Collective dynamics of large aspect ratio dusty plasma in an inhomogeneous plasma background: Formation of the co--rotating vortex series

TL;DR

This study investigates the collective behavior of large aspect ratio dusty plasma under various discharge conditions, revealing the formation of co-rotating vortex series driven by plasma inhomogeneity and charge gradients.

Contribution

It introduces a novel experimental technique for confining dust grains and demonstrates the formation of co-rotating vortices in dusty plasma, aligning with theoretical models.

Findings

Vortices form above a threshold dust cloud width.

Co-rotating vortices are driven by charge gradients due to plasma inhomogeneity.

Experimental results agree with theoretical predictions.

Abstract

In this paper, the collective dynamics of the large aspect ratio dusty plasma is studied over a wide range of discharge parameters. An inductively coupled diffused plasma, which creates an electrostatic trap to confine the negatively charged grains, is used to form a large volume (or large aspect ratio) dusty plasma at low pressure. For introducing the dust grains into the potential well, a unique technique using a secondary DC glow discharge plasma is employed. The dust dynamics is recorded in a 2-dimension (2D) plane at a given axial location. The dust fluid exhibits wave like behavior at low pressure (p < 0.06 mbar) and high rf power (P > 3 W). The mixed motion, waves and vortices, are observed at an intermediate gas pressure(p = 0.08 mbar) and low power (P < 3 W). Above the threshold value of gas pressure (p > 0.1 mbar), the clockwise and anti-clockwise co-rotating vortex series are observed on the edges of the dust cloud, whereas the particles in central region show the random motion. These vortices are only observed above a threshold width of the dust cloud. The streaming ions are considered the available free energy source to excite the waves in dust grain medium. The occurrence of the co-rotating vortices is understood on the basis of the charge gradient of dust particles which is orthogonal to the gravity. The charge gradient is a consequence of the plasma inhomogeneity from the central region to the outer edge of dust fluid. Since, a vortex has the characteristic size in the dissipative medium; therefore, a series of the co-rotating vortex on the both sides of dusty plasma is observed. The experimental results on the vortex formation and its multiplicity are compared to an available theoretical model and are found to be in close agreement.