Ion Drift Waves Research Articles

Effect of Sheared Magnetic Field on E × B Drift Instability in Plasma

The influence of the magnetic shear on ion drift waves has been investigated for plasmas in the plane slab geometry with a density gradient. A differential equation is derived to describe the mode structure along the density gradient. The magnetic shear localizes the mode around a mode-rational surface, which is perpendicular to the magnetic field. The non-local growth rate turned out to be smaller as compared to the shearless one. The magnetic shear stabilizes long wavelength modes (kρi < 1 ), whereas it destabilizes, as the mode tends toward the short wavelength region, where the density gradient provides a destabilizing effect for the magnetic shear-driven resistive drift mode. However, the effect due to the collision frequency is significantly low in our analysis. The combined effects of E×B flows and the magnetic shear enhance the confinement over a narrow radial region with an internal transport barrier, where stability is attained.

Local Solvability, Blow-Up, and Hölder Regularity of Solutions to Some Cauchy Problems for Nonlinear Plasma Wave Equations: III. Cauchy Problems

Three Cauchy problems for Sobolev-type equations with a common linear part from the theory of ion acoustic and drift waves in a plasma are considered. The problems are reduced to equivalent integral equations. We prove the existence of unextendable solutions for two problems and the existence of a local-in-time solution for the third problem. For one of the problems, by applying a modified method of Kh.A. Levin, sufficient conditions for finite time blow-up of solutions are obtained and an upper bound for the solution blow-up time is found. For another problem, S.I. Pohozaev’s nonlinear capacity method is used to obtain a finite time blow-up result and two results concerning the nonexistence of even local solutions, and an upper bound for the solution blow-up time is obtained as well.

Local Solvability, Blow-up, and Hölder Regularity of Solutions to Some Cauchy Problems for Nonlinear Plasma Wave Equations: II. Potential Theory

Volume and surface potentials arising in Cauchy problems for nonlinear equations in the theory of ion acoustic and drift waves in a plasma are considered, and their properties are examined. For the volume potential, an estimate is derived, which is used to prove a Schauder-type a priori estimate and Schauder-type estimates for weighted potentials.

Field theory and a structure-preserving geometric particle-in-cell algorithm for drift wave instability and turbulence

A field theory and the associated structure-preserving geometric particle-in-cell (PIC) algorithm are developed to study low frequency electrostatic perturbations with fully kinetic ions and adiabatic electrons in magnetized plasmas. The algorithm is constructed by geometrically discretizing the field theory using discrete exterior calculus, high-order Whitney interpolation forms, and non-canonical Hamiltonian splitting method. The discretization preserves the non-canonical symplectic structure of the particle-field system, as well as the electromagnetic gauge symmetry. As a result, the algorithm is charge-conserving and possesses long-term conservation properties. Because drift wave turbulence and anomalous transport intrinsically involve multi time-scales, simulation studies using fully kinetic particles demand algorithms with long-term accuracy and fidelity. The structure-preserving geometric PIC algorithm developed adequately serves this purpose. The algorithm has been implemented in the code, tested and benchmarked using the examples of ion Bernstein waves and drift waves. We apply the algorithm to study the ion temperature gradient (ITG) instability and turbulence in a 2D slab geometry. Simulation results show that at the early stage of the turbulence, the energy diffusion is between the Bohm scaling and gyro-Bohm scaling. At later time, the observed diffusion is closer to the gyro-Bohm scaling, and density blobs generated by the rupture of unstable modes are the prominent structures of the fully developed ITG turbulence.

Theoretical Prediction of Asymmetric Instability of Drift Kinetic Alfven Waves in Anisotropic Plasmas

AbstractThe asymmetric instability of drift kinetic Alfvén waves (DKAWs) is analyzed to study the interplay between the density inhomogeneity and the temperature anisotropy, including the wave‐particle interaction and finite ion Larmor radius effects. The asymmetric behavior arises due to the opposite diamagnetic drifts of electrons and ions and quantifies the contribution of electron drift waves and ion drift waves in altering the dispersion characteristic of DKAWs. It is shown that the coupling of drift waves with kinetic Alfvén waves leads to the generation of three different frequency (i.e., higher, intermediate, and lower) modes of DKAWs. The comparison of their propagation characteristics and stability mechanisms applicable to a wide range of plasma parameters is provided. The analytical dispersion relation can be used as an improved theoretical tool for identifying the existence of DKAWs and their source region in the multisatellite observations, especially near the reconnection X‐line.

