Hasil untuk "Plasma engineering. Applied plasma dynamics"

S. Vepřek, M. Venugopalan

T. Desmet, R. Morent, N. De Geyter et al.

Haitang Yang, Bin Yu, Pingan Song et al.

Abstract Flexible polyurethane foams (FPUFs) have been extensively used in furniture, carpet, automobiles, etc., due to their superior thermal insulation, low bulk density and superior chemical resistant properties. Unfortunately, they are extremely ignitable and flammable, and release a large amount of combustion heat accompanied by plenty of smoke and toxic gases upon ignited, thus posing a potential threat to lives and property. The minimization of their fire hazards is usually realized by the addition of flame retardants, and the creation of flame retardant coating. As compared with the former approach, the surface coating strategy has gained much more interests because it improves the flame retardancy of FPUFs without compromising mechanical properties. To date, several surface-coating approaches, including in situ deposition, sol-gel process, plasma technique and layer-by-layer (LBL) assembly have been developed for improving the fire safety performance of FPUFs. This review focuses on the recent advances in flame retarded FPUFs by employing the surface coating approaches. This work also summarizes the design of intumescent and non-intumesecent fire retardant coatings applied to the fire protection of FPUFs by depositing (nano)coatings on their surfaces. Special attention will be paid to the FPUFs treated with flame retardant nanocoating via the LBL assembly. Moreover, this work further compares the advantages and disadvantages of these surface coating methods, and finally presents some future research opportunities on flame retardant FPUFs materials.

U. Asghar, M. Asjad, Yasser Salah Hamed et al.

This paper comprehensively analyzes exact solutions for the nonlinear long-short wave interaction system within the optical field. Consider two general techniques in this field, the Sardar sub-equation method, and a new auxiliary-equation technique. These methods are applied to derive a wide range of soliton solutions for nonlinear partial differential equations. By transforming the original partial differential equation into an ordinary differential equation using an appropriate transformation, various types of solitary wave solutions are obtained. The novelty of this work lies in the application of two powerful analytical methods. The study significantly broadens the scope of these techniques and their applications, providing a diverse set of exact solutions. To enhance comprehension, the obtained solutions are visualized through 3D, 2D, contour, and density plots, offering clear insights into the dynamics of solitary waves. Long-short-wave interaction model has many applications in different kinds of areas such as in optical fiber communication, to understand the interaction between different wave components that can influence the transmission of signals. This model is used to study the interaction between ion-acoustic waves and electron plasma waves. This helps in understanding energy transfer and wave stability in plasma, which is essential for applications like fusion energy research and space plasma. This is important in coastal engineering for predicting wave behaviors that affect coastal structures, sediment transport, and tsunami dynamics.

Wei Liu, Weizong Wang, Yifei Li

The planar Hall thruster (PHT) eliminates the channel wall of the traditional Hall thruster to avoid the plasma erosion-induced decrease in thruster performance and operation lifetime, which has promising application prospects for future complex space missions. However, the nature of electrostatic instabilities and the anomalous electron transport in PHTs remain unknown. In this paper, the PHT discharge is numerically investigated by a 2D-3V collision-less PIC model in the axial-azimuthal plane. The calculated oscillation dominant frequency is compared with the measured data by the ion saturation probe, and satisfactory agreements are reached. Insights into the spatiotemporal dynamics of the plasma characteristics in the PHT are provided. Short-wavelength azimuthal waves, large-scale azimuthal turbulence, and axial modes are observed during the discharge. The wavenumber–frequency power spectra reveal that the azimuthal oscillations correspond to the electron drift instability evolving towards the ion-acoustic mode, and the axial mode is associated with the ion transit-time instability (ITTI). The excitation of ITTI is closely linked to double-layer instability driven by variations in electron transport. Besides, the relationship between the enhanced cross-field current and plasma fluctuations is established. The azimuthal instabilities dominate the formation of the cross-field electron current through the coherence between the electron density and azimuthal electric field, while the axial ITTI significantly influences transport dynamics via nonlinear interactions that generate large-scale azimuthal turbulent structures. Finally, the effect of the imposed ion current densities on the instabilities is explored. The transition to turbulence in the azimuthal mode, along with oscillations in the ion velocity, is observed at low current densities. These results provide a new physical description of the PHT from the perspective of discharge instabilities, which serves as a foundation for future operating condition selection and the development of fully predictive engineering models.

