Hasil untuk "Plasma engineering. Applied plasma dynamics"

Hicham Saber, M. Roshid, M. Bouye et al.

This study explores in detail the bifurcation and optical solitons of the third-order nonlinear chiral (2 + 1)-dimensional nonlinear Schrödinger equation (M-fCNLSE) with the M-fractional derivative in nonlinear media. We also discuss the properties of fractional derivatives in this context. Initially, bifurcation theory is utilized to analyze critical points and phase portraits, identifying transitions that give rise to new dynamical behaviors, such as stability shifts or the onset of chaotic motion. The first figure depicts the dynamics of soliton solutions undergoing a saddle-node bifurcation. There are two techniques, namely the polynomial expansion (PE) and the unified solver (US) techniques, that are applied to explore wave propagation in telecommunication systems, nonlinear optics, plasma physics, and quantum mechanics. These methods enable the creation of new optical soliton solutions using hyperbolic, rational, and trigonometric functions. Numerical results, presented in 2D and 3D diagrams, demonstrate the behavior of the solutions. The polynomial expansion technique generates diverse periodic optical soliton solutions, including double-periodic and lump wave solitons. The unified solver technique produces periodic breather waves, double-periodic waves, and other complex wave structures. Additionally, two-dimensional graphs display the effects of the truncated M-fractional parameters for \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$P=0.1, 0.5, 0.75, 0.9$$\end{document}. Overall, this investigation and the proposed techniques provide valuable tools for generating precise optical soliton solutions, which have significant applications in optical communications, nonlinear optics, and engineering.

Yuejiang Shi

One mega ampere (MA) plasma discharges were achieved on the EXL-50U spherical torus (ST) in hydrogen-boron (p-B) plasmas with toroidal fields up to 1 T at major radii up to 0.6m. A key innovation in these experiments was the use of a boron-rich fueling strategy, incorporating a high-concentration boron-containing gas mixture and real-time boron powder injection during the discharges. The boron content in the fueling reached 10%, representing the first publicly reported MA-class hydrogen-boron plasma with such a high boron concentration. Non-inductive plasma startup was achieved using electron cyclotron resonance heating (ECRH), and a rapid current ramp-up to 1 MA was realized through the synergistic use of ECRH and the central solenoid (CS). With 800 kW of ECRH power, core electron temperatures of up to 3 keV were attained. These results demonstrate the feasibility of producing high-performance hydrogen-boron plasmas in a spherical torus configuration and offer important physics and engineering insights for future reactor-scale applications - particularly in the areas of low loop voltage current start-up and real-time boronization techniques.

Y.Y. Kim, J.Y. Park, S.U. Lee et al.

Nanosecond pulse dielectric barrier discharge (NPDBD) is a highly energy-efficient method for decomposing volatile organic compounds (VOCs). However, accurately measuring the energy delivered to the plasma in nanosecond pulse systems is challenging due to parasitic components inherent in the system's electrical characteristics. This study validates methods for precise energy measurement in NPDBD systems and evaluates the energy efficiency of toluene decomposition. A circuit simulation model was developed to account for transmission line effects, incorporating parameters such as parasitic resistance, capacitance, inductance, and plasma dynamics. The simulation results were compared with experimental data, demonstrating a precise method for measuring discharge current and energy. Toluene decomposition experiments performed under varying applied voltage and pulse width conditions demonstrated an energy efficiency range of $30-45 \mathrm{g} / \text{kWh}$. The validated measurement methods provide a foundation for evaluating VOC removal in NPDBD systems and contribute to the design of more efficient electrical conditions for industrial applications.

L. Scarivaglione, S. Servidio

Understanding turbulence via simplified fluid models is crucial for optimizing magnetic confinement in tokamak devices. In this work, we propose a novel high-order turbulence law that describes the turbulent cascade at the edges of fusion plasmas, namely valid within the scrape-off layer (SOL), in the framework of the Braginskii fluid model. Using the Yaglom–Monin approach, we derive an exact relation characterizing density fluctuations in these strongly magnetized systems. We obtain a third-order von Kármán–Howarth equation in increment form for the case of electrostatic Braginskii model, applied to a decaying turbulence regime. The new Yaglom–Braginskii law is validated through direct numerical simulations within a reduced (two-dimensional) model. Our analysis reveals that the plasma dynamics obey the cross-scale balance, exhibiting a well-defined inertial range of turbulence. This third-order law can provide an accurate measure of the cascade rate of density fluctuations in the SOL of laboratory plasmas.