Compressive and rarefactive double layers in non-uniform plasma with q $q$ -nonextensive distributed electrons

Electrostatic solitary waves and double layers (DLs) formed by the coupled ion acoustic (IA) and drift waves have been investigated in non-uniform plasma using \(q\)-nonextensive distribution function for the electrons and assuming ions to be cold \(T_{i}< T_{e}\). It is found that both compressive and rarefactive nonlinear structures (solitary waves and DLs) are possible in such a system. The steeper gradients are supportive for compressive solitary (and double layers) and destructive for rarefactive ones. The \(q\)-nonextensivity parameter \(q\) and the magnitudes of gradient scale lengths of density and temperature have significant effects on the amplitude of the double layers (and double layers) as well as on the speed of these structures. This theoretical model is general which has been applied here to the \(F\)-region ionosphere for illustration.

Solitary structures in an inhomogeneous plasma with pseudo-potential approach

The set of nonlinear partial differential equations for the coupled ion acoustic and drift waves is reduced to the KdV equation, which is finally transformed into the form of energy integral equation of a pseudo particle in small amplitude limit. It is pointed out that this approach is convenient for choosing appropriate plasma parameters and numerically obtaining drift solitary wave profiles as compared to the solution of the KdV equation, particularly, in non-uniform plasmas. Electrons are assumed to follow the Kappa distribution function. It is found that the solitons amplitude decreases corresponding to steeper density and temperature gradients because of the restriction on the validity of local approximation. Deviation of electrons from thermal equilibrium distribution is supportive for the formation of electrostatic solitary structures by the coupled nonlinear ion acoustic and drift waves. The estimates of the width of the solitons formed by these coupled nonlinear electrostatic waves in the F-region ionosphere are found to be a few meters in agreement with the satellite observations.

Parameter-space survey of linear G-mode and interchange in extended magnetohydrodynamics

The extended magnetohydrodynamic stability of interchange modes is studied in two configurations. In slab geometry, a local dispersion relation for the gravitational interchange mode (g-mode) with three different extensions of the MHD model [Zhu et al., Phys. Rev. Lett. 101, 085005 (2008)] is analyzed. Our results delineate where drifts stablize the g-mode with gyroviscosity alone and with a two-fluid Ohm's law alone. The two-fluid Ohm's law produces an ion drift wave that interacts with the g-mode. This interaction gives rise to a second instability at finite ky. A second instability is also observed in numerical extended MHD computations of linear interchange in cylindrical screw-pinch equilibria, the second configuration. Particularly with incomplete models, this mode limits the regions of stability for physically realistic conditions. However, applying a consistent two-temperature extended MHD model that includes the diamagnetic heat flux density ( q→*) makes the onset of the second mode occur at a la...

Finite amplitude nonlinear drift waves in a spatially inhomogeneous degenerate plasma with Landau quantization and electron temperature corrections

In the present investigation, linear and nonlinear electrostatic drift waves in the presence of trapped electrons with quantizing magnetic field and finite electron temperature effects in dense plasmas have been studied. The linear dispersion relation of the ion drift wave has been derived and it has been found that the Landau quantization and finite temperature effects significantly alter the linear propagation characteristics of the wave under consideration. Employing the Sagdeev potential approach, the formation of finite amplitude drift solitary structures has been investigated in the presence of a quantizing magnetic field for both fully and partially degenerate plasmas. Both compressive and rarefactive drift solitary structures have been obtained for different values of quantizing magnetic field and finite electron temperature effects. The theoretical results obtained have been analyzed numerically for the parameters typically found in white dwarfs.

Streamers generation by small-scale drift-Alfvén waves

Excitation of streamers by modulationally unstable small-scale drift-Alfvén wave (SSDAW) is investigated. It is found that the excitation depends strongly on the propagation direction of the SSDAW, and the ion and electron diamagnetic drift waves are both unstable due to the generation of streamers. It is also shown that zonal flows can be effectively excited by the SSDAW with the propagation direction different from that for streamer excitation.

