The excitation and propagation of finite-amplitude low-frequency solitary waves are investigated in an argon plasma impregnated with kaolin dust particles. A nonlinear longitudinal dust acoustic solitary wave is excited by pulse modulating the discharge voltage with a negative potential. It is found that the velocity of the solitary wave increases and the width decreases with the increase of the modulating voltage, but the product of the solitary wave amplitude and the square of the width remains nearly constant. The experimental findings are compared with analytic soliton solutions of a model Korteveg-de Vries equation.

We report experimental observations of transverse shear waves in a three-dimensional dusty plasma that is in the strongly coupled fluid regime. These spontaneous oscillations occur when the ambient neutral pressure is reduced below a threshold value and the measured dispersion characteristics of these waves are found to be in good agreement with predictions of a viscoelastic theory of dusty plasmas.

The dispersion properties of low frequency dust acoustic waves in the strong coupling regime are investigated experimentally in an argon plasma embedded with a mixture of kaolin and M nO2 dust particles. The neutral pressure is varied over a wide range to change the collisional properties of the dusty plasma. In the low collisional regime the turnover of the dispersion curve at higher wave numbers and the resultant region of ∂ω/∂k < 0 are identified as signatures of dust-dust correlations. In the high collisional regime dust neutral collisions produce a similar effect and prevent an unambiguous identification of strong coupling effects.PACS numbers: 52.25. Zb, 52.35.Fp, 52.25.Ub Dust acoustic waves (DAWs), which are the analogs of ion acoustic waves in a dusty plasma, have received a great deal of attention in recent years. Their linear and nonlinear propagation characteristics have been the subject of a large number of theoretical [1][2][3][4][5] and experimental [6][7][8][9][10][11][12] investigations. One of the important and fundamental questions related to their dispersion properties concerns the effect of dust-dust correlations. These correlation effects are deemed to be important because dusty plasmas are usually in the strongly coupled regime on account of the large amount of charge on each dust particle and its relatively low thermal velocity., the ratio of the dust Coulomb energy to the dust thermal energy is widely used as a measure of the amount of coupling. Here, Z d , d, T d , λ p denote the dust charge, the interparticle distance, the dust particle temperature and the plasma Debye length respectively. The value of this parameter, which is based on the Yukawa model, provides a broad indication of the phase of a dusty plasma i.e. whether it is in a gaseous (Γ < 1), fluid (1 < Γ < Γ c ) or solid state (Γ > Γ c ). Here Γ c is the critical value of Γ marking a phase transition point. It should be mentioned that a number of recent works [13,14] have suggested important modifications to the expression for Γ and Γ c near a critical curve. In general, when Γ >> 1 in a dusty plasma, dust-dust correlations can lead to the development of short range order in the system which keeps decaying and reforming in time. Such correlation effects can bring about significant modifications in the collective properties of the strongly coupled dusty plasma [15][16][17][18]. The influence of dust-dust correlation on DAWs was addressed in an early experiment by Pieper and Goree [8] who studied the propagation of DAWs in a dusty plasma that was close to a crystalline state. The expectation was that the linear dispersion relation of the excited compressive waves would be close to dust-lattice waves -DLWs (evidence of a strongly correlated medium) rather than that of DAWs which are typically found in a gaseous weakly coupled plasma. To their surprise they found that the dispersion properties were well explained by collisionally damped DAWs and showed no resemblance to DLWs. Their experimental findings also lent credence to t...

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