Xinchen Jiang, Yuejiang Shi, Shao-dong Song et al.

ENN He Long-2 (EHL-2) is the next-generation large mega-Ampere (MA) spherical torus (ST) proposed and funded by the ENN company. The design parameters are: T i0 > 30 keV, , I p ~ 3 MA, B t ~ 3 T. One of the biggest challenges of EHL-2 is how to achieve several MA current flat-tops with limited voltage-seconds (Vs) of the center solenoid (CS) coils. In order to minimize the consumption of Vs, a fully non-inductive start-up by electron cyclotron resonance heating (ECRH) will be applied in EHL-2. The ramp-up phase will be accomplished with the synergetic mode between the CS and non-inductive methods. The strategy of non-inductive start-up and ramp-up with synergetic mode has been verified on EXL-50U’s experiments. Based on this strategy, numerical simulations indicate the feasibility of EHL-2 achieving 3 MA plasma current. A high-performance steady-state scenario with I p ~ 1.5 MA is also designed. In this scenario, the bootstrap current fraction f BS > 70%, the safety factor q at the magnetic axis q 0 > 2, the minimum safety factor q min > 1, the poloidal beta β p > 3 and normalized beta β N > 2.3. Each design iteration integrates the validation of physical models with the constraints of engineering implementation, gradually optimizing the performance of the heating and current drive (H&CD) systems. Numerical simulation results for general auxiliary H&CD systems such as neutral beam injection (NBI), electron cyclotron (EC) wave, ion cyclotron wave (ICW), and lower hybrid wave (LHW) are presented. These simulation results ensure that the 31 MW H&CD systems comprehensively cover all scenarios while maintaining engineering feasibility.

G.Y. Yusuf, J. Sabi’u, Ibrahim Sani Ibrahim et al.

In this article, we derive various exact solutions and patterns for the complex modified Korteweg–De Vries system of equation (cmKdV) with a generalized innovative extended direct algebra method. The Korteweg-De Vries system exhibits the scientific dynamics of water particles at the surface and beyond the surface level. The system also has applications in ferromagnetic materials, nonlinear optics, and solitons theory. The innovative direct algebra method is applied to obtain dark, multiple, singular, breather and bright wave patterns. This method also provides staggering wave solutions for the complex modified Kortweg-De Vries system in the form of hyperbolic and trigonometric functions. These recovered solutions for the considered model and are more efficient, concise and general than the extant ones. The wave patterns are properly explained with 2-D and 3-D graphs to elucidate wave behaviour for some selected solutions derived for the system. Lastly, the solutions in this work will greatly advance various fields of application of the Kortweg-De Vries equation like optical fibres, ferromagnetic materials, nonlinear optics, signal processing, water waves, plasma physics, soliton theory, string theory and other contemporary sciences.

K. Bera, Abhishek Verma, S. Ganta et al.

An understanding of the plasma dynamics of radio-frequency (RF) hollow cathode discharges (HCDs) at low to moderate pressures is important due to their wide range of applications. A HCD consists of a hollow cylindrical cavity in the RF-powered cathode separated from a grounded electrode by a dielectric. In RF HCDs, RF sheath heating can play a significant role in plasma production in addition to secondary electrons. In this study, a single hollow cathode hole is modeled using the particle-in-cell/Monte Carlo collision (PIC-MCC) technique at low pressure, where kinetic effects are important. Characterization of a single hollow cathode using PIC-MCC simulation is, however, computationally expensive. For improved computational efficiency, a neural network modeling framework has been developed using the temporal variations of applied RF voltages as input and the electrode current as output. A space-filling design for computational experiments is used, where the variables include the RF voltage at the fundamental frequency, RF voltage at the second harmonic, and their phase difference. The predictions of the electrode current using the trained neural network model compare well with the results of the PIC/MCC simulations, but at a significantly lower computational cost. The neural network model predicts the current very well inside the training domain, and reasonably well even outside the training domain considered in this study.

