Garima Arora - Profile on Academia.edu (original) (raw)
Papers by Garima Arora
Physics of Plasmas
We report the first experimental observations of the reflection of a dust acoustic solitary wave ... more We report the first experimental observations of the reflection of a dust acoustic solitary wave from a potential barrier in a dusty plasma medium. The experiments have been carried out in an inverted P-shaped dusty plasma experimental (DPEx) device in a DC glow discharge plasma environment. The dust acoustic solitary wave is excited by modulating the plasma with a short negative Gaussian pulse that is superimposed over the discharge voltage. The solitary wave structure is seen to move toward a potential barrier, created by the sheath around a biased wire, and turn back after reflecting off the barrier. The amplitude, width, and velocity of the soliton are recorded as a function of time. The experiment is repeated for different strengths of the potential barrier and for different initial amplitudes of the solitary wave. It is found that the distance of the closest approach of the solitary wave to the center of the barrier increases with the increase in the strength of the potential barrier and with the decrease in the initial wave amplitude. An emissive probe is used to measure the sheath potential and its thickness by measuring the plasma potential profile in the axial direction over a range of resistances connected to the biased wire. A modified Korteweg-de Vries equation is derived and numerically solved to qualitatively understand the experimental findings.
Physics of Plasmas
The microstructural changes induced in a two dimensional complex plasma crystal by the movement o... more The microstructural changes induced in a two dimensional complex plasma crystal by the movement of a single extra particle existing below it are investigated experimentally using a DC glow discharge device. The finite monolayer crystal consisting of monodispersive melamine formaldehyde particles is created in the background of an Argon plasma. The crystal formation is frequently found to be accompanied by the presence of one or more slightly heavier particles suspended a little below the monolayer. The interplay of one such test particle with the crystal is investigated for two distinct cases-(i) when the particle remains confined (trapped) in the space below the crystal and (ii) when it interacts for a short while with the crystal and then moves out of the vicinity. The trapped particle orbit induces permanent structural changes in the crystal in the form of microcracks, and these changes are identified using a variety of diagnostic analyses. The cracks can be enhanced by energizing the test particle with an incident laser. The passing particle, on the other hand, induces only transient changes in the crystal from which it is able to recover and return to its initial state in a clear demonstration of the viscoelastic property of a strongly coupled system.
Physics of Plasmas
We report on experimental observations of the modifications in the propagation characteristics of... more We report on experimental observations of the modifications in the propagation characteristics of precursor solitons due to the different shapes and sizes of the object over which the dust fluid flows. The experiments have been performed in a P shaped Dusty Plasma Experimental device where dusty plasma is created in a DC glow discharge Ar plasma using kaolin particles. A floating copper wire installed radially on the cathode acts as a charged object in the plasma environment. The flow on the dust fluid is initiated by suddenly lowering the potential of the charged object from grounded potential to close to floating potential. The size (height and width) of the potential hill is then varied by drawing current from the wire through a variable resistance. With a decrease in the height of the potential hill, the amplitude, velocity, and number of excited precursor solitons are found to decrease, whereas the widths of the solitons are seen to increase. It is found that below a threshold value, these solitary waves are not excited, and the dust fluid simply flows over the hill. To examine the effect due to the shape of the potential profiles, the wire is replaced by a triangular object. Only trailing wakes are seen to be excited when the dust fluid faces the linearly increasing slope of the potential profile, whereas both solitons and wakes get excited when the object is placed with the sharp edge facing the flow. All the experimental findings qualitatively agree with numerical solutions obtained with different source terms in the forced-Korteweg-de Vries model equation.
Physics of Plasmas
A simple approach to measure the potential profile in a plasma based on the visualization of char... more A simple approach to measure the potential profile in a plasma based on the visualization of charged tracer dust particles is reported. The method is used to experimentally determine the potential around a grounded wire that is mounted on the cathode of a DC glow discharge. Argon plasma is produced in a Π-shaped Dusty Plasma Experimental (DPEx) device. The tracer particles, consisting of a few micron sized mono-dispersive Melamine Formaldehyde (MF) grains, are made to flow over the grounded wire by suitable variations in the background gas flow. By a visual tracking of the individual particle trajectories, that yields their positions and velocities at various times, the potential values at these positions are directly estimated by using energy conservation arguments. The results agree very well with conventional probe based measurements. The technique is free of some of the inherent limitations of probe based diagnostics and offers a direct and minimally invasive means of visualizing potential profiles in a plasma.
Physics of Plasmas
We present a detailed experimental study of gas flow induced motion of dust particles in a DC glo... more We present a detailed experimental study of gas flow induced motion of dust particles in a DC glow discharge plasma. The characteristics of the dust dynamics are investigated as a function of the differential gas flow rate, the background neutral pressure, the dust particle size as well as the neutral species of the gas. The experiments have been carried out in the table top Dusty Plasma Experimental (DPEx) device in which a plasma is created between a disk shaped anode and a grounded cathode in a Π-shaped pyrex glass tube. The asymptotic steady state flow velocity of the injected micron sized dust particles is found to increase with an increase of neutral flow velocity and decrease with an increase in the background pressure. Furthermore, this velocity is seen to be independent of the size of the dust particles but decreases with an increase in the mass of the background gas. A simple theoretical model, based on estimates of the various forces acting on the dust particles, is used to elucidate the role of neutrals in the flow dynamics of the dust particles. Our experiments thus provide a detailed microscopic understanding of some of the past phenomenological observations of dust flows in the DPEx device and can prove useful in future experimental implementations of dust flow experiments.
