Experimental investigation of flow induced vortices in a dusty plasma

We report experimental observations of the formation of dust vortices in a flowing dusty plasma. The experiments are performed in an inverted Pi-shaped dusty plasma experimental (DPEx) device, and the dusty plasma is created in a DC glow discharge Argon plasma using micron-sized Kaolin dust particles. A pulsed gas valve with 0.5 mm orifice is installed axially in the device to initiate a directional motion of the dust particles in a particular dust layer. The average velocity of the dust particles is tuned by altering the difference of the background plasma pressure and the inlet pressure of the pulsed valve. It is found that the velocity of the dust layer increases with an increase in the inlet gas pressure for a given background

pressure. The shear generated at the interface of the moving and the stationary layers leads to the formation of vortices when the inlet gas pressure crosses a threshold value. It is observed that the vortex size becomes smaller with an increase in the gas pressure of the pulsed valve. The shear velocity increases even further when the stationary layer is

made to flow in an opposite direction. It is noticed that vortices with smaller diameters become more prominent in such a case. The magnitude of vorticity is found to be maximum when both the dust layers move in opposite directions.