Nam C. Lee

Small amplitude electron-acoustic double layers and solitons in fully relativistic plasmas of two-temperature electrons

A Korteweg–de Vries (KdV) equation for fully relativistic one dimensional plasmas of arbitrarily large streaming speed and temperature is derived by using the reductive perturbation method. For plasmas with more than two species of particles, the coefficient representing quadratic nonlinearity in KdV can vanish at critical values of certain parameters. To describe the nonlinear evolution at this critical parameter, a modified KdV (mKdV) equation that contains a cubic nonlinear term is obtained. Furthermore, a mixed mKdV equation pertaining to parameters in the vicinity of the critical values is also derived, in which the quadratic and cubic nonlinearities are both present. As an illustration of the results, the mixed mKdV equation is applied to a plasma comprised of cold ions and electrons having cold (T=0) and finite temperature components. For warm temperature T⪡mec2, it is found that electron-acoustic nonlinear waves in the shape of double layer (kink) and solitary waves can exist, which have phase spe...

Ion thermal pressure effects on dust ion acoustic solitary waves in a dusty plasma obliquely propagating to an external magnetic field

Effects of the isothermal ion pressure on the dust ion acoustic solitary waves (DIASWs) in a dusty plasma, which are obliquely propagating to an external magnetic field, are investigated based on the Sagdeev potential. It is found that as the ion temperature increases the speed of the DIASW increases. The increase is more effective for a higher value of the directional cosine lz. The small amplitude solutions of the Sagdeev potential Ψ(n) expanded up to δn3 and δn4, as was done in the previous study [Choi et al., Phys. Plasmas 12, 022304 (2005)], exhibit different behaviors with respect to the change in the ion temperature. The width and height of a double layer are found to decrease with the increase in the ion temperature for both the small and the large amplitude solutions.

Derivation of electrostatic Korteweg–deVries equation in fully relativistic two-fluid plasmas

A second order Korteweg–deVries (KdV) equation that describes the evolution of nonlinear electrostatic waves in fully relativistic two-fluid plasmas is derived without any assumptions restricting the magnitudes of the flow velocity and the temperatures of each species. In the derivation, the positive and negative species of plasmas are treated with equal footings, not making any species specific assumptions. Thus, the resulting equation, which is expressed in transparent form symmetric in particle species, can be applied to any two-fluid plasmas having arbitrarily large flow velocity and ultrarelativistically high temperatures. The phase velocity of the nonlinear electrostatic waves found in this paper is shown to be related to the flow velocity and the acoustic wave velocity through the Lorentz addition law of velocities, revealing the relativistic nature of the formulation in the present study. The derived KdV equation is applied to some limiting cases, and it is shown that it can be reduced to existing...

Ponderomotive acceleration of ions by circularly polarized electromagnetic waves

The ponderomotive acceleration of multi-species ions due to circularly polarized electromagnetic waves propagating parallel to the magnetic field is calculated. When applied to a low frequency left-hand circularly polarized wave, the results show differential accelerations among the different ion species. We demonstrate that differential acceleration of ion species by the ponderomotive force can occur even in the absence of a parallel electric field component. Our work extends the results previously obtained by Li and Temerin (1993) who considered the ponderomotive acceleration due to obliquely propagating Alfven waves.

Electromagnetic solitons in fully relativistic electron-positron plasmas with finite temperature

The existence of localized structure of electromagnetic waves in relativistic electron-positron plasmas is investigated based on the pseudo-potential theory, without making any assumptions on the magnitudes of the flow velocity and temperature of the medium. The conditions for the localization of electromagnetic wave in the form of dark (dip type) soliton are found. In the small amplitude approximation, it is found that the dip becomes deeper and narrower as the temperature is raised. In low temperature T ≪ mc2, localized solution exists only if the equilibrium longitudinal fluid velocity (parallel to the direction of propagation) in the wave frame is larger than the classical thermal velocity T/m of the plasma. For ultra-relativistically high temperature T >> mc2, it is shown that dark soliton can exist if the equilibrium longitudinal velocity is larger than c/3.

