Spatiotemporal evolution of a self-excited dust density wave in a nanodusty plasma under strong Havnes effect Bidyut Chutia, T. Deka, Y. Bailung, D. Sharma, S. K. Sharma, H. Bailung Physics of Plasmas, 2021 A broad-spectrum self-excited dust density wave is experimentally studied in a vertically extended nanodusty plasma consisting of in situ grown carbonaceous nanometer sized particles. The nanodusty plasma having high particle density (of the order of 1012–1013 m−3) is created with vertical extension up to (40±0.1) cm and radial extension up to (5±0.1) cm. The propagation of the self-excited dust density wave under strong Havnes effect is examined over a large axial distance (19±0.1) cm. Time-resolved Hilbert transformation and Fast Fourier transformation techniques are used to study the spatiotemporal evolution of frequency and wavenumbers along three directions from the dust void, viz., axial, radial, and oblique. The propagation is found to be inhomogeneous throughout the dust cloud. The phase velocity of the wave is estimated to be quite low and decreasing along the direction of propagation. This effect is attributed to the strong reduction of particle charge due to a high Havnes parameter along the propagation direction. By the estimation of average particle charge, ion density, and the finite electric field throughout the nanodust cloud, a quantitative analysis of the void formation in nanodusty plasma is presented. New insights are also made regarding wave merging phenomena using time-resolved Hilbert transformation.
A nanodusty plasma experiment to create extended dust clouds using reactive argon acetylene plasmas Bidyut Chutia, T. Deka, Y. Bailung, S. K. Sharma, H. Bailung Physics of Plasmas, 2021 A large volume 3D dust cloud containing in situ grown nanometer-sized particles is produced in a newly developed versatile table-top experimental device. Carbonaceous nanoparticles having almost uniform size throughout the dust cloud are grown using capacitively coupled rf discharge in Ar–C2H2 gas mixture with a low precursor gas flow rate (∼2 sccm) and minimal rf power (∼1 W). The vertical and radial extensions of the dust cloud are 40 cm and 5 cm, respectively. The pure Ar plasma in the setup is characterized by measuring the discharge parameters as well as plasma parameters under different discharge conditions. The average particle size and its temporal growth profile are determined by analyzing the scanning electron microscope images of the particles. The dust density measured using the laser extinction method is found to be of the order of 1016–1012 m−3 for the discharge duration of 2–10 min. A spontaneous dust density wave is also observed in the dust cloud.
Vortex formation in a strongly coupled dusty plasma flow past an obstacle Yoshiko Bailung, Bidyut Chutia, T. Deka, A. Boruah, Sumita K. Sharma, Sandeep Kumar, Joyanti Chutia, Y. Nakamura, H. Bailung Physics of Plasmas, 2020 A pair of counter-rotating symmetric vortices has been observed in the wake behind a stationary obstacle (dust void) in a flowing dusty plasma. A strongly coupled dusty plasma flow with controllable velocity is generated and directed toward the void in a novel experiment. In the unsteady laminar flow regime, the curl of the fluid flow velocity along the boundary layer of the void generates the vortex pair behind the void. Particle image velocimetry analysis of high speed image data clearly depicts the flow pattern and the vorticities. The shear viscosity of the dusty plasma fluid along with the experimental parameters is considered to obtain the Reynolds number range for the evolution of the vortices. Molecular dynamics simulation is also performed to support the experimental observation.
Suppression of a spontaneous dust density wave by modulation of ion streaming Tonuj DEKA, Bidyut CHUTIA, Y BAILUNG, S K SHARMA, H BAILUNG Plasma Science and Technology, 2020 Synchronization of a self-excited dust density wave has been experimentally investigated in a strongly coupled dusty plasma. A dust density wave of frequency ∼78 Hz is spontaneously generated from the dust void boundary due to the ion streaming instability. The electric field in the dust void region is measured, and the electric field force and ion drag force on the dust particles at the void boundary are estimated to explain the mechanism of spontaneous dust density wave excitation. Synchronization occurring through the suppression mechanism is observed by modulating the ion streaming by applying an external sinusoidal signal to the dust void. At sufficiently high modulation amplitude, the onset of period-doubling bifurcation is observed. Fast Fourier transform spectral analysis is done using time-series data obtained from high-speed video imaging. The van der Pol equation with a force term is used to correlate the observed suppression phenomena.
Characteristics of dust voids in a strongly coupled laboratory dusty plasma Yoshiko Bailung, T. Deka, A. Boruah, S. K. Sharma, A. R. Pal, Joyanti Chutia, H. Bailung Physics of Plasmas, 2018 A void is produced in a strongly coupled dusty plasma by inserting a cylindrical pin (∼0.1 mm diameter) into a radiofrequency discharge argon plasma. The pin is biased externally below the plasma potential to generate the dust void. The Debye sheath model is used to obtain the sheath potential profile and hence to estimate the electric field around the pin. The electric field force and the ion drag force on the dust particles are estimated and their balance accounts well for the maintenance of the size of the void. The effects of neutral density as well as dust density on the void size are studied.
Observation of self-excited dust acoustic wave in dusty plasma with nanometer size dust grains Tonuj Deka, A. Boruah, S. K. Sharma, H. Bailung Physics of Plasmas, 2017 Dusty plasma with a nanometer size dust grain is produced by externally injecting carbon nanopowder into a radio frequency discharge argon plasma. A self-excited dust acoustic wave with a characteristic frequency of ∼100 Hz is observed in the dust cloud. The average dust charge is estimated from the Orbital Motion Limited theory using experimentally measured parameters. The measured wave parameters are used to determine dusty plasma parameters such as dust density and average inter particle distance. The screening parameter and the coupling strength of the dusty plasma indicate that the system is very close to the strongly coupled state.
