ABSTRACT This study presents a machine‐learning‐based method to predict the spatiotemporal evolution of dust particle configurations in two‐dimensional dusty plasmas. Evolutionary datasets are generated via molecular dynamics simulations under the Yukawa potential approximation, and particle configurations are encoded as fixed‐resolution grayscale image sequences. A spatiotemporal recurrent neural network, PredRNN, is adopted to model the structural evolution of dust particles and conduct rolling predictions from a limited number of initial frames. Results demonstrate that PredRNN effectively captures the dynamical behavior of dust particles and yields predictions consistent with molecular dynamics simulations for key structural features, including cluster formation, coalescence, and long‐term evolution. Quantitative evaluations using MSE, SSIM, and LPIPS further validate the model's predictive performance at both structural and perceptual levels. The proposed framework accurately reproduces the self‐organized structural evolution of dust systems and offers a data‐driven perspective for understanding collective self‐organization dynamics in dusty plasmas. It also provides an efficient computational approach for long‐timescale extrapolation.
ABSTRACT Turbulence in the edge and scrape‐off layer regions plays a critical role for the performance of future magnetic confinement fusion power plants. Gyrokinetic simulations allow studying this regime with high fidelity. A key aspect in these regions is the high concentration of impurities, which can radiate energy, leading to significant losses. Due to large mass and high charge state, impurities are highly collisional, making them difficult to model accurately. This work presents discretization and algorithmic improvements for Lenard‐Bernstein collisions in gyrokinetic simulations based on previous conservative finite‐volume scheme. The new discretization improves numerical consistency by eliminating conservation errors, which were previously circumvented through the use of free parameters. While small boundary corrections remain necessary, we show that numerical conservation can be improved through careful stencil design, reducing reliance on free parameters. Its implementation is verified through conservation and relaxation tests. The algorithmic improvements focus on computational performance, achieving compute and communication performance gains in a scaled‐down TCV‐X21 benchmark. It also scales as with the number of species , significantly improving upon the previous naive implementation.
ABSTRACT We examine the reflection of small‐but‐finite amplitude ion‐acoustic‐type solitons from equilibrium density gradients in an inhomogeneous electron–positron–ion (e–p–i) plasma containing negatively charged dust grains. Such gradients can act as effective reflecting interfaces and are relevant in laboratory dusty plasmas, sheath regions, and emerging pair‐plasma experiments. Using the reductive perturbation technique for slowly varying equilibria with finite electron and positron temperatures and initial drifts, we derive coupled modified Korteweg–de Vries (mKdV) equations for the evolution of incident and reflected solitary waves. The resulting phase‐velocity relation shows how key plasma parameters influence soliton propagation. An increase in the positron‐to‐electron temperature ratio raises the phase velocity and produces narrower, higher‐amplitude solitons, whereas increasing dust charge or dust concentration lowers the phase velocity and leads to broader, weaker structures due to enhanced space‐charge screening. Electron drift has a comparatively modest effect and mainly influences the soliton width. The plasma inhomogeneity leads to partial reflection of the incident soliton, and the reflection coefficient is evaluated. Dust charging suppresses reflection, while higher positron temperature enhances it. These results provide a clear physical picture of soliton reflection in dusty e–p–i plasmas and serve as useful benchmarks for laboratory and numerical studies.
ABSTRACT Influence of nitrogen recycling on toroidally asymmetric heat load distribution with nitrogen seeding on the Chinese Fusion Engineering Testing Reactor (CFETR) X‐divertor configuration has been performed by the three‐dimensional (3D) edge fluid transport code package EMC3‐EIRENE. The sensitivity studies of the recycling coefficient of nitrogen ions scanned from 0% to 100% show that the larger recycling coefficients of nitrogen ions lead to a significant increment of nitrogen particle content with different charge‐states in the simulation volume. The increased contributions to total power loss induced by nitrogen impurities are found both for the in‐ and out‐board seeding positions. While the peak values of electron temperature and heat load rapidly decrease with the larger recycling coefficients of nitrogen ions, especially for the high recycling coefficient cases. A more pronounced toroidal asymmetry of heat load distribution is found for the high nitrogen recycling coefficient compared to the low recycling coefficient scenarios. This is attributed to the relatively enlarged deposition area of toroidal nitrogen ions on divertor targets and the higher power loss by nitrogen impurities as the recycling coefficient of nitrogen ions increases.