Effects of charged dust particles on nonlinear ion acoustic solitary waves in a relativistic plasma

Effects of dust charges on the nonlinear ion acoustic solitary waves in a fully relativistic dusty plasma for both cases of negative and positive dusts are numerically studied based on the pseudopotential method. In the presence of dusty particles, it is found that various types of nonlinear acoustic waves exist in forms which can be viewed as sequential combinations of three kinds of elementary solitary waves: bump, dip, and kink-type solitary waves. The number and the sequence of the constituent elementary solitary waves in a given nonlinear waves depend more sensitively on dust particle density than any other parameters. For negatively charged dust particles of low density, the nonlinear wave is in the shape of bumpy solitary wave. For a somewhat higher density, the wave changes into a form which can be viewed as a combination of bump and dip-type solitary waves. As the density is increased further, a more complex nonlinear wave composed of bump, kink, and dip-type solitary waves emerges. For a much hi...

Ion-acoustic solitary waves in fully relativistic electron-ion plasmas

The possibility of ion-acoustic solitary waves in a fully relativistic plasma comprised of electrons and ions is investigated by the pseudopotential method. Applying the gas-dynamic approach developed by McKenzie [Phys. Plasmas 9, 800 (2002)] to the energy conservation laws, it is shown that, as in nonrelativistic plasmas, only compressive ion-acoustic solitary waves are possible in two-component relativistic plasmas in the case where the ions are supersonic and electrons are subsonic. It is also shown that, by introducing the relativistic ion-acoustic velocity, various existence conditions for the solitary waves in relativistic two-fluid plasmas can be cast into forms that are identical to the nonrelativistic counterparts found by the gas-dynamic approach. It can be suggested that the method presented in this study can be extended for the investigation of other kinds of electrostatic solitary waves in relativistic multicomponent plasmas.

Ponderomotive force in a moving warm two-fluid plasma

A microscopic method is used to obtain an expression for the ponderomotive force of high frequency electromagnetic waves in a warm two-fluid collisionless plasma with nonzero fluid velocity. The result contains new terms which explicitly depend on the fluid velocity and its gradients, in addition to the familiar expressions of earlier studies. It is shown that the new terms are of the same order as the Abraham force in the smallness parameter that measures the magnitude of the flow velocity of the plasma relative to the phase velocity of the wave. The stress tensor and the momentum density vector are also derived from the newly found ponderomotive force.

Derivation of nonlinear Schrödinger equation for electrostatic and electromagnetic waves in fully relativistic two-fluid plasmas by the reductive perturbation method

The reductive perturbation method is used to derive a generic form of nonlinear Schrodinger equation (NLSE) that describes the nonlinear evolution of electrostatic (ES)/electromagnetic (EM) waves in fully relativistic two-fluid plasmas. The matrix eigenvector analysis shows that there are two mutually exclusive modes of waves, each mode involving only either one of two electric potentials, A and ϕ. The general result is applied to the electromagnetic mode in electron-ion plasmas with relativistically high electron temperature (Te≫mec2). In the limit of high frequency (ck≫ωe), the NLSE predicts bump type electromagnetic soliton structures having width scaling as ∼kTe5/2. It is shown that, in electron-positron pair plasmas with high temperature, dip type electromagnetic solitons can exist. The NLSE is also applied to electrostatic (Langmuir) wave and it is shown that dip type solitons can exist if kλD≪1, where λD is the electron’s Debye length. For the kλD≫1, however, the solution is of bump type soliton wi...

Ponderomotive force in a nonisothermal plasma

In this paper a formula is derived for the ponderomotive force of electromagnetic fields in collisionless and inhomogeneous plasma when the temperature varies slowly in space and time. This result, compared to the current formula for the isothermal case, has an additional term that involves the temperature gradient. The new result is valid in anisotropic medium and better suited for application to both laboratory and space plasma situations in which the plasma is anisotropic.