Multi-fluid Plasma Research Articles

Beltrami fields in a three-species magnetoplasma

Nonlinear couplings between Beltrami fields (magnetic fields and ion flows) in a three-species plasmas are considered. By using a multi-fluid plasma model, a set of evolution equations for nonlinearly coupled magnetic fields and the ion vorticity is derived. Solutions of the coupled equations in the steady state are obtained and analyzed. Implications of the present investigation to macroscopic magnetic fields in the Earth's magnetotail/magnetosheath and in the heliosphere are discussed.

Origin of ELF/ULF waves triggered by positive cloud to ground lightning above mesoscale connective systems

Powerful electric currents and transient luminous events (sprites, blue jets and gigantic jets) have been detected in discharges between thunderclouds and the lower Ionosphere. The occurrence of such phenomena is strongly related to the occurrence of Ultra Low Frequency (ULF ∼ 6–50 Hz) waves and to the occurrence of positive polarity cloud‐to‐ground flashes. In the present letter, we present a novel mechanism to explain the origin and propagation of the observed ULF waves. Ionospheric clouds are composed of charged ice/smoke particulates, protons, electrons and neutrals. Our objective here is to show that such partially ionized dusty plasmas with streaming electrons in ionospheric clouds may support unstable ULF dust acoustic waves (DAWs). For our purposes, we employ a multifluid dusty plasma model and derive the dispersion relation for modified DAWs in a magnetized collisional plasma. The dispersion relation is analyzed numerically to obtain the growth rate and threshold.

Ohm’s Law in the Fast Lane: General Relativistic Charge Dynamics

Fully relativistic and causal equations for the flow of charge in curved spacetime are derived. It is believed that this is the first set of equations to be published that correctly describes the flow of charge, as well as the evolution of the electromagnetic field, in highly dynamical relativistic environments on timescales much shorter than the collapse time (GM/c3). The equations will therefore be important for correctly investigating problems such as the dynamical collapse of magnetized stellar cores to black holes and the production of jets. Both are potentially important problems in the study of gamma-ray burst engine models and in predicting the dynamical morphology of the collapse and the character of the gravitational waves generated. This system of equations, given the name of "charge dynamics," is analogous to those of hydrodynamics (which describe the flow of mass in spacetime rather than the flow of charge). The most important equation in the system is the relativistic generalized Ohm's law, which is used to compute time-dependent four-current. Unlike other equations for the current now in use, this one ensures that charge drift velocities remain less than the speed of light, takes into account the finite current rise time, is expressed in a covariant form, and is suitable for general relativistic computations in an arbitrary metric. It includes the standard known effects (Lorentz force, Hall effect, pressure effect, and resistivity) and reduces to known forms of Ohm's law in the appropriate limits. In addition, the plasma particles are allowed to have highly relativistic drift velocities, resulting in an implicit equation for the "current beaming factor" γq. It is proposed that, short of solving the multifluid plasma equations or the relativistic Boltzmann equation itself, these are the most general expressions for relativistic current flow in the one-fluid approximation, and they should be made part of the general set of equations that are solved in extreme black hole accretion and fully general numerical relativistic collapse simulations.

Self-magnetization of protoplanetary accretion disk matter

Shear-flow induced friction between neutral gas and charged particle components of different mass can yield a significant self-magnetization of matter. In this paper this process is discussed with respect to protoplanetary disk matter consisting of charged massive dust grains, neutral gas, ions and electrons. Self-consistent three-dimensional multi-fluid plasma—neutral gas—dust simulations are presented taking into account typical parameters for protoplanetary accretion disk matter like that of our early solar system. The results of the simulations show that self induced magnetic fields of 10−5 Tesla up to 10−3 Tesla can be expected in a protoplanetary accretion disk on very short time scales of a few years. Thus, shear-flow induced self-magnetization can yield a significant contribution to the magnetization of the early solar system.

