M. Bose

Spatiotemporal evolution of dielectric driven cogenerated dust density waves

An experimental observation of spatiotemporal evolution of dust density waves (DDWs) in cogenerated dusty plasma in the presence of modified field induced by glass plate is reported. Various DDWs, such as vertical, oblique, and stationary, were detected simultaneously for the first time. Evolution of spatiotemporal complexity like bifurcation in propagating wavefronts is also observed. As dust concentration reaches extremely high value, the DDW collapses. Also, the oblique and nonpropagating mode vanishes when we increase the number of glass plates, while dust particles were trapped above each glass plates showing only vertical DDWs.

Experimental observation of the behaviour of cogenerated dusty plasma using a bipolar pulsed direct current power supply

We have experimentally observed the behaviour of cogenerated dusts in unmagnetized plasma produced using a bipolar pulsed dc power supply. In this experiment, the dust particles have been generated through sputtering of graphite cathode and were stratified between two electrodes. This stratification of dust clouds has obtained at a typical range of plasma parameters, namely, 650 V (peak-to-peak) with 0.2 mbar pressure. In above condition, we detected the Taylor-like instability at the interface of two dusty clouds with different densities. A very less dust density (void like) region inside the lesser dust density portion is also noted. Again, it has been observed that a self excited dust density wave propagates towards the higher density dust fluid inside the system as well as a stationary band structure of thin multiple layers of dust particles when we apply a higher voltage (750 V peak-to-peak). The wavelength, phase velocity, and frequency of the excited wave have also been estimated.

Observation of external control and formation of a void in cogenerated dusty plasma

A void (i.e. the complete absence of macroscopic dust particles) can be generated in the bulk plasma region of a cogenerated dusty plasma with the help of a positively dc-biased ring electrode placed between two electrodes of dc discharge. This void region can then be dynamically controlled by varying the external positive bias voltage through the ring electrode.

Analysis of defects in externally driven dust-density wavefronts in cogenerated dusty plasma using the time-resolved Hilbert–Huang transform

Analysis of defects in externally driven dust-density wavefronts (DDWs) in cogenerated dusty plasma has been carried out. The DDWs are excited for threshold positive bias through another T-shaped electrode which is placed inbetween two main discharge electrodes. Spatiotemporal evolution of the DDWs reveals a wave defect and non-propagating wave mode in the DDW field. A space-time plot and the time-resolved Hilbert–Huang transform (HHT) were employed to analyze the spatiotemporal wave data at a specific location in the wave field.

Disappearance and Reappearance of Dust Particles in Cogenerated Dusty Plasma

In this unique experiment, where dust is produced in a sub-atmospheric pressure plasma formed between two parallel plate electrodes using a bipolar pulsed dc power supply as the source of power for plasma production, dust disappearance for few seconds is experimented. The plasma forming gas is a mixture of argon and acetylene. The plasma phase chemical reactions help in the formation of sub-micron dust particles that grow in size between two parallel electrodes. Using another single negative pulse, placed in between two electrodes, applied to another electrode, the dust particles can be disappeared for significant duration from the dusty plasma zone. The applied single pulse voltage is varied between 50-250 V. On the application of the pulse, in its initial phase, the dusty plasma gets disturbed and for some duration (~ few seconds) there is no light scattering observed, indicating that the dust is disappeared from the region between the electrodes. Later the plasma formation again reappears and similar structured dusty cloud is formed. The results are important as it gives an idea how to displace some unwanted dusts from our required region to another region.

Preferential energization of alpha particles in polar coronal holes at one solar radius above the photosphere

Heating of polar coronal holes during solar minimum and acceleration of the fast solar wind issuing therefrom lack comprehensive theoretical understanding. Wave particle interactions are considered to have crucial effects on the extreme properties of heavy ions in the collision-less region of the polar coronal holes. In this article, we have presented a novel sensitivity analysis to investigate plasma heating by radio waves at lower hybrid frequencies. We have employed a three fluid Maxwell model comprising electrons, protons, and alpha particles at around two solar radius heliocentric distance in the polar coronal holes and derived a dispersion relation as a thirteenth order polynomial for the frequency. Our model provides indications of preferential heating of alpha particles in comparison with protons by means of lower hybrid instabilities. We have employed the electron velocity and spatial charge distribution as our basic study tools so as to show the effects of alpha proton differential mass and differential perpendicular velocity on the preferential heating of alpha particles.

Breathing mode of dust cloud in a cogenerated dusty plasma

Recently, different types of collective processes in dusty plasmas have become prime interest amongst plasma physicists. Dust particles are present in every variety of plasmas and play a vital role in plasma crystals, semiconductor material processing, low-temperature physics, nanomaterials etc. Keeping these in mind, we have done an experiment on a cogenerated unmagnetized dusty plasma in a stainless-steel chamber between two parallel electrodes with one electrode (anode) is grounded while the other is, a graphite cathode, connected with a bipolar pulsed dc power supply. It is experimentally observed that in cogenerated unmagnetized dusty plasma the carbon dust cloud is fluctuating as a breathing mode like a heart beat mode observed in dust void, both magnetized and unmagnetized plasma. The theoretical model suggests that, in cylindrical geometry, the Bessels differential equation gives a clear cut picture for the condition of occurrence of dust rotation (m ≠ 0) or the dust breathing mode (at m = 0, where m is the order of Bessel function). Our experiment clearly shows that the whole dust cloud is fluctuating in an unmagnetized plasma not only the void fluctuation.

Modified Simon-Hoh Instability in a magnetized inhomogeneous dusty plasma

The modified Simon-Hoh Instability (MSHI) in an inhomogeneous plasma in presence of charged dust grains is investigated where the ions and dust are unmagnetized but electrons are strongly magnetized. Our dispersion relation matches exactly to the dispersion equation (18) of Sakawa et al.15, when we withdraw the contribution of dust grains from our expression. The growth rates of MSHI in presence of dust grains, shows either comparable or lower than that of dust free plasma.