ABSTRACT The Coaxial Magnetized Plasma Accelerator (CMPA) converts electromagnetic energy into kinetic and thermal plasma flux via self‐induced Lorentz forces. In this study, we develop a magnetohydrodynamic (MHD) numerical model to systematically elucidate the regulatory mechanisms of electrode geometric parameters on plasma jet dynamics. Specifically, we decouple the contributions of three critical geometric parameters, namely, the length and width of the plasma generation channel and the inner diameter of the acceleration channel, and analyze their effects on jet velocity, temperature, and pressure. The results indicate that, under the premise of ensuring discharge stability, a design strategy characterized by an elongated channel, narrow width, and moderate inner diameter should be adopted to achieve efficient conversion of electromagnetic energy into both kinetic momentum and internal energy of the jet. This work provides theoretical support for the structural optimization and performance enhancement of CMPA devices.
ABSTRACT We study melting in two‐dimensional classical particles with Gaussian‐core interactions in both pure and disordered environments. The pure system exhibits conventional two‐step melting described by Berezinskii‐Kosterlitz–Thouless–Halperin–Nelson–Young (BKTHNY) theory, with a hexatic phase separating solid and liquid. Disorder alters this scenario remarkably: random pinning stabilizes a hexatic‐like phase down to zero temperature, which melts directly into a liquid at , whereas commensurate pinning anchors a solid which undergoes a single‐step transition to the liquid at , removing any intervening hexaticity. Thus, in both cases, the two‐step melting of pure systems turns into a one‐step transition. Beyond elucidating the equilibrium phase behavior, with and without disorder, we uncover dynamical signatures of cooperative string‐like motion of particles at very low temperatures. Remarkably, such correlated dynamics, usually associated with structural glasses and supercooled liquids, emerge here within equilibrium phases, in both pure and disordered systems. We further show that impurities, in the form of pinning, enhance such cooperative motions, leading to slow relaxation and departures from diffusive dynamics. Our results highlight the roles of topological defects, impurities, and cooperative dynamics in governing two‐dimensional melting.
In this work, we investigate the formation and propagation of extended dark envelope solitary waves in an unmagnetized, collisionless dusty plasma composed of negatively charged dust grains, electrons, and two-temperature ions. Starting from the fluid and Poisson equations, the nonlinear Schr & ouml;dinger equation (NLSE) governing dust-acoustic waves is derived via the multiple-scale perturbation method, and a generalized non-exact dark soliton solution with adjustable parameters is introduced to examine amplitude and localization effects. Particle-in-Cell (PIC) simulations are conducted to verify the analytical results, showing excellent agreement and confirming the stability and persistence of the dark soliton under parameter variations, thereby providing a solid theoretical and numerical foundation for nonlinear wave dynamics in dusty plasmas.
In this paper, we experimentally investigated the parametric instability of magnetized plasma caused by the action of an external high-frequency electric pumping field in the frequency range ( are the ion and electron langmuir frequencies of the plasma, is the frequency of the external high-frequency electric field), which corresponds to the excitation of lower-hybrid electron and ion oscillations propagating almost across the magnetic field. It has been established that the longitudinal (along the magnetic field) limitation of the plasma volume under certain conditions is a decisive factor determining the threshold characteristics of the parametric process in the lower hybrid frequency range. The given estimates indicate the need to take this factor into account in the practical use of plasma systems based on high-frequency discharges.
This work presents the OpenMP parallelization of the preconditioning Jacobian assembly and right-hand side residual evaluation in UEDGE. A continuation algorithm, utilizing the internal NKSOL implicit Jacobian-Free Newton-Krylov solver to efficiently scan physical parameters, is also presented. The implemented parallelization reduces the computational time for a benchmark scan run on 32 threads by compared to the serial version when using trained random forest regression models to identify the optimal decomposition of the system of equations. Random forest regression models applied to the UEDGE time-dependent and continuation solver algorithms did not yield meaningful improvement in computational performance. A benchmark DIII-D gas injection rate scan in the 0.35-0.75 kA interval, performed on a test cluster using the parallelized code and continuation solver, produced 1066 steady-state solutions with a 22 s average wall-clock computational time per steady-state solution.
Atmospheric pressure non-thermal plasma provides a solvent-free route to tailor the surface chemistry of porous carbons while preserving their bulk structure. Here, we report a cost effective, air-operated KINPen-type plasma jet for the surface functionalization of coconut-shell activated carbon (AC) and correlate plasma conditions with resulting materials changes using optical and material diagnostics. Optical emission spectroscopy (OES) was utilized to deduce the key plasma parameters such as electron temperature (similar to 0.42 eV), rotational temperature (similar to 1210 K), and electron number density (similar to 1016 cm-3). X-ray diffraction (XRD) suggests that the carbon structure is largely maintained after treatment, with no apparent evidence of bulk phase transformation. Raman spectroscopy indicates minor structural modification, consistent with plasma-induced surface activation, while scanning electron microscopy (SEM) signifies enhanced surface roughness and apparent pore development. Energy-dispersive X-ray spectroscopy (EDX) indicates an increase in surface oxygen content, while Fourier-transform infrared spectroscopy (FTIR) shows changes in absorption features within the measured spectral range that are consistent with plasma-induced surface oxidation and modification. Plasma-treated AC shows improved methylene blue removal compared with untreated AC, suggesting that the plasma-induced surface modification can enhance adsorption performance for environmental remediation. The presented approach offers a scalable pathway for engineering porous carbon surfaces using ambient-air plasma at atmospheric pressure.