T. Passot, S. S. Cerri, C. Granier et al.

A Hamiltonian two-field gyrofluid model is used to investigate the dynamics of an electron-ion collisionless plasma subject to a strong ambient magnetic field, within a spectral range extending from the magnetohydrodynamic (MHD) scales to the electron skin depth. This model isolates Alfvén, Kinetic Alfvén and Inertial Kinetic Alfvén waves that play a central role in space plasmas, and extends standard reduced fluid models to broader ranges of the plasma parameters. Recent numerical results are reviewed, including (i) the reconnection-mediated MHD turbulence developing from the collision of counter-propagating Alfvén wave packets, (ii) the specific features of the cascade dynamics in strongly imbalanced turbulence, including a possible link between the existence of a spectral transition range and the presence of co-propagating wave interactions at sub-ion scales, for which new simulations are reported, (iii) the influence of the ion-to-electron temperature ratio in two-dimensional collisionless magnetic reconnection. The role of electron finite Larmor radius corrections is pointed out and the extension of the present model to a four-field gyrofluid model is discussed. Such an extended model accurately describes electron finite Larmor radius effects at small or moderate values of the electron beta parameter, and also retains the coupling to slow magnetosonic waves.

Zetao Lin, Thibault Maurel--Oujia, Benjamin Kadoch et al.

Confinement quality in fusion plasma is significantly influenced by the presence of heavy impurities, which can lead to radiative heat loss and reduced confinement. This study explores the clustering of heavy impurity, \textit{i.e.}, Tungsten in edge plasma, using high-resolution direct numerical simulations of the Hasegawa--Wakatani equations. We use Stokes number to quantify the inertia of impurity particles. It is found that particle inertia will cause spatial intermittency in particle distribution and the formation of large-scale structures, \textit{i.e.}, the clustering of particles. The degrees of clustering are influenced by Stokes number. To quantify these observations, we apply a modified Voronoi tessellation, which assigns specific volumes to impurity particles. By determining time changes of these volumes, we can calculate the impurity velocity divergence, which allows to assess the clustering dynamics. To quantify the clustering statistically, several approaches are applied, such as probability density function (PDF) of impurity velocity divergence and joint PDF of volume and divergence.

Luca Barbieri, Emanuele Papini, Pierfrancesco Di Cintio et al.

Prompted by the relevant problem of temperature inversion (i.e. gradient of density anti-correlated to the gradient of temperature) in astrophysics, we introduce a novel method to model a gravitationally confined multi-component collisionless plasma in contact with a fluctuating thermal boundary. We focus on systems with anti-correlated (inverted) density and temperature profiles, with applications to solar physics. The dynamics of the plasma is analytically described via the coupling of an appropriated coarse-grained distribution function and temporally coarse-grained Vlasov dynamics. We derive a stationary solution of the system and predict the inverted density and temperature profiles of the two-species for scenarios relevant for the corona. We validate our method by comparing the analytical results with kinetic numerical simulations of the plasma dynamics in the context of the two-species Hamiltonian mean-field model (HMF). Finally, we apply our theoretical framework to the problem of the temperature inversion in the solar corona obtaining density and temperature profiles in remarkably good agreement with the observations.

Zenovij Stotsko, O. Kuzin, M. Kuzin

The problem of managing the durability of products due to the creation of regions in materials with a given temporal and spatial non-locality is considered. A mathematical model of softening of materials under the action of external loads is proposed, allowing to take into account the special role in the formation of damaged places of exit of grain boundaries and their triple junctions on the outer surfaces of parts, as well as their interaction with stress concentrators formed after mechanical processing. The developed model representations are used to ensure the operational uniformity of structural elements with concentrators under stress by methods of surface engineering, in particular, when determining the role of changes in the quantitative parameters of the microstructure on the wear resistance of the surface layers of rolling stock parts of railway transport containing stressed concentrators. The optimal depth of the plasma hardening of the subsurface layers of the rims of wheel pairs of locomotives has been established, depending on the size, placement and geometric characteristics of the tension concentrators. It is shown that taking into account the dynamics of structural changes during the degradation of materials in the conditions of operation according to the proposed model ratios allows to achieve the specified life cycle of parts at minimal costs. Increasing the durability of products is achieved by optimizing technological modes of surface engineering, which ensure the formation of structures with a smaller gradient of properties.

