Effects of positron density and temperature on ion acoustic dressed solitons in an electron–positron–ion plasma

Ion acoustic dressed solitons in a three component plasma consisting of cold ions, hot electrons and positrons are studied. Using reductive perturbation method, Korteweg–de Vries (KdV) equation and a linear inhomogeneous equation, governing respectively the evolution of first and second order potentials are derived for the system. Renormalization procedure of Kodama and Taniuti is used to obtain nonsecular solutions of these coupled equations. It is found that electron–positron–ion plasma system supports only compressive solitons. For a given amplitude of soliton on increasing the positron concentration, velocity of the KdV as well as dressed soliton increases. For any arbitrary values of soliton's amplitude and positron concentration, velocity of the dressed soliton is found to be larger than that of the KdV soliton. For small amplitude of solitons, the width of KdV as well as dressed soliton decreases as positron concentration increases and width of dressed soliton is found to be larger than that of the KdV soliton. However, for a large value of soliton's amplitude as concentration of positrons increases, instead of decreasing width of dressed soliton starts to increase.     

Effect of electron–phonon interaction on the energy spectrum of a quantum antidot in the presence of a uniform strong magnetic field

We have studied the effect of electron–phonon interaction for small electron–phonon coupling on the electronic energy spectrum of an electron confined by a parabolic potential and a repulsive antidot potential in the presence of a uniform strong magnetic field and an Aharonov–Bohm flux field by using a variational procedure. We have shown that the presence of the antidot potential removes degeneracy of the Landau levels and electron–phonon interaction has nonnegligible effects on these levels.     

Modulation instability of an intense laser beam in an unmagnetized electron–positron–ion plasma

The modulation instability of an intense circularly polarized laser beam propagating in an unmagnetized, cold electron–positron–ion plasma is investigated. Adopting a generalized Karpman method, a three-dimensional nonlinear equation is shown to govern the laser field. Then the conditions for modulation instability and the temporal growth rate are obtained analytically. In order to compare with the usual electron–ion plasmas, the effect of positron concentration is considered. It is found that the increase in positron-to-electron density ratio shifts the instability region towards higher vertical wave numbers but does not cause displacement along the parallel wave number direction, and the growth rate increases as the positron-to-electron density ratio increases.     

Laser-triggered ion acceleration at moderate intensity and pulse duration

Two-dimensional particle-in-cell (PIC) simulations of laser-triggered ion acceleration in overdense plasma at moderate intensity (≃1.4×10¹⁸ W/cm²) and pulse duration (≃0.5 ps) are presented. We focus on the comparison of the efficiency of ion acceleration for normal and oblique incidence of the laser light, for backward and forward directions of ion emission, and for large and small focal spots. We discuss the correlation between the properties of accelerated ions and hot electrons, and identify the tendency of the ion spectra in the forward direction to those typical for the isothermal and adiabatic regimes of plasma expansion.     

Spin magnetosonic shock-like waves in quantum plasmas

The propagation of one-dimensional shock-like waves (SLWs) in a dissipative quantum magnetoplasma medium is studied. A quantum magnetohydrodynamic (QMHD) model is used to take into account the effects of quantum force associated with the Bohm potential and the pressure-like spin force for electrons. It is shown that the nonlinear evolution equation [Korteweg-de-Vries-Burger (KdVB)], which describes the dynamics of small but finite amplitude magnetosonic waves (MSWs) (where the dissipation is provided by the plasma resistivity) exhibits both oscillatory and monotonic shock-like perturbations (SLPs) by the effects of collective tunneling and spin alignment. Both the quantum and spin force significantly modify the shock-like structures and the strength of SLPs. The theoretical results could be of important for strongly magnetized astrophysical (e.g., pulsars, magnetars) plasmas.     

Photomagnetic effect in bilayer two-dimensional electron–hole systems

In tilted magnetic fields a bilayer electron–hole system is found to generate a photocurrent under terahertz radiation as the system is tuned to electron cyclotron resonance conditions. The photoinduced current amplitude oscillates with the magnetic field in correlation with Shubnikov–de Haas oscillations for electrons. The phenomenon is accounted for by a photomagnetic effect in electron–hole systems in the quantum Hall regime and has potentialities for terahertz detection and spectroscopy.     

Guiding of an electromagnetic pulse in a plasma immersed in combined wiggler and axial magnetic fields

We present a new plasma-based method of guiding an electromagnetic pulse. The scheme consists of an inhomogeneous magnetic field and a uniform density plasma, in contrast to existing schemes that rely on transverse plasma density gradients but need not be magnetized. The refractive index of a magnetized plasma depends on the strength and direction of the magnetic field as well as the plasma density. A guiding channel is formed by using field inhomogeneity to generate the desired transverse profile of the index of refraction. The concept is analyzed with an envelope equation and, for the specific example of a wiggler magnetic field, with a two-dimension particle-in-cell simulation. A simplified model of this scheme as producing a magnetic wall in analogy to metallic waveguides is presented, for which corresponding approximate relations for the guided mode axial wavelength and radius are derived as functions of the plasma and magnetic field parameter. These are seen to be in good agreement with particle-in-cell simulation results. Since the desired inhomogeneity of the refractive index can be made easily when the electromagnetic wave frequency is close to the cyclotron frequency, this guiding scheme is most readily applied in the microwave regime.     