For JA DEMO, one of the grand challenges is efficiently handling the extreme power loads onto plasma-facing components, particularly the divertor targets. Impurity seeding is an essential strategy for increasing the radiation losses and thereby reducing the heat load on the targets. A critical remaining issue is the trade-off between the retention of radiative impurities in the divertor region to maximize the radiation loss, and their leakage to the upstream region, which degrades the core plasma confinement. To address this issue, based on the current baseline divertor geometry of JA DEMO, the SOLPS-ITER code is applied for the first time to evaluate the divertor power exhaust and Ar impurity distribution across various Ar seeding levels in detail. The simulation results show that increasing the Ar seeding level is highly beneficial for reducing the heat load on the targets. Moreover, in the near SOL there is a strong flow reversal of the main D ions and Ar impurity ions from the lower outer divertor target toward the upstream. This flow reversal promotes the transport of Ar ions out of the lower outer divertor region, leading to significant core contamination. As a result, such leakage severely constrains the viability of using high seeding levels for heat-load control in the current JA DEMO divertor geometry and plasma operating scenario.
The present study explores the three-dimensional wave group dynamics and breather excitations associated with dust-acoustic waves (DAWs) in a superthermal magnetized dusty plasma system. The plasma is assumed to consist of inertialess electrons and ions obeying a kappa distribution, and a negatively charged inertial dust fluid under the influence of an external uniform magnetic field. By employing the reductive perturbation method, we derive the Laedke-Spatschek (LS) equation, which governs the dynamics of the nonlinear DAWs in such a plasma configuration. Analytical solutions of the evolution equation predict a wide class of nonlinear localized structures. Furthermore, the analysis reveals that the modulated wave group dynamics can be effectively described by a -dimensional nonlinear Schr & ouml;dinger equation (NLSE), accounting for both nonlinear and dispersive effects. The regions of stability and instability of the DAW propagation are delineated in the relevant plasma parameter space, identifying the conditions under which rational breather solutions of NLSE, such as the Peregrine soliton, Akhmediev breather, and Kuznetsov-Ma breather can be excited through modulational instability. The findings provide a comprehensive understanding of the proliferation of nonlinear wave modulation and energy localization phenomena in dusty plasma environments, with potential implications for both space and laboratory plasma systems.
The advancement of 3D integration technology has driven demand for micro-scale, high aspect ratio (HAR) through-silicon via (TSV) etching, establishing it as a critical semiconductor manufacturing technology. Current 3D stacking implementations typically utilize TSVs with aspect ratios of approximately 10:1. To enable higher-density interconnects in next-generation applications, achieving substantially higher AR TSVs is imperative. However, within the photoresist (PR) mask system, high aspect ratio TSV etching faces challenges of insufficient etch selectivity and PR mask collapse, both of which constrain further aspect ratio scaling. This study proposes an optimization strategy for key process parameters. Through parametric optimization of chamber pressure, source power, and bias power, we achieved significant enhancement in selectivity and completely eliminated PR mask collapse. Ultimately, an aspect ratio of 25:1 was successfully demonstrated on TSVs with a critical dimension (CD) of 3 mu m.
Resonant magnetic perturbations (RMPs) alter magnetic field topology via island formation and can modify core transport in toroidal fusion devices. Using the global gyrokinetic particle-in-cell code XGC-S, originally developed for stellarator geometries, we quantify how island topology affects neoclassical heat transport in a circular tokamak with RMP-induced islands. Electron radial heat diffusivity exhibits a two-peak structure with a dominant enhancement near the O/X-point region and a secondary peak at the outer island boundary, whereas ion transport remains close to the neoclassical prediction. The observed electron diffusivity is strongly enhanced over the neoclassical baseline but remains well below the Rechester-Rosenbluth estimate, consistent with the non-ergodic character of the island topology. The density dependence of diffusivity is weaker inside the islands than outside, indicating the presence of topology-driven transport channels that do not depend strongly on collisionality. Two-dimensional heat flux maps reveal an up-down antisymmetric structure at the island separatrices consistent with magnetic gradient and curvature drift effects, in contrast to the symmetric temperature flattening inside the islands. These results identify topology-dependent avenues for electron heat transport in RMP-perturbed cores and suggest regimes in which island geometry, rather than collisions alone, governs radial transport.
