Nidhi Gaur

Localization of circularly polarized dispersive Alfvén wave and effect on solar wind turbulence

Solar wind turbulence at large inertial scales is well known for decades and believed to consist of Alfven cascade. At scales of the order of proton inertial length, Alfven cascade excites kinetic Alfven wave, fast wave, or whistler wave that carries wave energy to smaller scales. Despite supporting the kinetic Alfven wave cascade to elucidate the steeper spectra at the kinetic scales, we here present another model, the localization of longitudinally propagating dispersive Alfven wave (DAW) with finite frequency correction to illustrate the same. Inclusion of this finite frequency in Alfven wave makes them dispersive. In this approach, the dynamical equation of the wave in the presence of ponderomotive nonlinearity of the pump is obtained and then solved numerically to study the evolution of the turbulence. The ponderomotive force accounts for the coupling between the DAW and ion acoustic wave. Taking the adiabatic case, we have first studied the localization of DAW. To have the physical insight of the dynamical system, the equation is also studied semi-analytically.

Nonlinear effects of inertial Alfvén wave in low beta plasmas

This paper is devoted to the study of the nonlinear interaction and propagation of high frequency pump inertial Alfven wave (IAW) with comparatively low frequency IAW with emphasis on nonlinear effects and applications within space plasma and astrophysics for low β-plasma (β≪me/mi). We have developed a set of dimensionless equations in the presence of ponderomotive nonlinearity due to high frequency pump IAW in the dynamics of comparatively low frequency IAW. Stability analysis and numerical simulation have been carried out for the coupled system comprising of pump IAW and low frequency IAW to study the localization and turbulent spectra, applicable to auroral region. The result reveals that localized structures become more complex and intense in nature at the quasi steady state. From the obtained result, we found that the present model may be useful to study the turbulent fluctuations in accordance with the observations of FAST/THEMIS spacecraft.

Numerical simulation to study the transient self focusing of laser beam in plasma

In this paper, we present the numerical simulation for the coupled system of equations governing the dynamics of laser and Ion Acoustic Wave (IAW) in a collisionless plasma, when the coupling between the waves is through ponderomotive non-linearity. The nonlinear evolution of the laser beam is studied when the pump laser is perturbed by a periodic perturbation. By changing the perturbation wave number, we have studied its effect on the nonlinear evolution pattern of laser beam. In order to have a physical insight into the nonlinear dynamics of laser beam evolution in time and space, we have studied the laser and IAW spectra containing spatial harmonics. The magnitude of these harmonics changes with time and leads to time dependent localization of laser beam in spatial domain. The nonlinear dynamics of this localization is investigated in detail by using simulation and a semi-analytical model.

Nonlinear effects associated with kinetic Alfvén wave

The nonlinear phenomena are of striking importance in understanding the particle acceleration, heating, and turbulence in the interplanetary space. Kinetic Alfven wave (KAW) is one of the strong candidates responsible for accelerating the solar wind and powering the solar wind turbulence. Therefore, the nonlinear properties of KAW are attracting a good attention. In the present work, we have investigated the nonlinear effects associated with KAW in the solar wind plasma at around 1 A.U. The ponderomotive force of (relatively high frequency, high power) pump KAW may be used to excite the low-frequency KAW (LKAW). For this purpose, we have derived the dynamical equations to analyze the nonlinear dynamics of relatively high frequency pump KAW in the presence of LKAW perturbation. The numerical solution has been carried out for the coupled system of equations by using the pseudospectral method for space integration and finite difference method along with the predictor corrector scheme for the evolution in time. The coupled system of nonlinear dynamical equations has been analyzed to study the nonlinear effects associated with pump KAW and the resulting turbulent spectra at 1 A.U.

