Plasma Behavior Research Articles

Impurity Behavior in High Performance ADITYA Tokamak Plasmas

Impurity Behavior in High Performance ADITYA Tokamak Plasmas

Study of self‐organised criticality in a coaxial plasma source with gridded cathode

AbstractMultiple luminous sheath structures develop in the localised plasma formation inside a cylindrical gridded cathode plasma source. These structures gradually expand into the whole vessel and undergo a critical state through self‐organised criticality (SOC) along with pronounced sheath oscillations during the variation of anode potential. The present investigation emphasises the stability properties associated with the oscillations of the sheath potential structures in the cylindrical‐gridded cathode in glow discharge regime through SOC phenomena through non‐linear time series analysis. The non‐linear temporal and spatial analysis of potential structure and dynamics of charged particles are correlated with SOC in cylindrical‐gridded cathode in glow discharge regime through the dynamics of multiple sheath structure formations. The existence of flicker noise and long‐range correlation in the time series suggests the existence of SOC behaviour in the system, the multiple sheath structures evolve through reduction and addition of layers. Cylindrical‐gridded cathode discharge initiation during formations of multiple sheath structures, switching of discharge regimes with anode potential, layer reduction and addition inside the sheath structures through SOC behaviour, renders uniqueness to the present regime of investigation. Self‐organised pattern formations and self‐organised criticality behaviour investigated in the present glow discharge regime using the cylindrical‐gridded cathode source are of prime importance to understand the complex behaviour of plasmas in the field of hollow cathode discharges.

A generalised formulation of G-continuous Bezier elements applied to non-linear MHD simulations

The international tokamak ITER is progressing towards assembly completion and first-plasma operation, which will be a physics and engineering challenge for the fusion community. In the preparation for ITER experimental scenarios, non-linear MHD simulations are playing an essential role to actively understand and predict the behaviour and stability of tokamak plasmas in future fusion power plant. The development of MHD codes like JOREK is a key aspect of this research effort, and provides invaluable insight into the plasma stability and the control of global and localised plasma events, like Edge-Localised-Mode and disruptions. In this paper, we present an operational implementation of a new, generalised formulation of Bezier finite-elements applied to the JOREK code, a significant advancement from the previously G1-continuous bi-cubic Bezier elements. This new mathematical method enables any polynomial order of Bezier elements, with a guarantee of G-continuity at the level of (n−1)/2, for any odd n, where n is the order of the Bezier polynomials. The generalised method is defined, and a rigorous mathematical proof is provided for the G-continuity requirement. Key details on the code implementation are mentioned, together with a suite of tests to demonstrate the mathematical reliability of the finite-element method, as well as the practical usability for typical non-linear tokamak MHD simulations. A demonstration for a state-of-the-art simulation of an Edge-Localised-Mode instability in the future ITER tokamak, with realistic grid geometry, finalises the study.

High temperature oxidation behavior of atmosphere plasma sprayed AlCoCrFeNi high-entropy alloy coatings

In this work, AlCoCrFeNi high-entropy alloy (HEA) coating was prepared by atmosphere plasma spraying (APS) and the oxidation behavior at 800, 900, 1000 °C was studied. A new passivation mechanism based on element migration and oxidation process was proposed. Results showed that the weight gain curve of HEA coating was a two-stage parabola. The steady-state oxidation of Al was dominant at all temperatures within 50 h. Al migrated laterally and longitudinally to form a dense Al2O3 passivation layer with mesh structure, which effectively prevents the internal diffusion of O. High temperature induced BCC to FCC phase transformation of HEA alloy thus resulted in the formation of Fe-Ni-rich spinel oxides. The proposed mechanism indicated that increasing Al content in AlCoCrFeNi coating would improve its oxidation-resistance.

Compressive deformation behaviour and toughening mechanisms of spark plasma sintered NiAl-CNT composites

Carbon nanotube (CNT)-reinforced NiAl intermetallic composites were produced via powder metallurgy, particularly spark plasma sintering. The aim of this study was to evaluate the room temperature compressive behaviour of the sintered NiAl-CNT composites with a focus on the toughening mechanisms of the CNT reinforcement and the resulting microstructures. Remarkably, the NiAl-0.5 wt% CNT composites exhibited a balanced combination of strength and toughness despite a trade-off tendency, due to the presence of both coarse and fine bimodal grains in its microstructure. Mechanical properties of 831 MPa, 429 MPa and 360 HV were recorded for the ultimate compressive strength (UCS), compressive yield strength (CYS) and microhardness of the NiAl-0.5%CNT intermetallic composites, respectively, along with a compressive strain of 12% being higher than the unreinforced NiAl.