Mozhdeh Hooshyar, C. Dumitrache

This study investigates the applicability of a CW laser for a femtosecond filament lifetime extension. Initially the formation of the filament is modeled using a zero-dimensional semi-analytical collisionless model that accounts for the generation of photoelectrons in the high-intensity field of the fs-pulse. The filament post-discharge phase and the subsequent CW addition are modeled using a comprehensive (radial) 1-D axisymmetric model, incorporating both plasma dynamics and chemical kinetics. The model self-consistently integrates the Navier–Stokes fluid flow equations with the conservation of electron energy and vibrational energy within the plasma to account for non-equilibrium flow effects. The results show that the femtosecond filament (Ifs= 5 × 1013 W/cm−2) leads to strong dissociation of air molecules during the post-discharge but very little gas heating (Tgas ∼ 450 K). The filament decays quite rapidly at 30 bar, with the electron density decaying by more than four orders of magnitude during the first 100 nanoseconds after the pulse. Both results are in good agreement with past experimental observations. Interestingly, overlapping a CW laser beam ( ICW=1×1013 W/cm−2) on the fs-pulse at 30 bar is shown to slow down the electron number density decay and stabilize the electron temperature to ∼ 0.7 eV. The ability to extend the femtosecond filament lifetime using a CW laser could be applied to develop an electrodeless continuous optical discharge for various practical applications in spectroscopy, material processing, plasma medicine or plasma-assisted combustion.

P. Helander, R. J. J. Mackenbach

The available energy of a plasma is defined as the maximum amount by which the plasma energy can be lowered by volume-preserving rearrangements in phase space, a so-called Gardner re-stacking. A general expression is derived for the available energy of a nearly homogeneous plasma and is shown to be closely related to the Helmholtz free energy, which it can never exceed. A number of explicit examples are given.

Shaun Andrews, Raoul Andriulli, Nabil Souhair et al.

Magnetic nozzles (MN) are known to be subject to anomalous non-collisional diffusion mechanisms driven by instabilities and wave-particle interactions. This study therefore employs a fully kinetic axial-radial particle-in-cell (PIC) model to examine the impact of this anomalous diffusion on plasma transport and the propulsive performance of MNs typical of low-power cathode-less radio-frequency (RF) plasma thrusters. A Bohm-type anomalous collisionality scaling ($ν_{an}=α_{an}ω_{ce}$) is implemented to simulations of the 150 W-class REGULUS-150-Xe thruster, evaluating both low-power (30 W) and high-power (150 W) operating conditions. The impact on azimuthal electron current formation is assessed, as well as its subsequent effect on thrust generation, momentum and power balance, and overall propulsive efficiency. A critical value of the Bohm coefficient was found to exist, where the MN expansion transitions from a well-collimated to an under-collimated state and electron transport shifts from being dominated by magnetic advection to being dominated by cross-field diffusion. This critical transition was found to occur within a narrow interval between $α_{an}$=1/128 and 1/64. Beyond this threshold, it is found that the enhanced cross-field transport of electrons inhibits the formation of the typical MN potential barrier, reducing the radial confinement. The downstream potential drop is reduced by up to 15\%. Diamagnetic electron current is diminished in the absence of steep pressure gradients and the $E\times B$ current becomes purely paramagnetic. The MN efficiency is cut from circa 0.5 to 0.2 due to loss of electron thermal energy conversion and increased plume divergence. At the Bohm limit of $α_{an}=1/16$, agreement to experimental thrust profiles of $<20\%$ is achieved in contrast to 48\% overestimation at high-power in the classical case.

Daniel Seipt, Alec G. R. Thomas

The investigation of spin and polarization effects in ultra-high intensity laser-plasma and laser-beam interactions has become an emergent topic in high-field science recently. In this paper we derive a relativistic kinetic description of spin-polarized plasmas, where QED effects are taken into account via Boltzmann-type collision operators under the local constant field approximation. The emergence of anomalous precession is derived from one-loop self-energy contributions in a strong background field. We are interested, in particular, in the interplay between radiation reaction effects and the spin polarization of the radiating particles. For this we derive equations for spin-polarized quantum radiation reaction from moments of the spin-polarized kinetic equations. By comparing with the classical theory, we identify and discuss the spin-dependent radiation reaction terms, and radiative contributions to spin dynamics.

Kyungtak Lim, Maurizio Giacomin, Paolo Ricci et al.