G. Dose, S. Roccella, F. Romanelli

A substantial contribution of the stresses that arise inside the Plasma-Facing Components (PFCs) when a heat load is applied is caused by the mismatch of the Coefficient of Thermal Expansion (CTE) between the armor, usually made of tungsten (W), and the heat sink. A potential way to reduce such contribution to the secondary stresses is the use of an interlayer made with a Functionally Graded Material (FGM), to be interposed between the two sub-components. By tailoring the W concentration in the volume of the FGM, one can engineer the CTE in such a way that the thermal stresses are reduced inside the PFC. To minimize and, theoretically, reduce to zero the stresses due to the CTE mismatch, the FGM should ensure kinematic continuity between the armor and the heat sink, in a configuration where they deform into exactly the shape they would assume if they were detached from each other. We will show how this condition occurs when the mean thermal strain of each sub-component is the same. This work provides a methodology to determine the thickness and the spatial concentration function of the FGM able to ensure the necessary kinematic continuity between the two sub-components subjected to a generic temperature field monotonously varying in the thickness, while remaining stress-free itself. A method for the stratification of such ideal FGM is also presented. Additionally, it will be shown that the bending of the PFC, if allowed by the kinematic boundary conditions, does not permit, at least generally, the coupling of the expansion of the armor and of the heat sink. As an example of our methodology, a study case of the thermomechanical design of a steel-based PFC with an engineered W/steel FGM interlayer is presented. In such an exercise, we show that our procedure of engineering a FGM interlayer is able to reduce the linearized secondary stress of more than 24% in the most critical section of the heat sink, satisfying all the design criteria.

T. Mealy, R. Marosi, F. Capolino

We propose a scheme to calculate the reduced plasma frequency of a cylindrical-shaped electron beam flowing inside of a cylindrical tunnel, based on results obtained from particle-in-cell (PIC) simulations. In PIC simulations, we modulate the electron beam using two parallel, non-intercepting, closely spaced grids which are electrically connected together by a single-tone sinusoidal voltage source. The electron energy and the beam current distributions along the length of the tunnel are monitored after the system is operating at steady-state. We build a system matrix describing the beam’s dynamics, estimated by fitting a $2\,\, {}\times {}2$ matrix that best agrees with the first-order differential equations that govern the physics-based system. Results are compared with the theoretical Branch and Mihran model, which is typically used to compute the plasma frequency reduction factor in such systems. Our method shows excellent agreement with the theoretical model, however, it is also general. Our method can be potentially utilized to determine the reduced plasma frequencies of electron beams propagating in longitudinally uniform beam tunnels (i.e., drift regions) of different transverse cross sections, such as the case of a cylindrical or elliptical electron beam propagating inside of a metallic beam tunnel of cylindrical, square, or elliptical cross section. It can be applied also to electron beams composed of multiple streams.

Zheng Bo, Chenxuan Xu, Zhesong Huang et al.

Li 力 FEI 费, B. Zhao 赵, X. Liu 刘 et al.

To increase the thrust-weight ratio in next-generation military aeroengines, a new integrated afterburner was designed in this study. The integrated structure of a combined strut–cavity–injector was applied to the afterburner. To improve ignition characteristics in the afterburner, a new method using a plasma jet igniter was developed and optimized for application in the integrated afterburner. The effects of traditional spark igniters and plasma jet igniters on ignition processes and ignition characteristics of afterburners were studied and compared with the proposed design. The experimental results show that the strut–cavity–injector combination can achieve stable combustion, and plasma ignition can improve ignition characteristics. Compared with conventional spark ignition, plasma ignition reduced the ignition delay time by 67 ms. Additionally, the ignition delay time was reduced by increasing the inlet velocity and reducing the excess air coefficient. This investigation provides an effective and feasible method to apply plasma ignition in aeroengine afterburners and has potential engineering applications.

