Dynamics Of Plasma Particles Research Articles

Self-consistent interaction of linear gravitational and electromagnetic waves in non-magnetized plasma

This paper explores the hybridization of linear metric perturbations with linear electromagnetic (EM) perturbations in non-magnetized plasma for a general background metric. The local wave properties are derived from first principles for inhomogeneous plasma, without assuming any symmetries of the background metric. First, we derive the effective (“oscillation-center”) Hamiltonian that governs the average dynamics of plasma particles in a prescribed quasimonochromatic wave that involves metric perturbations and EM fields simultaneously. Then, using this Hamiltonian, we derive the backreaction of plasma particles on the wave itself and obtain gauge-invariant equations that describe the resulting self-consistent gravito-electromagnetic (GEM) waves in a plasma. The transverse tensor modes of gravitational waves are found to have no interaction with the plasma and the EM modes in the geometrical-optics limit. However, for longitudinal GEM modes with large values of the refraction index, the interplay between gravitational and EM interactions in plasma can have a strong effect. In particular, the dispersion relation of the Jeans mode is significantly affected by electrostatic interactions. As a spin-off, our calculation also provides an alternative resolution of the so-called Jeans swindle.

An improved analytical approach to establish the soliton solutions to the time‐fractional nonlinear evolution models

The time‐fractional Schrödinger (higher dimensional) and the Zakharov–Kuznetsov (ZK) models are the noteworthy modeling equations to interpret the propagation of signal in nonlinear optical fibers, small‐amplitude gravity waves on the surface water, high frequency acoustic waves, the interactions of small amplitude waves, the ion acoustic waves, nonlinear optics, Bose‐Einstein condensates, dynamics of plasma particles, etc. In this article, in order to develop advanced and broad‐spectrum closed‐form soliton solutions of the previously described nonlinear models, the advanced auxiliary equation approach has been put in used with reference to the beta‐derivative concept. The established soliton solutions are further comprehensive and typical and found in the form fractional, exponential, hyperbolic, and trigonometric functions and their variation. We depict 3D shape of the obtained solitons and explain the physical significance of the solitons. The accomplished solutions affirm that the method is effective and powerful and yields compatible solutions to fractional nonlinear evolution equations.

Target heating and plasma dynamics during hot magnetron sputtering of Nb

In this work, the direct current (DC) hot magnetron sputtering (HMS) of Nb has been studied and compared with the conventional cold magnetron sputtering (CMS) discharge. Particularly, these two magnetron systems were investigated in terms of current–voltage trends, behaviour of spectral lines, target temperature, and deposition rate. The current–voltage evolution showing strong variations over time in the HMS system was used to monitor the moment when thermionic emission becomes considerable. Meanwhile, thanks to the time-resolved optical emission spectroscopy (OES), the dynamics of plasma particles and the population of their electronic levels were analysed as a function of the target temperature. The target temperature was measured owing to both pyrometry and OES-based approach, i.e. by fitting an emission spectrum baseline. Finally, in the HMS configuration used in this work, the deposition rate up to 100 nm min−1 was obtained at the applied power density of 30 W cm−2, which is three times higher than the maximum power density applicable to the classical CMS system. However, with further increase in the power density, the deposition rate values were found to be saturated, which is likely caused by a significant increment in a number of thermal electrons in the discharge area.

Accuracy of the time-averaged ponderomotive approximation for laser-plasma accelerator modeling

Reliable modeling of laser-plasma accelerators, where a short and intense laser pulse propagates in an underdense plasma over long distances, is a computationally challenging task. This is due to the great disparity among the scales involved in the modeling, ranging from the micrometer scale of the laser wavelength to, for instance, the meter scale of the laser-plasma interaction length for a multi-GeV-class laser-plasma accelerator. To reduce such imbalance, the time-averaged ponderomotive approximation may be used, where the plasma particle dynamics is analytically averaged over the laser frequency, and only spatiotemporal scales associated with the laser envelope are retained in the calculations, resulting in significant computational savings. In this paper, we characterize the accuracy and robustness of the time-averaged ponderomotive approximation for a range of laser parameters of interest for present and future laser-plasma accelerators, and we show that the error introduced by the averaging process is small in all relevant cases.

