[en] We report the experimental excitations of nonlinear Dust Acoustic Wave (DAW) by compressing the fluid beneath the charged grounded wire in Dusty Plasma Experimental (DPEx) device. DPEx device is basically a π shaped device where a stable dust fluid of Kaoline particle is created in between the disc shaped anode and tray type grounded cathode using a DC glow discharge plasma. A floating copper wire is connected to ground potential, installed radially on the cathode, which creates a sheath around it and act as a barrier for these micro particles. The flow of the dust fluid is generated using single gas injection technique (SGI). In this technique the pressure is decreased suddenly by a mass flow meter, which creates the flow of the dust particles along the cathode whereas the negative sheath around the wire does not allow particles to flow results in the compression of the dust fluid. The compressed fluid is then released by setting the pressure to its original value, which causes the excitation of number of nonlinear structures with different phase velocities and amplitudes. Depending upon the initial amplitudes and phase velocities of the excited nonlinear waves, nonlinear waves frequently merge (collide inelastically) with each other and coalescence. The experimental details and the coalescence of these nonlinear waves will be discussed in the conference. (author)

[en] Dusty plasma supports the formation of various dynamical structures including linear and nonlinear waves, wakes, voids, etc. under different discharge conditions. Among these, void is a spectacular dust free empty domain in the dust cloud with a characteristic sharp boundary maintained by the balance between two counteracting force on the dust particles. In the present investigation, we report the formation of highly stable and reproducible void in the cathode sheath region of a specially designed DC dusty plasma experimental setup having circular disk shaped anode and a tray shaped cathode attached with a circular confinement ring. Initially, the glow discharge plasma using Argon gas at a pressure of 0.12 mbar has been produced between anode and grounded cathode by applying 280 V. Then mono-dispersed Melamine Formaldehyde (MF) dust particles having diameter of 10.66 µm are introduced into the plasma using a dust dispenser. While falling down, the dust particles get negatively charged and trapped inside the confinement rings subsequently forms stable strongly coupled coulomb crystal. Increasing the pressure, the homogeneous Coulomb crystal forms void at the center of the dust cloud. The void radius increases from 1.5 mm to 9.0 mm over the pressure range of 0.12 mbar to 0.14 mbar. Further, it is found that the inter-particle distance near the edge of the void decreases with the increase in pressure. The void diameter obtained experimentally over the discharge condition is then compared with the analytical model associated with force balance condition on the dust particles and found a good agreement between them. (author)

[en] Phase co-existence and heat transport in two dimensional systems are of always under active research in various disciplines of physics. We report an experimental observation of liquid–crystal phase co-existence in Dusty Plasma Experimental (DPEx) device. The dusty plasma system is found to be in crystal state at high neutral gas pressure and in liquid state when the pressure is reduced to a critical value. Interestingly, phase co-existence is observed in the inter-mediate pressure range in which a hot liquid state (temperature 2.5 eV) is surrounded by a cold crystal structure (0.1 eV). Crystal and liquid states are analysed through a host of structural analysis like pair correlation function, Voronoi diagram, Delaunay diagram and orientational order parameter estimation, whereas the screened Coulomb coupling parameter and dust temperature are estimated using Langevin dynamics. The heat transport length is then deduced from the temperature profile to estimate the thermal diffusivity and conductivity. This technique allows a non-invasive method to estimate the heat transport parameters unlike the experiments carried out in past. The present set of measurements shows a strong thermal gradient in the system and the estimated heat transport length is found to be less than the measurements carried out in other complex plasma experiments. Presence of few particles beneath the crystal structure is found as the possible reason of the phase co-existence which heatup the dust particles on the top by the non-reciprocal force arising from the ion wake formation mechanism. (author)