  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.