Shear flow instabilities in magnetized partially ionized dense dusty plasmas

Shear flow instabilities may play an important role in the dynamics of partially ionized dusty plasmas. Within a multifluid approach the onset criteria with and without electrical resistivity are derived. Long wave length modes can be stabilized by dust–neutral gas collisional momentum transport. Self-consistent numerical simulations of the multifluid plasma dynamics illustrate the nonlinear development of vortical structures in the dust, ion, and neutral velocity as well as in the magnetic field. The unstable modes lead to a significant local amplification of the magnetic field strength. Moreover, electric current sheets form that also show vortices.

Multi-fluid MHD model and calculations of Alfvén wave spectrum and dissipation in tokamaks

The numerical method is developed for calculations of wave excitation and dissipation in Alfvén and in Ion Cyclotron Range of Frequency (ICRF) in axisymmetric tokamaks. Multi-fluid magneto-hydrodynamic plasma model is used and two-dimensional inhomogeneity of plasma parameters with arbitrary cross section of magnetic surfaces is considered. The difference scheme for the wave equation is not connected to magnetic field geometry and is suitable for the method extensions to nonlinear and three-dimensional case. Special care is taken to avoid the spectrum distortion and pollution. Relevant benchmark cases are presented. Finally, the results of numerical calculations of Alfvén wave absorption are presented for the experimental conditions foreseen for the Tokamak Chauffage Alfvén wave experiment in Brazil (TCABR) [Nucl. Fusion 30 (1996) 503]. In particular, the effect of toroidal mode coupling on the power deposition of Global Alfvén Wave (GAW) eigenmodes is demonstrated.

Nonlinearly coupled inertial Alfvén and dust acoustic waves in complex plasmas

The nonlinear coupling between finite amplitude inertial Alfvén (IA) and dust acoustic (DA) waves in a complex plasma is considered. By employing a multi-fluid dusty plasma model, which includes the effects of the ponderomotive force on the DA waves, a system of coupled equations is derived and used to study modulational instabilities of a constant amplitude IA wave. The results may have relevance to nonlinear phenomena involving IA and DA waves in low-temperature laboratory and space plasmas.

Waves in strongly magnetized relativistic plasmas: generally covariant approach.

A dispersion relation for long waves in strongly magnetized multifluid plasma in a curved spacetime is derived in a covariant form. A generally covariant form for the ray equations is obtained. The results are applicable to ray propagation in relativistic plasmas in the vicinity of strongly gravitating (black holes) or rapidly rotating (pulsars) systems.

Electric fields and currents in an island divertor configuration

One candidate for an optimized particle and energy exhaust concept in stellarators is the island divertor. Due to the special topology of such a design, its physics characteristics can be quite different from standard tokamak divertors or Limited Stellarator Plasmas. We have extended the capabilities of the two-dimensional B2-solps5.0 multifluid Scrape-Off layer plasma simulation code to handle diverted island geometries, including all relevant physics, in particular drifts and currents. We focus here on the structure of the electric potential and electric field in this island configuration. We show the establishment of potential and current flow patterns favoring density accumulation inside the island. This electric potential distribution is non-trivial and quite different from the φ=3 kT ansatz used in previous studies.

Large Amplitude Solitons and Double Layers in Multicomponent Dusty Plasmas

Supposing that the constituents of dusty plasmas are inertialess electrons, inertialess ions, and an admixture of negatively and positively charged inertial dust grains, and employing the nonlinear multi-fluid dusty plasma equations and Poisson's equation, we have derived dynamical equations for small amplitude nonlinear dust-acoustic waves, as well as the energy integral of a classical particle with a modified Sagdeev potential for large amplitude disturbances. The energy integral is analyzed both analytically and numerically to demonstrate the existence of rarefactive and compressive electrostatic potentials which travel faster than the effective dust-acoustic velocity. Compressive dust-acoustic potential exist only when there is a significant fraction of positively charged dust grains. Furthermore, the four-fluid dusty plasma system also admit double layers.