Acceleration of dust grains by means of the high energy ion beam

The acceleration of charged dust grains by a high energy ion beam is investigated by obtaining the dispersion relation. The Cherenkov and cyclotron acceleration mechanisms of dust grains are compared with each other. The role of dusty plasma parameters and the magnetic field strength in the acceleration process are discussed. In addition, the stimulated waves by an ion beam in a fully magnetized dust–ion plasma are studied. It is shown that these waves are unstable at different angles with respect to the external magnetic field. It is also indicated that the growth rates increase by either increasing the ion and dust densities or decreasing the magnetic field strength. Finally, the results of our research show that the high energy ion beam can accelerate charged dust grains.     

Influence of the quantum dot shape on the determination of the electronic structure and electron decoherence

Theoretical calculations of electron–phonon scattering rates in AlGaN/GaN quantum dots (QDs) have been performed by means of effective mass approximation in the frame of finite element method. The influence of a symmetry breaking of the carrier's wave function on the electron dephasing time is investigated for various QDs shapes. In a QD system the electron energy increases when the QD shape changes from a spherical to a non-spherical form. In addition, the influence of the QD shape upon the electronic structure can be modulated by external magnetic fields. We also show that the electron–acoustic phonon scattering rates strongly depend upon both the QD shape and the applied magnetic field. As an additional parameter, the QD shape can be used to modify the electron–acoustic phonon interaction in a wide range. Moreover, the scattering rate of different transitions, such as Δm=0(1), presents distinct magnetic field dependency.     

Electromagnetic envelope solitons in magnetized plasma

A multiple scales technique is employed to solve the fluid-Maxwell equations describing a weakly nonlinear circularly polarized electromagnetic pulse in magnetized plasma. A nonlinear Schrödinger-type (NLS) equation is shown to govern the amplitude of the vector potential. The conditions for modulational instability and for the existence of various types of localized envelope modes are investigated in terms of relevant parameters. Right-hand circularly polarized (RCP) waves are shown to be modulationally unstable regardless of the value of the ambient magnetic field and propagate as bright-type solitons. The same is true for left-hand circularly polarized (LCP) waves in a weakly to moderately magnetized plasma. In other parameter regions, LCP waves are stable in strongly magnetized plasmas and may propagate as dark-type solitons (electric field holes). The evolution of envelope solitons is analyzed numerically, and it is shown that solitons propagate in magnetized plasma without any essential change in amplitude and shape.     

Ultra-low-frequency electrostatic and electromagnetic modes in self-gravitating magnetized dusty plasmas

A theoretical investigation has been made of ultra-low-frequency dust-electrostatic and dust-electromagnetic modes, propagating perpendicular to the external magnetic field, in a self-gravitating, warm, magnetized, two fluid dusty plasma system. It has been shown that the effects of self-gravitational field and dust thermal pressure significantly modify the dispersion properties of these ultra-low-frequency dust-modes. It is also found that under certain conditions, the self-gravitational effect can destabilize these ultra-low-frequency dust-electrostatic and dust-electromagnetic modes. However, the effects of the external magnetic field and dust and ion thermal pressures are found to play stabilizing role, i.e., these effects make these modes stable and counter the gravitational condensation of the dust grains. The implications of these results to some space and astrophysical dusty plasma systems, especially, to planetary ring-systems and cometary tails, are briefly mentioned. Received 16 December 1999     

Effects of Ion-to-Electron Mass Ratio on Electron Dynamics in Collisionless Magnetic Reconnection

A 2 1/2-dimensional electromagnetic particle-in-cell （PIC） simulation code is used to investigate electron behaviour in collisionless magnetic reconnectfon. The results show that the ion/electron mass ratio （mi/me） almost has no impact on the reconnection rate, however it can significantly affect electron behaviour in the diffusion region. For the case with larger mass ratio, the width of electron current sheet becomes smaller and the outflow region along the separatrix is smaller, hence the peak of the electron outflow speed is essentially larger. Density cavities and the parallel electric field E// along the separatrix can be found in the case with larger mass ratio, which may have significant influences on the acceleration and heating of the electrons near the X point.     