Effects of Magnetic Perturbation on Reconnection and Heating in the Solar Corona

Abstract The solar corona exhibits unusually high temperatures (∼106 K) compared to the photosphere (∼5800 K). This coronal heating is one of the fundamental problems in solar physics that has yet to be resolved. Magnetic reconnection is thought to play a critical role in driving this enigmatic heating process. We address the interplay between reconnection in the solar corona and the photospheric footpoint motion. The effect of the latter is modeled to generate an external magnetic perturbation that is added to the main coronal field. Resistive magnetohydrodynamics is used where sources and sinks terms due to the perturbation are explicitly obtained in the equations. We set the perturbation to be sinusoidal in space while remaining time independent. The equations are solved using openFOAM. Our results show that magnetic reconnection with perturbation, even with a very small amplitude, leads to (1) more complex formation and evolution of X-points and plasmoids, (2) a transition from slow to fast reconnection rate, (3) a stronger increase of the temperature, and (4) a quicker formation of high-speed jets driving the hot plasma outside the simulation domain with a Mach number that is six times greater compared to the case without perturbation. Moreover, we also find that a magnetic perturbation with shorter wavelength promotes even a faster temporal evolution of the reconnection process than for the longer wavelength. Therefore, the heating and the dynamics of plasma particles in the solar corona are significantly enhanced when the reconnection process is externally disturbed by even a very small perturbation.

Long-term Correlations of Polytropic Indices with Kappa Distributions in Solar Wind Plasma near 1 au

Abstract The polytropic behavior of space plasmas defines a power law between the plasma moments during the transition of the plasma from one state to another under constant specific heat. Knowledge of the polytropic index—the power-law exponent—is essential for understanding the dynamics of plasma particles, while a full kinetic description can be established by the study of the velocity distribution of plasma particles. The particle velocities of collisionless space plasmas, such as the solar wind, follow the kappa distribution function. The kappa index, the parameter that labels and governs these distributions, is an independent variable that describes the state of plasmas and is required for a complete description of the plasma properties. Previous studies showed and demonstrated how the kappa and polytropic indices are related to each other in the presence of potential energy, and their relationship also depends on the potential degrees of freedom. This paper extends these analyses and derives the kappa and polytropic indices of the solar wind proton plasmas using Wind observations during the last two solar cycles. We examine and show the systematic long-term correlation between these indices, the magnetic field strength, and the solar activity.

Current sheets in planetary magnetospheres

In this article we aim to highlight the problems related to the structure and stability of the comparatively thin current sheets that were relatively recently discovered by space missions in the magnetospheres of the Earth and planets, as well as in the solar wind. These magnetoplasma structures are universal in collisionless cosmic plasmas and can play a key role in the processes of storage and release of energy in the space environment. The development of a self-consistent theory for these sheets in the Earth’s magnetosphere, where they were first discovered, has a long and dramatic history. Solution of the problem of the thin current sheet structure and stability become possible in the framework of a kinetic quasi-adiabatic approach required to explain their embedding and metastability properties. It was found that the structure and stability of current structures are completely determined by the nonlinear dynamics of plasma particles. Theoretical models have been developed to predict many properties of these structures and interpret many experimental observations in planetary magnetospheres and the heliosphere.

The effect of magnetic field on plasma particles in dusty plasma

In this work, we present the investigation of the formation features and internal structure of dust clouds created in plasma of glow discharge in the external magnetic field corresponding to a range of moderate and strong fields, at which the ion component is magnetized. The analysis of the plasma magnetization in the presence of dust components is carried out. We defined the values of magnetic induction at which the changes in dynamics of plasma particles in magnetic field in light inert gases are expected. The experimental setup was built in two versions. For the purpose of generating of magnetic field, the first setup was equipped with ordinary magnetic coils, and the second one included a superconducting solenoid. The discharge tubes, the main chambers where plasma was ignited and maintained in a glow discharge in lowered pressure, also have certain peculiarities, which we describe below. While using helium as a bulk gas, our study focused only on the dust trap in the region of narrowing discharge current. For neon, we used two traps: the striation trap and one just mentioned above placed in the narrowing of the discharge tube. As a result, the steady dust structures in a glow discharge under the magnetization of ions and electrons were obtained for the first time. Dust structures were rotated and tended to form a dust cluster and shell structure. A number of parameters of magnetization achieved in experiments were calculated.

Classical molecular dynamics simulations of hydrogen plasmas and development of an analytical statistical model for computational validity assessment

Classical molecular dynamics simulations of hydrogen plasmas have been performed with an emphasis on the analysis of the equilibration process. The theoretical basis of the simulation model as well as numerically relevant aspects, such as the proper choice and definition of simulation units, are discussed in detail, thus proving a thorough implementation of the computer simulation technique. Because of the lack of experimental data, molecular dynamics simulations are often considered as idealized computational experiments for benchmarking of theoretical models. However, these simulations are certainly challenging and consequently a validation procedure is also demanded. In this work we develop an analytical statistical equilibrium model for computational validity assessment of plasma particle dynamics simulations. Remarkable agreement between model and molecular dynamics results including a classical treatment of the ionization-recombination mechanism is obtained for a wide range of plasma coupling parameter values. Furthermore, the analytical model provides guidance to securely terminate simulation runs once the equilibrium stage has been reached, which in turn gives confidence in the statistics that potentially may be extracted from time histories of simulated physical quantities.