The effect of triangularity on tokamak boundary plasma turbulence is investigated by using global, flux-driven, three-dimensional, two-fluid simulations. The simulations show that negative triangularity stabilizes boundary plasma turbulence, and linear investigations reveal that this is due to a reduction of the magnetic curvature drive of interchange instabilities, such as the resistive ballooning mode. As a consequence, the pressure decay length $L_p$, related to the SOL power fall-off length $λ_q$, is found to be affected by triangularity. Leveraging considerations on the effect of triangularity on the linear growth rate and nonlinear evolution of the resistive ballooning mode, the analytical theory-based scaling law for $L_p$ in L-mode plasmas, derived by Giacomin \textit{et al.} [{Nucl. Fusion}, \href{https://doi.org/10.1088/1741-4326/abf8f6}{\textbf{61} 076002} (2021)], is extended to include the effect of triangularity. The scaling is in agreement with nonlinear simulations and a multi-machine experimental database, which include recent TCV discharges dedicated to the study of the effect of triangularity in L-mode diverted discharges. Overall, the present results highlight that negative triangularity narrows the $L_p$ and considering the effect of triangularity is important for a reliable extrapolation of $λ_q$ from present experiments to larger devices.

T. Wang 王, Shizhao 士朝 WEI 魏, S. Briguglio et al.

In a tokamak fusion reactor operated at steady state, the equilibrium magnetic field is likely to have reversed shear in the core region, as the noninductive bootstrap current profile generally peaks off-axis. The reversed shear Alfvén eigenmode (RSAE) as a unique branch of the shear Alfvén wave in this equilibrium, can exist with a broad spectrum in wavenumber and frequency, and be resonantly driven unstable by energetic particles (EP). After briefly discussing the RSAE linear properties in burning plasma condition, we review several key topics of the nonlinear dynamics for the RSAE through both wave-EP resonance and wave-wave coupling channels, and illustrate their potentially important role in reactor-scale fusion plasmas. By means of simplified hybrid MHD-kinetic simulations, the RSAEs are shown to have typically broad phase space resonance structure with both circulating and trapped EP, as results of weak/vanishing magnetic shear and relatively low frequency. Through the route of wave-EP nonlinearity, the dominant saturation mechanism is mainly due to the transported resonant EP radially decoupling with the localized RSAE mode structure, and the resultant EP transport generally has a convective feature. The saturated RSAEs also undergo various nonlinear couplings with other collective oscillations. Two typical routes as parametric decay and modulational instability are studied using nonlinear gyrokinetic theory, and applied to the scenario of spontaneous excitation by a finite amplitude pump RSAE. Multiple RSAEs could naturally couple and induce the spectral energy cascade into a low frequency Alfvénic mode, which may effectively transfer the EP energy to fuel ions via collisionless Landau damping. Moreover, zero frequency zonal field structure could be spontaneously excited by modulation of the pump RSAE envelope, and may also lead to saturation of the pump RSAE by both scattering into stable domain and local distortion of the continuum structure.

F. Liang, L. Miao, F. Tian et al.

The electrodynamic tether technology is a new method for space propulsion. When an electrodynamic tether runs on a low-Earth-orbit, a bare conductive tether with current flow will interact with the geomagnetic field to generate Lorentz force exerted on the tether. To generate current in the long conductive tether, the electrodynamic tether should exchange electrons with the surrounding space plasma. In the process of electrons exchange, electrons are collected from space plasma by the bare conductive tether. Almost all the existing studies took the orbital motion limited theory to describe the process of electrons collection and calculate the value of current in the tether, but the orbital-motion-limited theory is insufficient when some non-ideal situations are considered, such as the flow rate of the surrounding plasma, the cyclotron motion of electron effected by geomagnetic field, and the irregular shape of tether, etc. In this work, a complicated analytical model of electrons collection is firstly established based on the Spacecraft Plasma Interaction Software (SPIS). The values of current in the conductive tether effected by non-ideal factors are calculated. The analytical model is used to correct the value of orbital-motion-limited current. A de-orbiting dynamics model of electrodynamic tether including the analytical model of electrons collection is then established. The variation of de-orbiting dynamics of electrodynamic tether under the effects of non-ideal factors is studied.

Quanzhi Zhang, Jia‐Rui Liu, Yong-Xin Liu et al.

