Propagation characteristics of dust$-$acoustic waves in presence of a   floating cylindrical object in the DC discharge plasma
  The experimental observation of the self$-$excited dust acoustic waves (DAWs) and its propagation characteristics in the absence and presence of a floating cylindrical object are investigated. The experiments are carried out in a direct current (DC) glow discharge dusty plasma in the background of argon gas. Dust particles are found levitated at the interface of plasma and cathode sheath region. The DAWs are spontaneously excited in the dust medium and found to propagate in the direction of ion drift (along the gravity) above a threshold discharge current at lower pressure. The excitation of such low frequency wave is a result of the ion--dust streaming instability in the dust cloud. The characteristics of the propagating dust acoustic wave get modified in presence of a floating cylindrical object of radius larger than the dust Debye length. Instead of propagating in the vertical direction, the DAWs are found to propagate obliquely in presence of the floating object (kept either vertically or horizontally). In addition, horizontally aligned floating object gives rise to form a wave structure in the cone shaped dust cloud in the sheath region. The change in the propagation characteristics of DAWs are explained on the basis of modified potential (or electric field) distribution, which is a consequence of coupling of sheaths formed around the cylindrical object and the cathode. 
Mangilal Choudhary, S. Mukherjee and P. Bandyopadhyay
physics.plasm-ph