H. Asgari

Stochastic dynamics of charge fluctuations in dusty plasma: A non-Markovian approach

Dust particles in typical laboratory plasma become charged largely by collecting electrons and/or ions. Most of the theoretical studies in dusty plasma assume that the grain charge remains constant even though it fluctuates due to the discrete nature of the charge. The rates of ions and electrons absorption depend on the grain charge, hence its temporal evolution. Stochastic charging model based on the standard Langevin equation assumes that the underlying process is Markovian. In this work, the memory effect in dust charging dynamics is incorporated using fractional calculus formalism. The resulting fractional Langevin equation is solved to obtain the amplitude and correlation function for the dust charge fluctuation. It is shown that the effects of ion-neutral collisions can be interpreted in phenomenological sense through the nonlocal fractional order derivative.

Dust-acoustic solitary waves in dusty plasmas with non-thermal ions

Most studies on dusty plasmas have assumed that electrons and ions follow Maxwellian distributions. However, in the presence of energetic ions, the distribution of ions tends to be non-Maxwellian. It is shown here that the existence of non-thermal ions would increase the phase velocity of a dust-acoustic wave. It is also found that the change in the phase velocity profoundly affects the characteristics of a dust-acoustic solitary wave.

Dust-acoustic shock formation in adiabatic hot dusty plasmas with variable charge

Shocklike structure can be formed after a certain transient time due to the self-steepening of the negative potential. In order to have a monotonic or oscillatory shock wave, it is known that a source of dissipation is needed. In this study, we considered the variation of dust charge as a source of dissipation. By using the reductive perturbation technique, the nonlinear Burgers equation is derived and the shocklike solution is determined. The effects of dust temperature on different characteristics of dust-acoustic shock structure are discussed. It is found out that the dust thickness is not affected by dust temperature. By considering a dusty plasma system with a set of parameters, it is shown that there exists a specific dust critical temperature Tdc which gives maximum height for the dust-acoustic shock structure. The effects of the plasma species temperature on shock formation are also investigated.

Dust-acoustic shock formation in dusty plasmas with non-thermal ions

In this study, the nonlinear Burgers equation in the presence of the dust charge fluctuation is derived and the shock-like solution is determined. It is well known that in order to have a monotonic or oscillatory shock wave, a source of dissipation is needed. By using the experimental data reported in the laboratory observation of self-excited dust-acoustic shock waves [Heinrich et al., Phys. Rev. Lett. 103, 115002 (2009)], it is shown that dust charge fluctuation can be considered as a candidate for the source of dissipation needed for the dust-acoustic shock formation. By examining the effects of non-thermal ions on dust-acoustic shocks characteristics, a possible theoretical explanation for the discrepancies observed between theory and experiment is proposed.

Dust acoustic dressed soliton with dust charge fluctuations

Modeling of dust acoustic solitons observed in dusty plasma experiment [Bandyopadhyay et al., Phys. Rev. Lett. 101, 065006 (2008)] using the Korteweg-de Vries (KdV) equation showed significant discrepancies in the regime of large amplitudes (or high soliton speed). In this paper, higher order perturbation corrections to the standard KdV soliton are proposed and the resulting dressed soliton is shown to describe the experimental data better, in particular, at high soliton speed. The effects of dust charge fluctuations on the dust acoustic dressed soliton in a dusty plasma system are also investigated. The KdV equation and a linear inhomogeneous equation, governing the evolution of first and second order potentials, respectively, are derived for the system by using reductive perturbation technique. Renormalization procedure is used to obtain nonsecular solutions of these coupled equations. The characteristics of dust acoustic dressed solitons with and without dust charge fluctuations are discussed.

Non-Markovian dynamics of dust charge fluctuations in dusty plasmas

Dust charge fluctuates even in steady-state uniform plasma due to the discrete nature of the charge carriers and can be described using standard Langevin equation. In this work, two possible approaches in order to introduce the memory effect in dust charging dynamics are proposed. The first part of the paper provides the generalization form of the fluctuation-dissipation relation for non-Markovian systems based on generalized Langevin equations to determine the amplitudes of the dust charge fluctuations for two different kinds of colored noises under the assumption that the fluctuation-dissipation relation is valid. In the second part of the paper, aiming for dusty plasma system out of equilibrium, the fractionalized Langevin equation is used to derive the temporal two-point correlation function of grain charge fluctuations which is shown to be non-stationary due to the dependence on both times and not the time difference. The correlation function is used to derive the amplitude of fluctuations for early transient time.

Effects of dust pressure on the formation of solitons with dust charge fluctuation

Dusty plasmas are present in diverse systems ranging from large scale space plasmas such supernova remnant, cometary tails, asteroid zones, planetary rings, earth’s ionosphere down to small scale laboratory plasma reactors used for semiconductor wafer fabrication and particle growth. The presence of charged massive dust particles significantly influences plasma properties and also induces many new phenomena due to Coulomb interaction, wave generation and collective effects. In this work, combined effect of dust pressure and dust charge fluctuation on the formation of different types of solitons in unmagnetized dusty plasma are studied using reductive perturbative technique. The Korteweg‐de Vries equation for the un‐modulated dust acoustic solitary wave is derived. It is shown that the cold dusty plasma system with dust charge fluctuation can support solitons with both positive and negative potentials. In the absence of dust charge fluctuation, the system only allows solitary waves with negative potential....

Fractal dynamics of light scattering intensity fluctuation in disordered dusty plasmas

Dynamic light scattering (DLS) technique is a simple and yet powerful technique for characterizing particle properties and dynamics in complex liquids and gases, including dusty plasmas. Intensity fluctuation in DLS experiments often studied using correlation analysis with assumption that the fluctuation is statistically stationary. In this study, the temporal variation of the nonstationary intensity fluctuation is analyzed directly to show the existence of fractal characteristics by employing wavelet scalogram approach. Wavelet based scale decomposition approach is used to separate non-scaling background noise (without dust) from scaling intensity fluctuation from dusty plasma. The Hurst exponents for light intensity fluctuation in dusty plasma at different neutral gas pressures are determined. At low pressures, weaker damping of dust motions via collisions with neutral gases results in stronger persistent behavior in the fluctuation of DLS time series. The fractal scaling Hurst exponent is demonstrated to be useful for characterizing structural phases in complex disordered dusty plasma, especially when particle configuration or sizes are highly inhomogeneous which makes the standard pair-correlation function difficult to interpret. The results from fractal analysis are compared with alternative interpretation of disorder based on approximate entropy and particle transport using mean square displacement.

Dust Acoustic Shock Waves in Adiabatic Hot Dusty Plasmas

It is known that to have a monotonic or oscillatory shock wave a source of dissipation is needed. In this study, we considered the dust charge variation as a source of dissipation. By using the reductive perturbation technique, the nonlinear Burgers equation is derived and the shock‐like solution is determined. The effects of dust temperature on different characteristics of dust acoustic shock wave are discussed. It is found out that dust thickness is not affected by dust temperature while for every dusty plasma systems there is dust critical temperature Tdc, for which the dust acoustic shock height will be maximum.

Stochastic Dynamics of Charge Fluctuations in Dusty Plasma

Dust particles immersed in plasma acquire charge by collecting electrons and ions and also by emitting electrons. The grain charge fluctuates due to the discrete nature of the charge. The rates of ions and electrons capturing depend on the grain charge and therefore on the history of the absorption. Memory effects can be introduced into stochastic charging dynamics by generalizing the standard Langevin equation to fractional Langevin equation with shifted fractional derivative. The temporal autocorrelation function of grain charge fluctuation is derived and average amplitude of fluctuations is determined.