Nonlinear propagation of ultra-low-frequency electromagnetic modes in a magnetized dusty plasma

A theoretical investigation has been made of nonlinear propagation of ultra-low-frequency electromagnetic waves in a magnetized two fluid (negatively charged dust and positively charged ion fluids) dusty plasma. These are modified Alfvén waves for small value of and are modified magnetosonic waves for large , where is the angle between the directions of the external magnetic field and the wave propagation. A nonlinear evolution equation for the wave magnetic field, which is known as Korteweg de Vries (K-dV) equation and which admits a stationary solitary wave solution, is derived by the reductive perturbation method. The effects of external magnetic field and dust characteristics on the amplitude and the width of these solitary structures are examined. The implications of these results to some space and astrophysical plasma systems, especially to planetary ring-systems, are briefly mentioned. Received 8 July 1999 and Received in final form 11 October 1999     

Drift ion acoustic solitons in an inhomogeneous 2-D quantum magnetoplasma

Linear and nonlinear propagation characteristics of quantum drift ion acoustic waves are investigated in an inhomogeneous two-dimensional plasma employing the quantum hydrodynamic (QHD) model. In this regard, the dispersion relation of the drift ion acoustic waves is derived and limiting cases are discussed. In order to study the drift ion acoustic solitons, nonlinear quantum Kadomstev-Petviashvilli (KP) equation in an inhomogeneous quantum plasma is derived using the drift approximation. The solution of quantum KP equation using the tangent hyperbolic (tanh) method is also presented. The variation of the soliton with the quantum Bohm potential, the ratio of drift to soliton velocity in the co-moving frame, , and the increasing magnetic field are also investigated. It is found that the increasing number density decreases the amplitude of the soliton. It is also shown that the fast drift soliton (i.e., v_*>u) decreases whereas the slow drift soliton (i.e., v_*<u) increases the amplitude of the soliton. Finally, it is shown that the increasing magnetic field increases the amplitude of the quantum drift ion acoustic soliton. The stability of the quantum KP equation is also investigated. The relevance of the present investigation in dense astrophysical environments is also pointed out.     

Oscillations of Magnetized Dust Grains in Plasma Sheath with Negative Ions

The oscillations of a single magnetized dust grain in electronegative plasma sheath are investigated taking into account the existence of an external magnetic field. The influence of the content of negative ions and the magnetic field intensity on the properties of the dust vibration is analysed. The result shows that the existence of the negative ions in plasma reduces the dust oscillation frequency and drops the equilibrium position of dust, whereas the magnetic field raises the equilibrium position and also reduces the dust oscillation frequency on the condition considered.     

Nonlinear generation of zonal flows by ion-acoustic waves in a uniform magnetoplasma

It is shown that large-scale zonal flows (ZFs) can be excited by Reynolds stress of nonlinearly interacting random phase ion-acoustic waves (EIAWs) in a uniform magnetoplasma. Since ZFs are associated with poloidal sheared flows, they can tear apart short scale EIAW turbulence eddies, and hence contribute to the reduction of the cross-field turbulent transport in a magnetized plasma.     

Ion acoustic solitary waves with adiabatic ions in magnetized electron-positron-ion plasmas

Linear and nonlinear ion acoustic waves in the presence of adiabatically heated ions in magnetized electron-positron-ion plasmas are studied. The Sagdeev potential approach is employed to obtain the energy integral equation in such a mulitcomponent plasma using fluid theory. It is found that electron density humps are formed in the subsonic region in magnetized electron-positron-ion plasmas. The amplitude of electron density hump is decreased with the increase of hot ion temperature in electron-positron-ion plasmas. However, the increase in positron concentration and obliqueness of the wave increases the amplitude of nonlinear structure. The increase in positron concentration also reduces the width of the nonlinear structure in a magnetized multicomponent plasma. The numerical solutions in the form of solitary pulses are also presented for different plasma cases. The results may be applicable to astrophysical plasma situations, where magnetized electron-positron-ion plasma with hot ions can exist.     

Effects of Weak Localization and Electron–Electron Interaction in GaAs–AlGaAs Heterostructures

The influence of the processes of weak localization and electron–electron interaction in an inhomogeneous two-dimensional electron gas of a single GaAs–AlGaAs heterojunction on the low-temperature transport characteristics in the case of occupation of two quantum subbands has been investigated. The transport characteristics have been interpreted from the viewpoint of a two-layer model taking into account the existence of two bypass conduction channels corresponding to the two-dimensional and three-dimensional electron gas. Both the electrical and optical measurements point to the existence of large-scale fluctuations of the potential, which determine the dependence of the conduction and the Hall resistance of the heterostructures on the magnetic field. It has been established that the weak localization determines the charge transport in a weak magnetic field, and the electron–electron interaction determines this transport in a strong magnetic field.     

Parallel velocity shear driven electrostatic waves in a very dense nonuniform magnetoplasma

It is shown that the parallel (magnetic field-aligned) velocity shear can drive the low-frequency (in comparison with the ion gyrofrequency) electrostatic (LF-ES) waves in an ultracold super-dense nonuniform magnetoplasma. By using an electron density response arising from the balance between the electrostatic and quantum Bohm forces, as well as the ion density response deduced from the continuity and momentum equations, a wave equation for the LF-ES waves is derived. In the local approximation, a new dispersion relation is obtained by Fourier transforming the wave equation. The dispersion relation reveals an oscillatory instability of dispersive drift-like modes in super-dense quantum magnetoplasmas.