An enhanced electron heating mechanism based on a resonance between the cyclotron motion of electrons and radio frequency (rf) electric field in the plasma bulk is reported in weakly magnetized capacitively coupled argon plasmas at low pressure. When the electron cyclotron frequency coincides with the applied power source frequency, the bulk electrons can continuously acquire energy from the background electric field within certain rf periods during the cyclotron motion, inducing overall distinct increase of excitation rate and electron temperature in the plasma bulk. This enhanced electron heating effect has been examined by a combination of kinetic particle simulations, experimental measurements, and an analytical model, and the dynamics of electrons are revealed at resonant conditions.

Ibrahim-Elkhalil Ahmed, A. Abouelregal, D. M. Mostafa

R. Mahamud

A two-dimensional (2D) and three-temperature mathematical model for dual-pulse laser (DPL) ignition was applied to study the mechanism of the nonequilibrium plasma (NEQP) process during DPL energy deposition. The 2D model could predict the influence of the reaction kinetics and nonequilibrium effects on the ignition delay time and kernel dynamics. As the plasma reaction rates were extremely fast compared with the combustion reaction rates, it can be predicted that the variability of the plasma lifetime will directly influence the ignition delay time and reaction kinetics. The results suggested that the energy relaxation rate from the electronic state was rapid compared to that from the vibrational state due to the short lifetime of the plasma state. However, the relatively slower energy relaxation from the vibrational state provided long-term thermalization of the ignition kernel. For the same level of energy deposition, the NEQP system predicted a higher rate of vorticity generation, signifying a higher level of mixing and baroclinicity production. The results also suggested that ignition in a premixed fuel airflow required a higher degree of energy deposition, due to a higher rate of radical and thermal losses.

M. A. Shakoori, M. He, A. Shahzad et al.

The effects of external electric field (E) on the diffusion coefficient of dust particles in low-temperature dusty plasmas (LT-DPs) have been computed through nonequilibrium molecular dynamics (NEMD) simulations. The new simulation result was obtained by employing the integral formula of velocity autocorrelation functions (VACF) using the Green-Kubo relation. The normalized self-diffusion coefficient (D*) is investigated for different combinations of plasma coupling (Γ) and Debye screening (κ) parameters. The simulation outcome shows that the decreasing position of D* shifts toward Γ and also increased with the increase of κ. The D* linearly decreased with Γ and increased when applied external E increases. It is observed that the increasing trend of D* depends on the E strength. These investigations show that the present algorithm provides precise data with fast convergence and effects of κ, Γ, E. It is shown that the current NEMD techniques with applied external E can be employed to understand the microscopic mechanism of dusty plasmas.

Mingyue Han, Yang Luo, Liuhe Li et al.

Investigating the ion dynamics in the emerging bipolar pulse high power impulse magnetron sputtering (BP-HiPIMS) discharge is necessary and important for broadening its industrial applications. Recently, an optimized plasma source operating the BP-HiPIMS with an auxiliary anode and a solenoidal coil is proposed to enhance the plasma flux and energy, named as ACBP-HiPIMS (‘A’-anode, ‘C’-coil). In the present work, the temporal evolutions of the ion velocity distribution functions (IVDF) in BP-HiPIMS and ACBP-HiPIMS discharges are measured using a retarding field energy analyser (RFEA). For the BP-HiPIMS discharge, operated at various positive pulse voltages U +, the temporal evolutions of IVDFs illustrate that there are two high-energy peaks, E 1 and E 2, which are both lower than the applied U +. The ratio of the mean ion energy E i,mean to the applied U + is around 0.55–0.6 at various U +. In ACBP-HiPIMS discharge, the IVDF evolution shows three distinguishable stages which has the similar evolution trend with the floating potential V f on the RFEA frontplate: (i) the stable stage with two high-energy peaks (E 2 and E 3 with energy respectively lower and higher than the applied U + amplitude) when the floating potential V f is close to the applied positive pulse voltage; (ii) the transition stage with low-energy populations when the V f drops by ∼20 V within ∼10 μs; and (iii) the oscillation stage with alternating E 2 and E 3 populations and ever-present E 1 population when the V f slightly decreases until to the end of positive pulse. The comparison of IVDFs in BP-HiPIMS and ACBP-HiPIMS suggests that both the mean ion energy and high-energy ion flux have been effectively improved in ACBP-HiPIMS discharge. The formation of floating potential drop is explored using the Langmuir probe which may be attributed to the establishment of anode double layer structure. The acceleration of ion at the double layer boundary is analysed using a theoretical model, in this way to clarify the oscillation in IVDF evolutions in ACBP-HiPIMS discharge.