Alfvén wave coupled with flow-driven fluid instability in interpenetrating plasmas

The Alfvén wave is analyzed in case of one quasineutral plasma propagating with some constant speed v0 through another static quasineutral plasma. A dispersion equation is derived describing the Alfvén wave coupled with the flow driven mode ω=kv0 and solutions are discussed analytically and numerically. The usual solutions for two oppositely propagating Alfvén waves are substantially modified due to the flowing plasma. More profound is modification of the solution propagating in the negative direction with respect to the magnetic field and the plasma flow. For a large enough flow speed (exceeding the Alfvén speed in the static plasma), this negative solution may become non-propagating, with frequency equal to zero. In this case, it represents a spatial variation of the electromagnetic field. For greater flow speed it becomes a forward mode, and it may merge with the positive one. This merging of the two modes represents the starting point for a flow-driven instability, with two complex-conjugate solutions. The Alfvén wave in interpenetrating plasmas is thus modified and coupled with the flow-driven mode and this coupled mode is shown to be growing when the flow speed is large enough. The energy for the instability is macroscopic kinetic energy of the flowing plasma. The dynamics of plasma particles caused by such a coupled wave still remains similar to the ordinary Alfvén wave. This means that well-known stochastic heating by the Alfvén wave may work, and this should additionally support the potential role of the Alfvén wave in the coronal heating.

Kinetic description of the screening of the charge of macroparticles in a nonequilibrium plasma

A new approach has been developed for the kinetic description of the screening of the charge of macroparticles and the determination of the distribution of the effective potential in a nonequilibrium plasma. The main concept of the new approach is the description of the absorption of electrons and ions by a macroparticle through introducing effective point sinks in the kinetic equations describing the dynamics of plasma particles. With the use of this approach, explicit relations for the effective potential are derived with allowance for the collisions of electrons and ions with neutrals of the buffer gas and in the presence of an external magnetic field.

Full hamiltonian description of the interaction of particles with magnetic islands in Tokamak

In this letter, the effect of full Hamiltonian approach to plasma particle dynamics, in the presence of magnetic islands in a tokamak, is discussed. Usually, for the estimation of the diffusion of particles, the stochasticity regime of magnetic field lines is considered as sufficient. We have found that for ions in Hamiltonian description, the diffusive character of their trajectories considerably differs from the diffusive character of magnetic field lines. This then could have, among others, an influence on the performance of the ergodic divertor.

Wavelet representation of plasma particle dynamics in stationary electrostatic waves

The dynamics of plasma particles in the presence of a stationary electrostatic wave is studied by expanding the motion of each particle in powers of the wave amplitude. The coefficients of this expansion are wavelets in velocity space that gradually transform into well-behaved singular functions for t⪢to; to=(m∕k2T)1∕2. The force exerted on the plasma and the rate of kinetic energy transferred to the plasma by the wave are obtained by averaging the amplitude expansion over initial conditions. Higher-order terms show that nonlinear wave-plasma interactions are governed by a universal function M(τ) which is independent of the velocity distribution and depends only on τ=t∕tosc; tosc=(m∕kqEo)1∕2. It is found that the short-time (t≈tosc) behavior of M(τ) describing the transition between linear and nonlinear regimes is given by M(τ)=1−(τ4∕234!)+(41τ8∕278!). Also, using an implicit expansion of the particle motion, a global component Mo(τ)=(4∕τ2)J1(τ2∕2), 0⩽τ<∞, of the universal function is obtained.

Main Physical Features and Processes Determining the Performance of Stationary Plasma Thrusters

The main physical features and processes determining stationary plasma thrusters (SPTs) performance levels are considered in this paper, including ionization processes and ion dynamics in the accelerating channel, as well as the results of SPT design optimization, factors determining SPT lifetime, and the possibilities of simulating the plasma particle dynamics in the accelerating channel and in its plume.

Particle dynamics in low frequency electromagnetic waves in inhomogeneous plasma

Phase space dynamics of plasma particles in low frequency (ω≪ωci) electromagnetic waves in a low beta inhomogeneous plasma is obtained including the effects of finite ion gyroradius, bounce resonance, and gradient B and diamagnetic drifts. Application of the results to particle flux observations in the magnetosphere is discussed.

Radio emission from an intense electromagnetic beam-plasma system

Interaction of a high-intensity and low-frequency electromagnetic beam with a plasma is investigated. The dynamics of plasma particles under this strong electromagnetic field is calculated without using the perturbation procedures. The intensity of radio radiation from such particles is calculated and the results are applied to the extragalactic radio sources.