Dual-pulse laser deposition offers greater control over plasma plumes

Examining the effects of a second laser pulse on plasma energy, duration, and behavior

A semi‐relativistic time‐fractional Vlasov–Maxwell code for numerical simulation based on circular polarization and Landau damping instability

AbstractThe Vlasov–Maxwell system is a revolutionary tool to model and analyze the dynamic behavior of the collisionless plasma in the existence of the electromagnetic field. In this perspective, the investigation of this system with the concept of the time‐fractional derivative is the new benchmark and also one of the main objectives of this article. In order to construct the numerical solution, we propose and implement a novel scheme which grounded on finite‐difference and spectral approximations. The temporal variable is tackled by using finite‐difference approximation, whereas spatial variables approximated via sifted Gegenbauer polynomials. Various simulations are performed to explore new phenomena and demonstrate the accuracy and reliability of the proposed method. Convergence and error bound of the suggested methods are investigated theoretically, whereas stability analysis performed numerically. Moreover, the developed method can be used conveniently to examine the numerical solution of other multidimensional highly nonlinear fractional or variable order problems of physical nature.

Two-component plasma and electron trapping’s influence on the potential of a solitary electrostatic wave with the dust-ion-acoustic speed

In this paper, the ion-acoustic waves’ dynamic behavior in plasma and dusty plasma is investigated to explain the electron trapping’s effect on the potential of a solitary electrostatic wave with the dust-ion-acoustic speed in two-components plasma. This study investigates the soliton wave solutions of the Schamel–Korteweg–de Vries (S–KdV) equation that Hans Schamel derived in 1973. In a nonlinear dispersive medium, the S–KdV equation is used to describe a coherent localized wave structure propagates are demonstrated. One-dimensional, unmagnetized plasma with positive ions, negative ions, trapped electrons, and stationary dust grains with both positive and negative charges is studied for the nonlinear propagation of dust-ion-acoustic (DIA) waves. The Bernoulli sub-equation function (BSEF) method is applied to the S–KdV equation for constructing some novel soliton wave solutions that explain the effect of the plasma parameters on the DIA solitary waves. The obtained solitary wave solutions are represented through some different graphs by Mathematica 12 software. Additionally, the axisymmetric pulse propagation is demonstrated in some stream plots. All the obtained solutions are checked by putting them back into the original model.

Analysis of E × B Drifts in Earth's Magnetosphere During Geomagnetic Reversals: Potential Consequences for Plasmasphere Behavior and Stability

AbstractGeomagnetic pole reversals occur frequently throughout geologic history, although one has not yet occurred in recorded time. Magnetohydrodynamic models of Earth's core have revealed that during a reversal, the magnetic dipole moment disappears, leaving higher‐order moments. Previous research examined quadrupole magnetic field topologies and quantitatively specified the magnetic equators of those topologies but did not fully examine charged particle drift motion and stability in the inner magnetosphere. Earth's closed magnetosphere is primarily dominated by two electric fields, the corotational and convection generated electric fields. drifts from these fields ultimately drives the behavior of the cold plasma of the plasmasphere. In a quadrupole‐dominated magnetic field, the plasma motion generated by the drifts would be dramatically different from the classical dipole field plasma convection. Three quadrupole topologies were evaluated, and the drift was analyzed along the magnetic equators of these topologies to characterize and quantify the resultant plasma motion and evaluate the behavior, structure and stability of the plasmasphere. We also tested for plasmaspause and magnetopause boundary sensitivity to magnetic field strength. The direction of the convection flow is hemispherically dependent for the η = 0 and 0.5 quadrupole topologies, that is, the plasma in the Northern Hemisphere convects tailward, and the Southern Hemisphere convects sunward. The η = 1 topology demonstrates evidence of strong plasmasphere erosion due to the intersection of the magnetic equators, and the magnetopause and plasmapause of the η = 1 topology are particularly sensitive to reductions in magnetic field strength.

Design of the cross-polarization scattering diagnostic on the HL-2A tokamak

A new cross-polarization scattering (CPS) diagnostic has been developed on HL-2A, which aims to measure the local magnetic fluctuation inside the plasma. It is based on the scattering of an incident microwave beam into the perpendicular polarization by magnetic fluctuations. The CPS diagnostic has been designed in the Q-band (33–50 GHz), which consists of the electronic system, quasi-optical, and polarization rejector. The ray-tracing code is used to simulate the propagation of the probe and scattered rays. To test the performance of the quasi-optical system, a 3D test platform is built and detailed test results are shown. Two methods are developed for polarization rejector on HL-2A: wire grid polarizer and dual-polarized horn antenna (DPHA). The laboratory test result shows that the polarization rejection of both methods is better than 30 dB, which meets the needs for magnetic fluctuation detection. In the future, the CPS diagnosis will be used to study the electromagnetic turbulence behavior in the high-performance plasma of the HL-2A tokamak.