B2-EIRENE code modelling of an island divertor

The multifluid plasma scrape-off layer transport code B2 coupled to the EIRENE Monte Carlo neutral gas transport code was applied to a prototypical island divertor configuration in W7-AS. The approach predicts the accessibility of stable, layer-like energy detachment within a relatively broad density range. The island geometry with typically small field line pitch has the beneficial effects of efficient shielding of the main plasma against neutrals, and of strong momentum losses from the power carrying layer due to momentum radial transport. The latter reduces the peak power load and eases detachment. The power exhaust properties and the onset of detachment can be positively affected by the choice of the field line pitch which can be varied in W7-AS by superimposed control fields.

Instabilities in MPD thruster flows: 2. Investigation of drift and gradient driven instabilities using multi-fluid plasma models

The investigation of magnetoplasmadynamic (MPD) instabilities in connection with the performance of MPD thrusters has received increased attention for several years. A systematic investigation of macroscopic drift and gradient driven instabilities at the Institut für Raumfahrtsysteme (IRS), carried out since 1987, showed that the occurrence of acoustic wave and space charge instabilities was possible. The calculation of the linear development of instabilities using a three-fluid theory of the plasma flow will be presented. Furthermore, in order to identify the instabilities found in the three-fluid formalism, two-fluid and one-fluid models are investigated and links established. When possible, analytical approximations for the unstable roots of the linear dispersion relation are derived, giving the explicit dependence of the oscillation frequencies and growth rates on the wavevector and the various plasma parameters.

Self-organized and chaotic states in nonuniform dusty magnetoplasmas with sheared flows

It is well known that sheared plasma flows can be built up both in astrophysical environments as well as in laboratory dusty plasmas. Our objective here is to understand the coupling of velocity gradient energy to electrostatic and electromagnetic waves in nonuniform dusty magnetoplasma. For this purpose, we employ the multi-fluid dusty plasma model and derive the relevant nonlinear equations for low-frequency (in comparison with the ion gyrofrequency) waves in the presence of sheared plasma flows. Linear dispersion relations are derived and analyzed. It is found that both the electrostatic and electromagnetic waves are driven by sheared plasma flows. Furthermore, the newly derived mode coupling equations provide the possibility of self-organized and chaotic states in dusty plasmas. The results of our investigation should be helpful in understanding the properties of dusty plasma microturbulence when sources and sinks are simultaneously present.

Ionization instability of magnetized dusty gases

The ionization instability of a magnetized dusty plasma in which the neutral gas is ionized by a constant influx of energetic electrons is investigated. We have employed a multi-fluid dusty plasma model to derive dispersion relations for electrostatic dusty plasma waves in the presence of various drags (viz. frictional drag on the dust grains exerted by the neutral atoms, ion losses, ion viscosity, collisions of the ions with the neutrals, and ion losses to the walls or to the dust grains) as well as a source term which accounts for the creation of new ions through ionization of the neutral gas. The dispersion relations are analysed to demonstrate the ionization instability of long wavelength (with respect to the ion and dust gyroradii) and intermediate wavelength [shorter (longer) than the dust (ion) gyroradius] electrostatic fluctuations. The relevance of our investigation to low-temperature astrophysical and laboratory plasmas is pointed out.

Vortex formation in sheared flow driven fluctuations in nonuniform magnetized dusty gases

The linear and nonlinear properties of low-frequency (in comparison with the ion gyrofrequency) electrostatic and electromagnetic waves in nonuniform, magnetized dusty plasmas with sheared plasma flows are examined. For this purpose, the multifluid dusty plasma model is employed to derive the relevant nonlinear equations for the modified dust-convective cells as well as for the coupled dust Alfv\'en waves and dust-convective cells. In the linear limit, we obtain dispersion relations which exhibit instabilities of both the electrostatic and electromagnetic waves. In the nonlinear case, it is shown that the newly derived dynamical equations for weakly coupled waves admit various types of vortex solutions. The results can have relevance to the understanding of the salient features of nonthermal fluctuations and coherent vortex structures in nonuniform dusty magnetoplasmas such as those in the Earth's ionosphere as well as in cometary tails and interstellar clouds.