Linear kinetic Alfvén waves in inhomogeneous plasma: Effects of Landau damping

The turbulent spectrum of kinetic Alfven waves in inhomogeneous plasma is investigated in the presence of Landau damping. Inhomogeneities in transverse and parallel directions to the ambient magnetic field are incorporated in the dynamics. Numerical solutions of the equations governing kinetic Alfven waves in the linear regime are obtained while retaining the effects of Landau damping, which have a significant impact on the frequency spectrum generated by propagating kinetic Alfven waves. A semi-analytical model developed to elucidate the physics of this process is also described.

Nonlinear simplified model to study localization of kinetic Alfvén wave

We have presented the numerical simulation of the coupled equations governing the dynamics of kinetic Alfven wave (KAW) and ion acoustic wave in the intermediate β plasma, where β is the ratio of thermal pressure to the background magnetic pressure. We have also developed a simplified model for this nonlinear interaction using the results obtained from the simulation to understand the physics of nonlinear evolution of KAW. Localization of magnetic field intensity of KAW has been studied by means of the simplified model.

Nonlinear coupling of left and right handed circularly polarized dispersive Alfvén wave

The nonlinear phenomena are of prominent interests in understanding the particle acceleration and transportation in the interplanetary space. The ponderomotive nonlinearity causing the filamentation of the parallel propagating circularly polarized dispersive Alfven wave having a finite frequency may be one of the mechanisms that contribute to the heating of the plasmas. The contribution will be different of the left (L) handed mode, the right (R) handed mode, and the mix mode. The contribution also depends upon the finite frequency of the circularly polarized waves. In the present paper, we have investigated the effect of the nonlinear coupling of the L and R circularly polarized dispersive Alfven wave on the localized structures formation and the respective power spectra. The dynamical equations are derived in the presence of the ponderomotive nonlinearity of the L and R pumps and then studied semi-analytically as well as numerically. The ponderomotive nonlinearity accounts for the nonlinear coupling bet...

Nonlinear interaction of 3D kinetic Alfvén wave and whistler wave in solar wind plasmas

In the present work, the nonlinear evolution of 3D kinetic Alfven wave (KAW) has been investigated in solar wind plasmas. By taking the adiabatic response of background density the nonlinearity arises because of ponderomotive effects. The dynamical equations governing the dynamics of 3D KAW and whistler are obtained. We have performed the numerical simulation using pseudospectral method to study the evolution of the nonlinear localized structures of KAW in the solar wind at 1 AU. The interaction between 3D KAW and the amplification of weak whistler signal propagating in the localized structures of KAW has also been studied semi-analytically to have an insight of the localization process. The relevance of the present work to the solar wind turbulence is discussed.

Laser pulse compression and intensity enhancement in plasma

We present modeling of laser pulse compression and intensity enhancement during propagation in underdense plasma having relativistic intensity. Pulse duration shortens to less than 5 fs and 11 times intensity enhancement has been reported. Nonlinearity of plasma generates new frequency by self phase modulation which broadens the frequency spectrum of the pulse that in turn shortens the pulse duration. High intensity pulse pushes the velocity of electrons up to relativistic limit which in turn modifies the dielectric constant of plasma. Modification of the refractive index profile causes the self focusing of laser pulse. Pulse duration shortening and intensity enhancement happen in accordance with length of the plasma medium and density of the plasma.

Nonlinear effects related to circularly polarized dispersive Alfvén waves

In situ measurements of solar wind have strongly implicated its turbulent behavior. The observed power spectra report a breakpoint around length scales of the order of ion scales. As one of the responsible mechanisms for the observed steepening in power spectrum, our approach includes a right circularly polarized dispersive Alfven wave (DAW) with finite frequency correction which, when subjected to transverse collapse/filamentation instability, may possibly result in steepening of spectrum and progressive transfer of energy from larger scales to smaller scales. We have studied the nonlinear effects associated with coupling of DAW with kinetic Alfven wave in solar wind at 1 A.U. The formation of localized structures provides a clue about the emergence of turbulence. Numerical simulation is performed to study localization and power spectral density of the field and density fluctuations. The results show steeper spectrum indicating transfer of large scale turbulent energy down to small scales.