Particle-in-Cell Investigation on Temporal Flow and Expansion Behaviors of Deuterium-Titanium Plasmas From Ion Source to Expansion Cup

By using a self-programed circular cylindrical coordinates 2-D, three velocity component, particle-in-cell (2D3V-PIC) code, the temporal dynamic flow and expansion behaviors of deuterium–titanium plasmas from the ion source to expansion cup are numerically studied in this article. The simulation results demonstrate as follows. There is a notable plasma sheath near the wall of the ion source with the electric field intensity on the order of MV/m in the radial direction; this plasma sheath will accelerate ions and decelerate electrons. Compared with Ti <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ion, the radial dispersion phenomenon of D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ion is more obvious. The electric field intensity of plasma sheath is first increased and then decreased, which consistently influences the radial dispersion behavior of ions in the expansion cup. Due to the plasma sheath near the wall of the ion source, the ion radial-accelerating effect always exists. Due to the separation between ion and electron, there is also an ion axial-accelerating phenomenon. Moreover, the ion axial-accelerating effect will decrease and, finally, disappear due to the decrease in the separation effect between electron and ion. In the steady phase, the ion current on the extraction wall is higher than the loss of ion current on the wall of the ion source, and the ion extraction efficiency of Ti <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> is much higher than D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> .

Three-Dimensional Analysis of the Influence of the Magnetic Flux Density on Minimum PR in a Faraday-Type MHD Channel

The magnetohydrodynamic (MHD) behavior and performance characteristic have been revealed by 3-D numerical simulation of the Faraday-type MHD generator. Numerical results show that the generator inlet–outlet pressure ratio (PR) will affect the plasma behaviors and generator performance in the channel. At high PR, the plasma flows at supersonic, and higher electric power [enthalpy extraction rate (EE)] can be obtained. However, at low PR, boundary layer separation occurs with deflected flow of velocity streamlines and vortex in the separated flow region, owing to the oblique shock wave. Therefore, there exists a minimum PR to maximize power generation performance. Under the strong MHD interaction, the Lorentz force causes the loss of Mach number and the increase of static pressure, but it can alleviate the effect of oblique shock for a lower PR. Furthermore, suppressing the boundary layer separation effect gradually evolves into a normal shock wave. When PR is higher, the thermoelectric conversion efficiency increases, and then a weak shock wave will be generated in the channel, which will propagate upstream and evolve into a normal shock wave. Consequently, under a higher magnetic flux density, the minimum PR can be effectively reduced, and the best generator performance can be obtained. In addition, an “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula> ”-shaped velocity profile will be generated due to the significantly increased MHD interaction. The results calculated in the present simulation are valuable and important for setting working gas conditions and evaluating generator performance.

Optical time-of-flight and spectroscopic investigation of laser produced barium plasma in presence of magnetic field and ambient gas

Optical-time-of-flight and time-resolved spectroscopy of barium ions and neutral have been performed to study the multiple velocity components and spectral behaviour of laser-produced barium plasma in the presence of ambient gas and magnetic field. Initial structured temporal profiles of ionic and neutral species in vacuum due to different velocity components get more pronounced in the presence of ambient gas, magnetic field and combination of both. Multi-Shifted Maxwell-Boltzmann distribution functions are used to analyse different velocity components. Each component behaves differently with ambient gas and magnetic field which is reflected in their shape and intensity variation. The observed results are explained on the basis of characteristic expansion of the plasma plume under different ambient conditions and possible role of excitation and ionization processes.

Damage evolution behavior of cold plasma treated glass fiber/vinyl ester resin composites under bending load by acoustic emission

This study reveals the preparation and mechanical characterization of cold plasma treated glass fiber/vinyl ester resin composites. The surface characteristics and bending failure mechanism of composites treated by oxygen, argon and nitrogen glow discharge plasma were studied by acoustic emission. The results showed that the bending resistance of argon plasma treated glass fiber reinforced composites exhibited highest. The composite treated by oxygen plasma produced AE signals with a frequency of more than 300 kHz, indicating that the fiber was damaged and the material was brittle, which reduced the strength and plasticity of the material. The bending stress in warp direction was greater than that in weft direction. The bending resistance of the cold plasma treated glass fiber/vinyl ester resin composites was the highest under the conditions of power 150W, flow rate 10sccm and time 120s.

