Contributions to Plasma Physics最新文献

A first principle molecular dynamics (MD) simulation study on the nonlinear excitations in a quasi-localized state of a Yukawa system is presented to validate the findings of the nonlinear quasi-localized charge approximation (QLCA) model. Unlike solids or gases, quasi-localized states lack certain simplifying features, such as the ability to assume a fixed shape or volume, and they combine large displacements with strong interactions, further complicating the theoretical underpinnings of their behavior. In a recent paper [P. Kumar and D. Sharma, Physics of Plasmas 30 (2023)], the nonlinear QLCA model was applied to characterize the nonlinear excitations in a quasi-localized state of a Yukawa system, as existing continuum models have shown limited success in this regime. The simulation data presented with the screening and coupling parameters show a close agreement with the QLCA model findings. The MD simulations validate the prediction made by the QLCA model that the properties of a soliton remain unaffected by variations in the coupling parameter. The prediction made by QLCA regarding the formation of multiple solitons at higher screening parameter values has also been confirmed by the MD simulation data. The possibility of the formation of rarefactive solitons at relatively high screening parameter values within the QLCA model is also discussed.

The formation and dynamics of vertical dust chains in the radio frequency discharge plasma sheath have been investigated. The spatiotemporal evolution diagram allows the visualization of the dust chain formation process as well as the oscillation phenomenon. A clear stratification was observed, and spatially nonuniform self-organizing behavior of the dust chains, such as fractures and reconnections, was also observed, showing that the lower layers of the large-grained chains are less restricted, softer, and more prone to rearrangement. The spatial distribution characteristics of the charged particles in the sheath and the modified two-particle model, which takes into account the interparticle attraction, partially explain the mechanisms of the fracture and reorganization behavior of the dust chains.

The BBGKY hierarchy in the Wigner representation is used with an extended Singwi-Tosi-Land-Sjölander (STLS) ansatz for the two-particle distribution function [H. Kählert, G. J. Kalman, and M. Bonitz, Phys. Rev. E 90, 011101 (2014)] to study the density response function and the dispersion relation of collective modes in a strongly coupled quantum system. It is shown that the local field correction (LFC) and the dispersion relation reduce to the results of the Quasi-Localized Charge Approximation (QLCA) in the classical limit. In the quantum case, the LFC acquires a frequency-dependence, similar to the quantum version of the STLS theory. The dispersion relation is governed by a generalization of the QLCA dynamical matrix. The results are expected to be relevant for the analysis of collective modes in quantum liquids with strong correlations.

The distribution pattern of the connection length in the divertor region of Heliotron J was calculated by the field line tracing method. A multifold layer structure, characterized by the range of connection length, was revealed to interpret the response of the transport of the lower-charged impurity ions to the divertor structure. Impurity transport simulated by the EMC3-EIRENE code shows that lower-charged impurity ions tend to concentrate in the first multifold layer. This result is consistent with the line-integral extreme ultraviolet spectroscopy measurement, which implies that the impurity's response to the divertor topological structure needs to be considered in interpreting the spectroscopy result.

In this paper, the role of dust grain's gravitational force on the nonlinear dust-acoustic oscillations in non-Maxwellian dusty plasma is analyzed. It is shown that increasing the number of non-thermal ions causes the diminution of the electrostatic potential's amplitude and a reduction in the number of oscillations introduced by the gravitational force. We have also found that reducing the size of the dust grain induces qualitatively the same effects as an increase in the number of non-thermal ions and when the gravitational force is considered, the electric charge exhibits oscillatory profile and becomes less negative far away from the origin. This result may be interesting in the study of astrophysical plasmas where the electromagnetic force is smaller than the gravitational one such as in the Halley Comet.

Phase separations in strongly coupled fine particles in plasmas are discussed and two-component mixtures are simulated by molecular dynamics with the background plasma being treated as continuum. The system size of laboratory experiments is assumed and separations into phases with a common electron density of the background plasma are analyzed. Since the charge on fine particles increases approximately in proportion to the size, we expect the larger component with stronger coupling condensates from the mixture. Results expressed in terms of strengths of Coulomb coupling and screening of the larger component seem to be mostly similar to the one-component case, at least in cases where the ratio of fine particle sizes is 2, and the mixing ratio is in the range from 0.25 to 0.75.

The properties of small-amplitude solitary electron acoustic waves in a plasma where the hot electrons take regularized kappa distribution are investigated via the reductive perturbation method. It is found there only exists the sup-electron-acoustic rarefactive soliton, the electron acoustic velocity is modified by the regularized kappa distribution. The amplitude and width of the electron acoustic soliton decrease monotonously with the increase of the exponential cutoff parameter of hot electrons. But they vary with respect to the spectral index non-monotonously. As to the observed parameters in the Earth's inner magnetosphere, the speed, electric field strength, and the width of solitary electron acoustic wave are comparable with the observations.

The hydrogenic two-point model (H-2PM), an analytical model for the scrape-off layer that predicts a common electron and ion temperature and density along a flux tube from a target temperature and density, is adapted to a single-species helium (He) model, preserving the 2PM assumptions and analytical nature. Across a range of densities and heating powers, the predicted $��T_e�$ is within $��20��\mathrm{eV}�$ of upstream measurements by high-resolution Thomson scattering (HRTS) for low-confinement He plasmas performed in JET ITER-like wall (JET-ILW). For high-recycling conditions, He-2PM predictions of $��n_e�$ were within 10% of the Li-beam diagnostic measurements, excluding the near-SOL, when assuming $��Z_{\mathrm{eff}}�=�1�$, suggesting the divertor SOL was not fully ionised in the JET-ILW He plasmas.

The collisionless unmagnetized five components dusty plasmas have been considered to study the significance of the face-to-face collision of single- and multi-solitons, phase shifts due to face-to-face collision, and instability of the dust acoustic waves in Jupiter's environment. To study the consequence of face-to-face collision extended Poincaré–Lighthill–Kuo method is used to derive the two-sided nonlinear Korteweg–De Vries (KdV) equation. Besides, to investigate the dust acoustic wave's instability, the nonlinear Schrödinger equation has been derived following the procedure of Slathia et al. The multi-soliton solutions are determined by employing the Hirota bilinear method. The concerned parameters in the issue play a crucial role in the phase shift (generated by the face-to-face collision); the collisional process of single-, double-, triple-, and quadruple-soliton; and the generation of dust acoustic solitons. Furthermore, the plasma parameters are crucial in the formation of dark solitons and envelop shocks.

We report on the development and implementation of a hybrid kinetic ion–fluid electron model for electromagnetic COGENT simulations of edge plasmas. COGENT is a finite-volume gyrokinetic code that employs a locally field-aligned coordinate system combined with a mapped multi-block grid technology to handle strongly anisotropic edge plasma turbulence. The simulation model involves the long-wavelength limit of the ion gyrokinetic equation coupled to the vorticity and Ohm's law equations for the electromagnetic field perturbations. In order to handle the fast Alfvén wave time scales, an implicit-explicit time integration approach with a physics-based preconditioner is used. The model is successfully applied to the simulations of ion-scale resistive-drift ballooning turbulence in a toroidal annulus geometry. Substantial speed-up over a fully explicit time integration approach is observed.