Manoranjan Khan

Instability of dust acoustic wave due to nonthermal ions in a charge varying dusty plasma

The effects of nonthermal ions with excess of fast (energetic) ions on linear dust acoustic (DA) wave propagation has been investigated incorporating the dust charge variation and the isothermal dust pressure variation. It is seen that due to the dust charge variations in the presence of nonthermal ions, instead of the usual damping, there is a growth of the DA wave if the ion nonthermality parameter a>15(1+σi)/(8−72σi), σi(=Ti/Te≪1), Ti(Te) is the ion (electron) temperature, and there may occur, under certain conditions, exponentially growing mode with zero real frequency. It is also seen that in the absence of dust charge variations there also occurs a zero real frequency, exponentially growing mode if the ion nonthermality parameter a>1. In absence of dust charge variations or in the presence of adiabatic dust charge variations, finite dust temperature Td can stabilize the instability. However, in the presence of nonadiabatic dust charge variations Td cannot stabilize the instability.

Nonlinear properties of small amplitude dust ion acoustic solitary waves

In this paper some nonlinear characteristics of small amplitude dust ion acoustic solitary wave in three component dusty plasma consisting of electrons, ions, and dust grains have been studied. Simultaneously, the charge fluctuation dynamics of the dust grains under the assumption that the dust charging time scale is much smaller than the dust hydrodynamic time scale has been considered here. The ion dust collision has also been incorporated. It has been seen that a damped Korteweg–de Vries (KdV) equation governs the nonlinear dust ion acoustic wave. The damping arises due to ion dust collision, under the assumption that the ion hydrodynamical time scale is much smaller than that of the ion dust collision. Numerical investigations reveal that the dust ion acoustic wave admits only a positive potential, i.e., compressive soliton.

Effect of nonadiabatic dust charge variations on nonlinear dust acoustic waves with nonisothermal ions

The effect of nonadiabatic dust charge variation on the nonlinear dust acoustic wave in a dusty plasma consisting of warm adiabatic dust grains, isothermal electrons and nonisothermal ions have been investigated by reductive perturbation technique. It has been shown that due to the nonadiabatic dust charge variation and also for the presence of nonisothermal ions, nonlinear dust acoustic wave is governed by a modified Korteweg–de Vries Burger (mKdVB) equation. The Burger term arises due to the nonadiabatic dust charge variation, whereas the nonlinear terms are modified due the different effects of nonisothermal ions. Numerical integration of mKdVB equation shows that the nonlinear dust acoustic wave admits negative potentials with the oscillatory (dispersion dominant) or monotonic (dissipation dominant) shock transition and exhibits compressional shock wave.

Envelope ion thermal soliton in a pair-ion plasma

Pure pair-ion plasma composed of positive and negative ions with an equal charge to mass ratio has been recently created in the laboratory. The objective here is to show that ion thermal waves in a pair-ion plasma with equal ion-to-charge mass ratio can be modulated due to their coupling with quasistationary density perturbations. Modulated ion thermal waves in such a plasma can be localized and trapped in a self-created ion density hole.

Axial magnetic field generation by ponderomotive force in a laser‐produced plasma

Axial magnetic field generation in a plasma due to ponderomotive action of an obliquely incident spatially inhomogeneous laser beam is discussed. The theoretical analysis shows that the field can be excited by the collisional as well as the noncollisional processes via ponderomotive action. The collisional contribution, estimated to be in the range of kilogauss, is dominant for lower intensity (I) and shorter wavelength (λ) lasers and scales as λ−2 for both the s‐ and p‐polarized beams. The noncollisional process can excite the field to 0.5–0.6 MG for a p‐polarized intense and longer wavelength laser beam which scales as I4/3λ14/3. Faraday rotation is estimated theoretically to highlight the significance of ponderomotive effect in generating the axial field. Finally, implications of the model are discussed along with its limitations in the context of laser–plasma experiments.