I. Matveev

This article provides the description of a qualitative physical model of the boron nitride nanotubes (BNNTs) formation in plasma. This model combines understanding not only chemistry of the process, which is well known, but also gas dynamics, heat and mass transfer, and interactions in a complicated multiphase swirling and highly reactive flow of solids, gases, and plasma. The model offers a concept for predicting and controlling phenomena of the BNNTs formation. It is universal and could be applied not only for boron and N2 plasma but also for a wide variety of solids and plasma gases. It will help to navigate research and focus their efforts on collecting and analyzing numerical data for statistical analysis, further development of a quantitative model, and design and production of new nanomaterials with targeted properties. Inductively coupled or radio frequency plasma sources are selected as the best candidates for providing chemically pure plasma due to their electrodeless design and virtually unlimited service time on different gases and blends and from vacuum to bar pressure.

A B Blagoev, S K H Auluck

The existence of axial (poloidal) magnetic field in a plasma focus and its significance in plasma focus phenomenology has been extensively discussed in a recent review paper. The poloidal magnetic field is a part of the transient 3-dimensional magnetic field structures which arise spontaneously, accelerate ions and keep them moving in trajectories that repeatedly cross a dense and warm plasma target. This is the origin of the abnormally high fusion reaction rate of the plasma focus, which has been known since the 1960s but has begun to be understood quite recently. Further progress now depends on explorations of the global aspects of the evolution of poloidal magnetic field. However, well-known experimental difficulties involved in standard techniques of axial magnetic field measurement hamper such research efforts. Taking cognizance of this stalemate, the International Scientific Committee for Dense Magnetized Plasmas launched an initiative to address this state of affairs in an International Video Conference on 24th April 2020. This paper reports on the first experiments that resulted from that initiative

F J Gonzalez, J I Gonzalez, S Soler et al.

We describe a procedure to obtain the plasma parameters from the I-V Langmuir curve by using the Druyvesteyn equation. We propose to include two new parameters, $q$ and $r$, to the usual plasma parameters: plasma potential ($V_p$), floating potential ($V_f$), electron density ($n$), and electron temperature ($T$). These new parameters can be particularly useful to represent non-Maxwellian distributions. The procedure is based on the fit of the I-V Langmuir curve with the $q$-Weibull distribution function, and is motivated by recent works which use the $q$-exponential distribution function derived from Tsallis statistics. We obtain the usual plasma parameters employing three techniques: the numerical differentiation using Savitzky Golay (SG) filters, the $q$-exponential distribution function, and the $q$-Weibull distribution function. We explain the limitations of the $q$-exponential function, where the experimental data $V>V_p$ needs to be trimmed beforehand, and this results in a lower accuracy compared to the numerical differentiation with SG. To overcome this difficulty, the $q$-Weibull function is introduced as a natural generalization to the $q$-exponential distribution, and it has greater flexibility in order to represent the concavity change around $V_p$. We apply this procedure to analyze the measurements corresponding to a nitrogen $N_2$ cold plasma obtained by using a single Langmuir probe located at different heights from the cathode. We show that the $q$ parameter has a very stable numerical value with the height. This work may contribute to clarify some advantages and limitations of the use of non-extensive statistics in plasma diagnostics, but the physical interpretation of the non-extensive parameters in plasma physics remains not fully clarified, and requires further research.

D. Beloplotov, V. Tarasenko, V. Shklyaev et al.

The paper is devoted to the study of the initiation and formation of a negative streamer in a sharply inhomogeneous electric field and the generation of runaway electrons (REs) in air and helium at atmospheric pressure and below, as well as in sulfur hexafluoride at low pressure. Nanosecond voltage pulses of negative polarity with an amplitude of 18 kV were applied across a point-to-plane gap 8.5 mm long. The studies were carried out using broadband measuring sensors and equipment with picosecond time resolution, as well as using a four-channel ICCD camera. Using a special method for measuring the dynamic displacement current caused by the redistribution of the electric field during streamer formation, the waveforms of voltage, discharge current, RE current, and dynamic displacement current were synchronized to each other, as well as to ICCD images. Data on the generation of REs with respect to the dynamics of streamer formation were obtained. It was found that REs are generated not only during the breakdown of the gap, but also after that. It has been found that the formation time of explosive emission centers affects the generation of REs after breakdown. Based on the measurement data of the voltage, discharge current, and dynamic displacement current, the electron concentration in the plasma channel after breakdown and the electric field strength near the surface of the grounded electrode were calculated.