Spectroscopic measurement campaigns are underway on the large helical device (LHD) and Heliotron J fusion devices in Japan. These campaigns aim to detect on the line shapes of hydrogen Balmer and Paschen lines a spectroscopic signature of periodic electric fields generated by gyrotrons. We present computer simulation calculations of hydrogen line shapes under plasma and periodic electric fields conditions expected along the lines of sight. Our calculations predict the emergence of replicas of the Zeeman-Stark profile located at multiples of the oscillation frequency. We also discuss the primary factors influencing the visibility of these spectral features.
In magnetized plasma environments, low-frequency electromagnetic waves such as kinetic Alfv & eacute;n waves (KAWs) play a crucial role in energy transport and plasma heating. A significant factor that has an impact on wave dynamics in such media is the polarization force, which arises from the polarization of plasma ions around negatively charged dust grains, introducing electrostatic potential gradients that significantly modify nonlinear wave behavior. This study examines the effect of polarization force on the nonlinear dynamics of KAWs in a magnetized dusty plasma composed of superthermal ions (modeled by kappa distribution), Maxwellian electrons, and negatively charged inertial dust particles. Using the standard reductive perturbation technique, we derive the Korteweg-de Vries (K-dV) and modified K-dV (mK-dV) equations to describe the evolution of small but finite amplitude KAWs. The numerical solution of the latter is employed to analyze the dynamical properties of kinetic Alfv & eacute;n solitary waves, which reveal that the polarization force leads to a noticeable increase in the amplitude of solitary waves. The results demonstrate that even weak polarization effects can play a crucial role in shaping the nonlinear features of KAWs, with implications for both space and laboratory plasma environments.
We present a thermodynamically consistent derivation of generalized Saha relations for stationary multi-temperature plasmas using a maximum entropy framework applied to systems coupled to multiple thermal reservoirs. By explicitly constraining distinct subsets of degrees of freedom, we obtain a generalized affinity relation appropriate for nonequilibrium stationary states and recover known two-temperature Saha forms as particular cases. The approach provides a transparent statistical interpretation of ionization equilibria in multi-temperature plasmas.
Neutral particles in the plasma edge of a fusion device are governed by a kinetic equation that describes how the particles are distributed in space, velocity, and time. The kinetic equation incorporates various interactions between the neutral particles and the plasma particles, such as recombination reactions, ionization reactions, and charge-exchange reactions. These so-called neutral-plasma interactions can be described mathematically by linear operators. On the other hand, there are also (elastic) self-collisions between the neutral particles themselves. These so-called neutral-neutral interactions are often neglected as they turn the kinetic equation nonlinear. For realistic fusion devices, however, these interactions can have an important influence on simulation results. Here, we describe the kinetic equation including elastic neutral-neutral collisions and derive a reduced-order model, also called a fluid model, that takes this nonlinear effect into account. The accuracy of the reduced-order model is verified numerically.
This work presents a study of the coupling between lattice ion vibrations and electron waves in magnetized piezoelectric semiconductor quantum plasmas using the quantum hydrodynamic (QHD) model. A quantum modified dispersion relation has been derived, incorporating the quantum corrections and external magnetic field. A set of nonlinear evolution equations has been established through the application of the two-time scale theory, and a soliton solution for these coupled nonlinear evolution equations has been obtained using the modified quantum Zakharov equations. The obtained solitons exhibit cusp-like solitary structures, characterized by sharp, non-differentiable peaks. The findings reveal that the amplitude of the soliton field increases significantly with particle density, while it decreases with the strength of the magnetic field and piezoelectric coupling coefficient. Inclusion of exchange and correlation potential enhances localization, producing sharper soliton profiles. These findings demonstrate that magnetic field and quantum effects provide effective control over soliton dynamics and wave transmission.
This study employed a Langmuir probe to investigate charged particle production characteristics in a cesium-free aluminum plasma grid (Al-PG) system, wherein different electric voltage differences were applied across the control grid (CG), extraction grid (EX), and analyzer limiter plate (ALP). The probe enabled measurements of current at various spatial positions and bias voltages, providing direct insight into the behavior of electrons and ions under different electrode voltage conditions. The probe current results indicate that, when comparing different CG voltages, the probe current at V (positive ion extraction) is significantly larger than that at V (negative ion extraction). Probe measurements revealed that, when the ALP voltage is varied below the probe voltage, the probe current initially increases and subsequently decreases. Under the same conditions, the probe current gradually decreases with increasing EX voltage. When a negative voltage is applied to the probe, the floating potential corresponds to the probe current peak, and this peak shifts progressively with increasing EX voltage. These probe-based observations clarify the influence of electrode potentials on charged particle transport and provide experimental guidance for optimizing cesium-free negative ion sources for advanced plasma applications.
