arXiv subjects

Sita Sundar

Publications and source records attributed to Sita Sundar.

5 recordsLinked to original sources

arXiv2019

Transverse magnetic field influence on wakefield in complex plasmas

We present the results of an investigation of the wakefield around a stationary charged grain in an external magnetic field with non-zero transverse component with respect to the ion flow direction. The impact of the orientation of magnetic field on the wake behavior in streaming complex plasmas is assessed. In contrast to previously reported significant suppression of the wake oscillations due to longitudinal magnetic field applied along flow, in the presence of transverse to flow magnetic field the wakefield exhibits a long range recurrent oscillations. Extensive investigation for a wide range of parameters reveal that in the sonic and supersonic regimes the wake has strong dependence on the direction of the magnetic field and exhibits sensitivity to even a meager deviation of magnetic field from the longitudinal orientation. The tool obtained with the study of impact of transverse component of magnetic field on the wake around grain in streaming ions can be used to potentially maneuver the grain-grain interaction to achieve controlled grain dynamics.

physics.plasm-ph↗

arXiv2019

Plasma-grains interaction mediated by streaming non-Maxwellian ions

A comprehensive parametric study of plasma-grain interaction for non-Maxwellian streaming ions in steady-state employing particle-in-cell simulations is delineated. Instead of considering the inter-grain interaction potential to be the linear sum of isolated grain potentials, we incorporate the numerical advancement developed fully for grain shielding by including nonlinear contributions from the plasma and shadowing effect. The forces acting on grains versus inter-grain distance, streaming velocity of the ions, and impact of trapped ions density (number) are characterized for non- Maxwellian ions in the presence of charge-exchange collisions. It is found that the nonlinear plasma response considerably modifies the plasma-grains interaction. Unlike the stationary plasma case, for two identical grains separated by a distance in the presence of streaming ions, the electrostatic force is neither repulsive for all grain separations nor equivalent to the force due to one isolated grain. Inadequacy of the linear response formalism in dealing with the systems having very large grain charges is also discussed. The smallest inter-grain separation for which the role of the shadow effect can be ignored is reported.

physics.plasm-ph↗

arXiv2018

Wake effects of a stationary charged grain in streaming magnetized ions

A systematic numerical study of wake potential and ion density distribution of a single grain in streaming ions under the influence of the magnetic field applied along flow is presented. Strong magnetic field introduces ion focus depletion behind grain facilitating the entrance of electrons far away in the downstream towards the grain. It is shown that the magnetic field suppresses the amplitude of wake potential and modifies the ion density distribution substantially. The wake peak potential and position characteristics, and density distribution of plasma constituents in the presence of magnetic field and charge-exchange collisions for the subsonic, sonic, and supersonic regime is also delineated. In the subsonic regime, simulations demonstrate the accumulation of ions near dust grain in the transverse direction while complete suppression of oscillations in the transverse direction takes place for sonic and subsonic regime.

physics.plasm-ph↗

arXiv2017

Dynamic anisotropy in MHD turbulence induced by mean magnetic field

In this paper, we study the development of anisotropy in strong MHD turbulence in the presence of a large scale magnetic field B 0 by analyzing the results of direct numerical simulations. Our results show that the developed anisotropy among the different components of the velocity and magnetic field is a direct outcome of the inverse cascade of energy of the perpendicular velocity components u? and a forward cascade of the energy of the parallel component u k . The inverse cascade develops for a strong B0, where the flow exhibits a strong vortical structure by the suppression of fluctuations along the magnetic field. Both the inverse and the forward cascade are examined in detail by investigating the anisotropic energy spectra, the energy fluxes, and the shell to shell energy transfers among different scales.

physics.plasm-ph↗

arXiv2017

Collision induced amplification of wakes in streaming plasmas

This work examines the formation of wake fields caused by ions streaming around a charged dust particle, using three-dimensional particle-in-cell (PIC) simulations with charge-neutral collisions included. The influence of an external driving electric field, which leads to a non-Maxwellian distribution of ions, is investigated in detail. The wake features formed for non-Maxwellian ions exhibit significant deviations from those observed within the model of a shifted Maxwellian distribution. The dependence of the peak amplitude and position of the wake potential upon the degree of collisionality is analyzed for a wide range of streaming velocities (Mach numbers). In contrast to a shifted Maxwellian distribution of ions, the drift-driven non-Maxwellian distribution exhibits an increase of the wake amplitude of the first attractive peak with increase in collisionality for high streaming velocities. At very low Mach numbers, collision-induced amplification is observed for Maxwellian as well as non-Maxwellian distributions.

physics.plasm-ph↗