Effect of size and shape of a moving charged object on the propagation characteristics of precursor solitons

We report on experimental observations of the modifications in the propagation characteristics of precursor solitons due to the different shapes and sizes of the object over which the dust fluid flows. The experiments have been performed in a Pi shaped Dusty Plasma Experimental device where dusty plasma is created in a DC glow discharge Ar plasma using kaolin particles. A floating copper wire installed radially on the cathode acts as a charged object in the plasma environment. The flow on the dust fluid is initiated by suddenly lowering the potential of the charged object from grounded potential to close to floating potential. The size (height and width) of the potential hill is then varied by drawing current from the wire through a variable resistance. With a decrease in the height of the potential hill, the amplitude, velocity, and number of excited precursor solitons are found to decrease, whereas the widths of the solitons are seen to increase. It is found that below a threshold value, these solitary waves are not excited, and the dust fluid simply flows over the hill. To examine the effect due to the shape of the potential profiles, the wire is replaced by a triangular object. Only trailing wakes are seen to be excited when the dust fluid faces the linearly increasing slope of the potential profile, whereas both solitons and wakes get excited when the object is placed with the sharp edge facing the flow. All the experimental findings qualitatively agree with numerical solutions obtained with different source terms in the forced-Korteweg-de Vries model equation.