S. Baruah, V. Prajapati, R. Ganesh

Lane formation dynamics of driven two-dimensional pair-ion plasmas is investigated in under-damped cases where the effect of particle inertia cannot be neglected. Extensive Langevin dynamics simulations using an OpenMP parallel program are carried out to analyse the effect of obstacle and geometric aspect ratio on lane formation dynamics previously reported in Sarma et al. (Phys. Plasmas, vol. 27, 2020, 012106) and Baruah et al. (J. Plasma Phys., vol. 87, 2021, 905870202). Lanes are found to form when like particles move along or opposite to the applied field direction. Lane order parameter, cumulative order parameter and distribution of the order parameter have been implemented to detect phase transition. The effect of geometric aspect ratio on the stability of lanes is systematically determined in both the presence and absence of an obstacle. Here, a specular reflective boundary condition is implemented to mimic an obstacle. We demonstrate that an obstacle promotes the merging of lanes, and the system gradually transitions to a partially mixed phase with higher value of aspect ratio. The occurrence of lane mixing phenomena at the separation boundary of two oppositely flowing lanes at higher value of aspect ratio is observed. In the presence of an oscillatory electric field, the lane merging tendency is reduced to a large extent as compared to the system where a constant electric field is applied. Furthermore, in the presence of both space- and time-varying electric fields, an appearance of a void is observed on either side of the obstacle. The study finds that the presence of an external magnetic field promotes acceleration of the phase transition process towards the lane mixing phase; it also reveals the existence of electric field drift in the system. Our findings may prove to be useful in understanding the nature of lane dynamics in naturally occurring pair-ion plasma systems as well as their relevance to technological applications that exploit or mitigate self-organization.

T. Goto, K. Ichiguchi, H. Tamura et al.

The e ff ect of the pitch modulation of the helical coils on the core plasma performance of the LHD-type helical fusion reactor has been examined. The analysis of the MHD stability and neoclassical transport for the pitch modulation α = 0 . 0 and 0.1 has been conducted based on the finite-beta equilibrium calculated by the HINT code. It was found that the MHD stability is clearly improved without deteriorating the energy transport property by changing the pitch modulation α from 0.1 to 0.0. The reachable operation region expands to the higher density and the expected fusion gain can increase from ∼ 10 to ∼ 20. Because the change of the pitch modulation α from 0.1 to 0.0 requires only a slight change in the shape of the helical coils, the engineering design including the maintenance method that has been examined for the reactor with α = 0 . 1 can be applied without a major modification.

Jeffersson A. Agudelo Rueda, Daniel Verscharen, Robert T. Wicks et al.

We use 3D fully kinetic particle-in-cell simulations to study the occurrence of magnetic reconnection in a simulation of decaying turbulence created by anisotropic counter-propagating low-frequency Alfvén waves consistent with critical-balance theory. We observe the formation of small-scale current-density structures such as current filaments and current sheets as well as the formation of magnetic flux ropes as part of the turbulent cascade. The large magnetic structures present in the simulation domain retain the initial anisotropy while the small-scale structures produced by the turbulent cascade are less anisotropic. To quantify the occurrence of reconnection in our simulation domain, we develop a new set of indicators based on intensity thresholds to identify reconnection events in which both ions and electrons are heated and accelerated in 3D particle-in-cell simulations. According to the application of these indicators, we identify the occurrence of reconnection events in the simulation domain and analyse one of these events in detail. The event is related to the reconnection of two flux ropes, and the associated ion and electron exhausts exhibit a complex three-dimensional structure. We study the profiles of plasma and magnetic-field fluctuations recorded along artificial-spacecraft trajectories passing near and through the reconnection region. Our results suggest the presence of particle heating and acceleration related to small-scale reconnection events within magnetic flux ropes produced by the anisotropic Alfvénic turbulent cascade in the solar wind. These events are related to current structures of order a few ion inertial lengths in size.