Dust acoustic shock wave at high dust density

Dust acoustic (DA) shock wave at high dust density, i.e., the dust electroacoustic (DEA) or dust Coulomb (DC) shock wave has been investigated incorporating the nonadiabatic dust charge variation. The nonlinear DEA (DC) shock wave is seen to be governed by the Korteweg–de Vries Burger equation, in which the Burger term is proportional to the nonadiabaticity generated dissipation. It is seen that the shock strength decreases but after reaching minimum, it increases as the dust space charge density |qdnd| increases and the shock strength of DA wave is greater than that of DEA (DC) wave. Moreover the DEA (DC) shock width increases appreciably with increase mass mi of the ion component of the dusty plasma but for DA shock wave the effect is weak.

Small-amplitude nonlinear dust acoustic wave a magnetized dusty plasma with charge fluctuation

Some properties of nonlinear dust acoustic waves in magnetized dusty plasma with variable charges by reductive perturbation technique have been studied. The effect of adiabatic dust charge variations under the assumption that the ratio of dust charging time to the dust hydrodynamical time is very small, and the nonadiabatic dust charges variations under the assumption that the same ratio is small but finite, are also incorporated. It is seen that the magnetic field and the dust charge variations significantly modify the wave amplitude. It is also seen that in case of adiabatic charge variations, the Korteweg-de Vries (KdV) equation governs the nonlinear dust acoustic wave, whereas in case of nonadiabatic dust charge variations, the wave is governed by the KdV Burger equation. Nonadiabaticity generated anomalous dissipative effect causes generation of the dust acoustic shock wave. Numerical integration of KdV Burger equation shows that the dust acoustic wave admits oscillatory (dispersion dominant) or monotone (dissipation dominant) shock solutions depending on the magnitude of the coefficient of the Burger term.

Small Amplitude Nonlinear Dust Acoustic Wave Propagation in Saturn's F, G and E Rings

Nonlinear properties of small amplitude dust acoustic waves, incorporatingboth the ion inertial effect and dust drift effect have been studied.The effect of dust charge variation is also incorporated. It is seen thatdue to the dust charge variation, a Korteweg-de Vries (KdV) equationwith positive or negative damping term depending on the wave velocityand the ring parameters governes the nonlinear dust acoustic wave. It isseen that the damping or growth arises due to the assumption that dusthydrodynamical time scale is much smaller than that of the dust chargingscale. This assumption is valid only for planetary rings such as SaturnsF, G and E rings. Numerical investigations reveal thatall the three rings in F, G and E, dust acoustic solitary wave admits both negative and positive potentials. Instability arises from the available freeenergy of drift motion of dust grains only for the wave with wave velocity λ

Ion acoustic shock waves in a collisional dusty plasma

The effect of ion–dust collisions on small amplitude nonlinear dust ion acoustic waves has been investigated. Analytical investigation shows that propagation of the small amplitude wave is governed by Korteweg–de Vries (KdV) Burger equation. It is found that the coefficient of the Burger term is proportional to the ion viscosity, which arises through ion–dust collisions and depends on the temperatures and number densities of the electrons, ions and also on the number density of dust grains, as seen in a recent experiment (Nakamura et al.). Numerical investigations on the basis of that experimental data show that the dust–ion acoustic wave exhibits both oscillatory and monotonic shocks depending on the number density of dust particles, as observed in that experiment [Nakamura et al., Phys. Rev. Lett. 83, 1602 (1999)].

Nonlinear behavior of electron acoustic waves in an un-magnetized plasma

The nonlinear electron acoustic wave, which is found in the earth’s magnetosphere by satellite observations, is studied analytically by Lagrangian fluid description. The basic linear mode is observed in a two temperature electron species plasma where ions form stationary charge neutral background. We have obtained nonlinear description of this mode, which depends on both time and space. A possible solution shows a soliton like structure, which is localized in space, and the amplitude increases with time in the absence of dispersion. Small dispersive correction, however, shows spread of the solution in space. This method can be generalized to study the nonlinear behavior of a general class of multispecies plasma.