Transverse instability of dust acoustic solitary waves in magnetized dusty plasma composed of vortex-like distribution ions

The dynamical behaviors of dusty plasma can be described by a (3+1)-dimensional modified Zakharov-Kuznetsov equation (mZKE) when the distribution of ions is vortex-like. The critical stable conditions for the line solitons are obtained by the linear stability analysis, which are also confirmed by the nonlinear dynamic evolution. An interesting phenomenon is found from the numerical results, maybe the first time, that the unstable line solitons of the mZKE will evolve into one or more completely localized soliton(s) after a long time evolution. Subsequently, we numerically studied the collision process of two line solitons. The results show that two stable line solitons can restore to their original states. However, if one of the two solitons or both of them are unstable, one or more completely localized solitons will appear during the collision. The results indicate that there are both elastic and inelastic collisions between line solitons.

Effects of Graphene Nanoplatelets on the Microstructure, Mechanical Properties, and Corrosion Behavior of Spark Plasma Sintered Al + 20 vol.% (TiC + TiB2) Hybrid Composites

Effects of Graphene Nanoplatelets on the Microstructure, Mechanical Properties, and Corrosion Behavior of Spark Plasma Sintered Al + 20 vol.% (TiC + TiB2) Hybrid Composites

ASTI: Data assimilation system for particle and heat transport in toroidal plasmas

ASTI, a data assimilation system for integrated transport simulation of fusion plasma, has been developed to predict and control the fusion plasma behavior. ASTI employs the ensemble Kalman filter (EnKF) and smoother (EnKS) as data assimilation methods and the integrated transport simulation code for helical fusion plasma, TASK3D, as the system model. ASTI assimilates the time-series data of measured temperature and density radial profiles into the particle and heat transport simulation. In this study, we consider the uncertainties included in the density, temperature, transport model, neutral beam injection (NBI) heating model, and particle source model. We apply ASTI to 12 experimental data sets of the NBI-heated plasma in Large Helical Device (LHD) and investigate the validity of estimation and the prediction performance of ASTI. The obtained radial profile and time evolution of density, electron temperature, and ion temperature agree well with the experimental data sets. Faster and more accurate integrated transport simulation is realized byASTI than the previous integrated simulation of fusion plasmas.

Study on divertor plasma behavior through sweeping strike point in new lower divertor on EAST

A series of L-mode discharges have been conducted in the new ‘corner slot’ divertor on the Experimental Advanced Superconducting Tokamak (EAST) to study the divertor plasma behavior through sweeping strike point. The plasma control system controls the strike point sweeping from the horizontal target to the vertical target through poloidal field coils, with keeping the main plasma stability. The surface temperature of the divertor target cools down as the strike point moves away, indicating that sweeping strike point mitigates the heat load. To avoid the negative effect of probe tip damage, a method based on sweeping strike point is used to get the normalized profile and study the decay length of particle and heat flux on the divertor target λ js, λ q. In the discharges with high radio-frequency (RF) heating power, electron temperature T e is lower and λ js is larger when the strike point locates on the horizontal target compared to the vertical target, probably due to the corner effect. In the Ohmic discharges, λ js, λ q are much larger compared to the discharges with high RF heating power, which may be attributed to lower edge T e.

Investigation into the formation of Ni splats plasma-sprayed on to mild steel and stainless steel substrates

The present study investigates the splat formation behaviour of Ni particles plasma sprayed onto AISI 1008 mild steel and 316 austenitic stainless steel substrates to draw a comparative analysis of splat formation on both surfaces. A range of analytical techniques were used to analyse the surface and cross-sectional characteristics of the splats formed on both substrates. Most of the splats observed on both of the substrates were halo type splats driven by Rayleigh–Taylor instabilities. A linear relationship was identified between the size of the central core of the splats and their outer ring of debris, which was distinct for each substrate. The diffusion profile, obtained through STEM-EDS analysis, revealed a higher degree of diffusion across the interface between splat and stainless steel substrate as compared to mild steel, suggesting a better bond efficiency for stainless steel. Cross-sectional observations, together with theoretical calculations, showed evidence of substrate melting as well as the presence of metallurgical bonds for both mild steel and stainless steel substrates.

Helium injection plasmas in FTU

In order to extend observations on the increase of electron density peaking in neon doped plasmas, already reported in FTU Mazzotta et al (2015 Nucl. Fusion 55 073027), some sessions have been performed by injecting helium gas on the L-mode plasmas during the last two experimental campaigns. This favorable scenario, which can fall within so called ‘highly radiative’ or ‘plasma detachment’ themes, is investigated in this paper. The description of the impact of the helium injection on plasma behavior, by varying plasma parameters and shape, is exposed, especially with respect to the density peaking and edge conditioning. It has been recorded that, not only the total amount of puffed helium, but also the injection rate intervenes in triggering a particle inflow. Finally, by using VUV spectroscopy measurements, a model to estimate concentrations of impurities is outlined here for the first time, in this way the helium amount is deduced.