Coupled ion acoustic and drift waves in magnetized superthermal electron-positron-ion plasmas

Linear and nonlinear coupled drift-ion acoustic waves are investigated in a nonuniform magnetoplasma having kappa distributed electrons and positrons. In the linear regime, the role of kappa distribution and positron content on the dispersion relation has been highlighted; it is found that strong superthermality (low value of κ) and addition of positrons lowers the phase velocity via decreasing the fundamental scalelengths of the plasmas. In the nonlinear regime, first, coherent nonlinear structure in the form of dipoles and monopoles are obtained and the boundary conditions (boundedness) in the context of superthermality and positron concentrations are discussed. Second, in case of scalar nonlinearity, a Korteweg–de Vries-type equation is obtained, which admit solitary wave solution. It is found that both compressive and rarefactive solitons are formed in the present model. The present work may be useful to understand the low frequency electrostatic modes in inhomogeneous electron positron ion plasmas, which exist in astrophysical plasma situations such as those found in the pulsar magnetosphere.

GPS observation of continent‐size traveling TEC pulsations at the start of geomagnetic storms

AbstractWe report our experimental observation of continent‐size traveling plasma disturbances using GPS measurements of total electron content (TEC) over the North American sector. These plasma disturbances occurred at the beginning of geomagnetic storms, immediately after the shock arrived, and prior to the appearance of large‐scale traveling ionospheric disturbances (LSTIDs) from the auroral region. Specifically, these supersize TEC perturbations were observed when the interplanetary magnetic field Bz was oscillating between northward and southward directions. They were found to propagate zonally with a propagation speed of 2–3 km/s. We interpret these TEC pulsations as ion drift waves in the magnetosphere/plasmasphere that propagate azimuthally inside the GPS orbit.

Nonlinear electrostatic shock waves in inhomogeneous plasmas with nonthermal electrons

Density inhomogeneity driven linear and nonlinear ion drift waves are investigated in a plasma consisting of heavy ions and non-thermal electrons. The dissipation is introduced in the system by the ion-neutral collision frequency. The nonlinear Korteweg de Vries Burgers (KdVB) and Burgers like equations are derived in the small amplitude limit, and the solution is obtained using the tangent hyperbolic method. It is found that the system under consideration admits rarefactive shock structures. It is observed that the ion-neutral collision frequency, nonthermal electron population, inverse density inhomogeneity scalelength, and the ambient magnetic field affect the propagation characteristics of the drift shock waves. The present study may be applicable in regions of space where nonthermal electrons and heavy ions have been observed.

New formulation of the Bohm sheath criterion in terms of ion sound waves

The existing approach to formulation of the Bohm sheath criterion that determines the existence of a stationary charged near-electrode layer in plasma is critically analyzed. It is shown that the commonly accepted formulation based on the comparison of velocities of the ion drift and ion sound waves in fact compares the parameters of different plasmas and its use leads to methodologically incorrect conclusions. A new formulation of the Bohm sheath criterion is proposed, which limits the ion drift velocity from both above and below.

Electrostatic waves and instabilities in multispecies nonneutral plasmas

This paper briefly describes waves and instabilities in a multispecies nonneutral plasma that have previously been studied only in neutral plasmas: ion sound waves, drift waves, and ion temperature gradient waves. The theory of their dispersion relations and growth rates is similar to that for neutral plasmas, but results differ in several important respects. For instance, drift waves are not necessarily unstable, the instabilities generally do not cause plasma loss, and they can be controlled (e.g., turned on or off) by manipulation of density and temperature profiles using standard experimental techniques such as centrifugal separation and laser cooling/heating. This should allow precise experimental studies of instability growth and saturation.

