme environmental micro-plasma electrolyte oxidation induced defect-rich Au nanoparticles catalyst improving the nitrophenol hydrogenation reaction

The defect-rich Au nanoparticles (NPs) catalyst on Mg surface was prepared by the micro-plasma electrolyte oxidation (MPEO) utilizing liquid nitrogen as the cooling medium. MPEO is a high-temperature plasma oxidation process that decomposes the [AuCl4]-precursor salt to form metastable state Au NPs. The rapid quenching effect of liquid nitrogen occurs during this non-equilibrium process and generates numerous defects on the Au NPs, thereby altering their electronic state. Consequently, the catalytic performance of this Au/MgO catalyst was outstanding, exceeding that of the sample prepared without using liquid nitrogen. This finding indicates that the harsh environment plays a crucial role in producing defect-rich Au NPs and improving the catalytic efficiency.

C/C-HfC-SiC composites with simultaneous the resistance to ultra-high temperature airflow erosion and high temperature oxidation

HfC-SiC modified C/C composites containing in situ formed Si-HfC-HfSi2 ablation resistant layer and SiC oxidation resistant layer were successfully prepared by reactive melt infiltration (RMI) combined with gaseous silicon infiltration (GSI). A comparative study was conducted on the anti-oxidation and anti-ablation performance of the C/C-HfC-SiC composites with GSI (noted as RG-CHS) and without GSI (noted as R-CHS). After oxidation at 1,500 °C for 200 min, the oxide film of RG-CHS remained intact. The mass and linear ablation rates decreased from 1.31 mg/s and 7.36 μm/s to 0.12 mg/s and −0.22 μm/s after GSI process, respectively. The introduction of low melting point phases and reducing surface defects can improve the high temperature oxidation resistance and plasma ablation resistance of the composites.

Enhanced high temperature ablation resistance of dense ZrB2–Al2TiO5 composite coating by very low-pressure plasma spraying

ZrB2-based composite coatings with addition of Al2TiO5 were prepared via very low-pressure plasma spraying using mechanically mixed powder of ZrB2 and Al2O3-40 wt%TiO2 (AT40). The ablation behavior of the composite coating was investigated using a high temperature plasma jet at a temperature of ∼2500oC. Results demonstrate the addition of AT40 improved the ablation resistance of the ZrB2 coatings at high temperatures. The coating with 17 vol%AT40 addition exhibited the lowest ablation rate, approximately 1.33 μm/s, which is only one-third of that of the pure ZrB2 coating. The added AT40 filled the pores between ZrO2 crystals during ablation, reducing oxygen penetration and lowering the ablation rate. However, excessive addition of AT40 hindered gaseous B2O3 release and thus led to large pore formation, impairing the protective effect. The ZrB2-AT40 coating is a promising candidate for high-temperature applications.