Sufficient stability criteria for fluids and plasmas

The stability of fluids and multifluid plasma equilibria is discussed in close analogy to classical mechanics: Two canonical transformations (involving the equilibrium Bernoulli function) lead to a new Hamiltonian which has the property of a general Lyapunov functional: It is constant in time within the perfect-fluid equations, its first variation is zero for a general equilibrium, and its finite second variation has a definite sign if certain inequalities are fulfilled, implying nonlinear stability.

Lyapunov stability of perfect fluid and multifluid plasma equilibria

A Lyapunov functional F for neutral fluids and for multifluid plasmas is found by a canonical transformation of the total Hamiltonian; this transformation is motivated by the requirement that all canonical variables (including Clebsch variables) should be time-independent in a perfect-fluid equilibrium. Then we find δF = 0 for such an equilibrium, and δ 2F ≥ δ 2F ∗ > 0 if the local flow velocity and the Bernoulli function of each fluid component obey certain inequalities (sufficient stability conditions). Implications for dissipative equilibria are also discussed.

Implementation into B2 of a 21‐moment description for the parallel transport

AbstractThe multifluid edge plasma code B2 is improved by implementing a new description for the parallel heat flux, thermal force, and viscous momentum flux obtained by a 21‐moment approximation. An exact transformation to a set of only two equations for each isotope is used. Hence there is only a moderate increase of the computational time. The new code provides a more accurate treatment of the parallel transport, in particular the impurity transport, valid for any impurity concentration.

Quasilinear theory for oblique low-frequency instabilities in streaming cold plasmas

A quasilinear theory is given which deals with the modification of equilibrium streaming in a multifluid cold plasma, due to the growth of unstable low-frequency waves which propagate at an angle to the external magnetic field. Expressions are obtained for the levels of magnetic field fluctuations at saturation, for both the shear and the fast Alfvén modes. If initially there is enough energy in the relative streaming, then the highest levels of turbulence occur for the fast mode propagating at a nonzero angle, rather than for the shear mode, although the growth rate for both is greatest at parallel propagation. As an example, we briefly mention the saturation of nonresonant instabilities near comets.

Mirror modes and fast magnetoacoustic waves near the magnetic pileup boundary of comet P/Halley

Large‐amplitude ultralow‐frequency wave structures observed on both sides of the magnetic pileup boundary of comet P/Halley during the flyby of the Giotto spacecraft have been analyzed using suprathermal electron density and magnetic field observations. Upstream of the boundary, electron density and magnetic field magnitude variations are anticorrelated, while in the pileup region these quantities are clearly correlated. Both in front of and behind the pileup boundary the observed waves are quasi‐perpendicular wave structures as a minimum variance analysis shows. A detailed comparison of our observations in the prepileup region with theoretical and numerical results shows that the mirror mode mode waves may have been generated by a mirror instability driven by the pressure anisotropy of the ring‐type distributions of the heavy (water group) pickup cometary ions. A mean wavelength λ1 = 2071 km is found, which is about 4 times the water group ion thermal gyroradius. For the fast mode wave structures in the pileup region, analysis of wave propagation on both sides of the pileup boundary shows that mode conversion from the mirror mode to fast mode type waves at the boundary is not a possible source mechanism. However, we show that the fast mode waves may be interpreted as stationary wave structures in a multifluid plasma. The wavelength λ2 = 1141 km derived from the observations, when using the stationary wave hypothesis, is in good agreement with the theoretical expected wave length λtheo = (774 ± 506) km computed from available ion observations.