Effects of friction on modes in collisional multicomponent plasmas

The friction in multi-component plasmas is discussed, and its effects on ion acoustic (IA) and drift waves. In the case of the IA wave it is shown that the friction between the two species has no effect on the mode in a quasi-neutral plasma. Using the Poisson equation instead of the quasi-neutrality reveals the possibility for an instability driven by the collisional energy transfer. However, the different starting temperatures of the two species imply an evolving background. It is shown that the relaxation time of the background electron-ion plasma is, in fact, always shorter than the growth rate time. Therefore the instability is unlikely to develop. The drift wave instability is also reexamined taking into account the ion response in the direction parallel to the magnetic field lines, which appears due to friction with electrons and which can not be omitted in view of the momentum conservation. A modified instability threshold is obtained. In plasmas with dominant electron collisions with neutrals, the instability threshold is shifted towards higher frequencies, compared to the case of dominant electron collisions with ions. The difference between the two cases vanishes when the ion sound response is negligible, i.e., when the instability threshold disappears, and both ions and neutrals react to the electron friction in the same manner. The results obtained here should contribute to the definite clarification of some contradictory results obtained in the past.

Electrostatic vortices in inhomogeneous pair-ion-electron and dusty plasmas

Pair-ion plasma in the presence of dust particles and electrons has been studied. A coupled linear dispersion relation containing dust ion acoustic, dust acoustic and drift waves has been found. Many standard dispersion relations have been discussed in different limits. In the nonlinear regime, the stationary solution in the form of dipolar vortices has been obtained. It is noticed that the formation of these nonlinear structures depends on the acoustic speed and diamagnetic drift speed.

Damping and drive of low-frequency modes in tokamak plasmas

The ability to predict the stability of fast-particle-driven Alfvén eigenmodes in burning fusion plasmas requires a detailed understanding of the dissipative mechanisms that damp these modes. In order to address this question, the linear gyro-kinetic, electromagnetic code LIGKA (Lauber 2003 Linear gyrokinetic description of fast particle effects on the MHD stability in tokamaks PhD Thesis Technical University München, Lauber et al 2007 J. Comp. Phys. 226 447) is employed to investigate their behaviour in realistic tokamak geometry.Recently, the model and the implementation of LIGKA were extended in order to capture rigorously the coupling of the shear Alfvén wave to the drift and sound waves. This coupling becomes important for the investigation of low-frequency modes such as the Alfvén cascade modes (AC), the beta-induced Alfvén eigenmodes (BAEs), the geodesic acoustic modes (GAMs), the energetic particle modes (EPMs) and—at even lower frequencies—the resistive wall modes (RWMs).The authors report on an effort to close the gap between high-n micro-scale turbulence codes (in their linear phase) and low-n global MHD codes. More precisely, the aim is to describe both regimes within the same framework of equations and with the same numerical implementation by improving the range of applicability and validity of LIGKA: an eigenvalue code allows one to explore both the local complex dispersion relations, e.g. kinetic Alfvén waves (electromagnetic), ion acoustic waves (electrostatic) or drift waves in realistic geometry and also their global eigenfunctions.As an application of this extension, an investigation of the kinetic RWM damping mechanisms is carried out.

Growing drift-cyclotron modes in the hot solar atmosphere

Well-known analytical results dealing with ion cyclotron and drift waves and which follow from the kinetic theory are used and the dispersion equation, which describes coupled two modes, is solved numerically. The numerical results obtained by using the values for the plasma density, magnetic field and temperature applicable to the solar corona clearly show the coupling and the instability (growing) of the two modes. The coupling happens at very short wavelengths, that are of the order of the ion gyro radius, and for characteristic scale lengths of the equilibrium density that are altitude dependent and may become of the order of only a few meters. The demonstrated instability of the two coupled modes (driven by the equilibrium density gradient) is obtained by using a rigorous kinetic theory model and for realistic parameter values. The physical mechanism which is behind the coupling is simple and is expected to take place throughout the solar atmosphere and the solar wind which contain a variety of very elongated density structures of various sizes. The mode grows on account of the density gradient, it is essentially an ion mode, and its further dissipation should result in an increased ion heating.

A Low Frequency Coherent Structure Driven by Turbulence in a Hanbit Mirror Plasma

Ion saturation currents in a Hanbit mirror plasma have been analyzed by using the wavelet bispectral method. From this bicoherence analysis, an interesting phase coherent mode has been found at a very low frequency. This mode seems to be generated by the low frequency turbulence which could be identified as either ion drift waves or interchange modes. The wave coupling process leading to this coherent structure is found to follow the resonant three-wave coupling with an exact frequency match. A brief review is given on this coherent turbulence structure in a Hanbit mirror plasma.