Physics of Plasmas
Dusty plasma crystals have traditionally been observed and studied in radio frequency discharge p... more Dusty plasma crystals have traditionally been observed and studied in radio frequency discharge plasmas, and their formation in a DC glow discharge plasma remains experimentally challenging. We report the first ever observation of a stable dusty plasma Coulomb crystal in the cathode sheath region of a DC glow discharge plasma. The observations are made in the dusty plasma experimental (DPEx) device where crystals of mono-disperse melamine formaldehyde grains are produced in the background of an Argon plasma. The crystalline nature of the structure is confirmed through a host of characteristic parameter estimations which includes the radial pair correlation function, Voronoi diagram, Delaunay Triangulation, the structural order parameter, the dust temperature, and the Coulomb coupling parameter. The special features of the DPEx device which permit such a crystal formation are delineated, and some principal physical features of the crystal are discussed.
Physics of Plasmas
We report the first experimental observations of the reflection of a dust acoustic solitary wave ... more We report the first experimental observations of the reflection of a dust acoustic solitary wave from a potential barrier in a dusty plasma medium. The experiments have been carried out in an inverted P-shaped dusty plasma experimental (DPEx) device in a DC glow discharge plasma environment. The dust acoustic solitary wave is excited by modulating the plasma with a short negative Gaussian pulse that is superimposed over the discharge voltage. The solitary wave structure is seen to move toward a potential barrier, created by the sheath around a biased wire, and turn back after reflecting off the barrier. The amplitude, width, and velocity of the soliton are recorded as a function of time. The experiment is repeated for different strengths of the potential barrier and for different initial amplitudes of the solitary wave. It is found that the distance of the closest approach of the solitary wave to the center of the barrier increases with the increase in the strength of the potential barrier and with the decrease in the initial wave amplitude. An emissive probe is used to measure the sheath potential and its thickness by measuring the plasma potential profile in the axial direction over a range of resistances connected to the biased wire. A modified Korteweg-de Vries equation is derived and numerically solved to qualitatively understand the experimental findings.
Physics of Plasmas
The microstructural changes induced in a two dimensional complex plasma crystal by the movement o... more The microstructural changes induced in a two dimensional complex plasma crystal by the movement of a single extra particle existing below it are investigated experimentally using a DC glow discharge device. The finite monolayer crystal consisting of monodispersive melamine formaldehyde particles is created in the background of an Argon plasma. The crystal formation is frequently found to be accompanied by the presence of one or more slightly heavier particles suspended a little below the monolayer. The interplay of one such test particle with the crystal is investigated for two distinct cases-(i) when the particle remains confined (trapped) in the space below the crystal and (ii) when it interacts for a short while with the crystal and then moves out of the vicinity. The trapped particle orbit induces permanent structural changes in the crystal in the form of microcracks, and these changes are identified using a variety of diagnostic analyses. The cracks can be enhanced by energizing the test particle with an incident laser. The passing particle, on the other hand, induces only transient changes in the crystal from which it is able to recover and return to its initial state in a clear demonstration of the viscoelastic property of a strongly coupled system.
Physics of Plasmas
We report on experimental observations of the modifications in the propagation characteristics of... more We report on experimental observations of the modifications in the propagation characteristics of precursor solitons due to the different shapes and sizes of the object over which the dust fluid flows. The experiments have been performed in a P shaped Dusty Plasma Experimental device where dusty plasma is created in a DC glow discharge Ar plasma using kaolin particles. A floating copper wire installed radially on the cathode acts as a charged object in the plasma environment. The flow on the dust fluid is initiated by suddenly lowering the potential of the charged object from grounded potential to close to floating potential. The size (height and width) of the potential hill is then varied by drawing current from the wire through a variable resistance. With a decrease in the height of the potential hill, the amplitude, velocity, and number of excited precursor solitons are found to decrease, whereas the widths of the solitons are seen to increase. It is found that below a threshold value, these solitary waves are not excited, and the dust fluid simply flows over the hill. To examine the effect due to the shape of the potential profiles, the wire is replaced by a triangular object. Only trailing wakes are seen to be excited when the dust fluid faces the linearly increasing slope of the potential profile, whereas both solitons and wakes get excited when the object is placed with the sharp edge facing the flow. All the experimental findings qualitatively agree with numerical solutions obtained with different source terms in the forced-Korteweg-de Vries model equation.
Physics of Plasmas
A simple approach to measure the potential profile in a plasma based on the visualization of char... more A simple approach to measure the potential profile in a plasma based on the visualization of charged tracer dust particles is reported. The method is used to experimentally determine the potential around a grounded wire that is mounted on the cathode of a DC glow discharge. Argon plasma is produced in a Π-shaped Dusty Plasma Experimental (DPEx) device. The tracer particles, consisting of a few micron sized mono-dispersive Melamine Formaldehyde (MF) grains, are made to flow over the grounded wire by suitable variations in the background gas flow. By a visual tracking of the individual particle trajectories, that yields their positions and velocities at various times, the potential values at these positions are directly estimated by using energy conservation arguments. The results agree very well with conventional probe based measurements. The technique is free of some of the inherent limitations of probe based diagnostics and offers a direct and minimally invasive means of visualizing potential profiles in a plasma.
Physics of Plasmas
We present a detailed experimental study of gas flow induced motion of dust particles in a DC glo... more We present a detailed experimental study of gas flow induced motion of dust particles in a DC glow discharge plasma. The characteristics of the dust dynamics are investigated as a function of the differential gas flow rate, the background neutral pressure, the dust particle size as well as the neutral species of the gas. The experiments have been carried out in the table top Dusty Plasma Experimental (DPEx) device in which a plasma is created between a disk shaped anode and a grounded cathode in a Π-shaped pyrex glass tube. The asymptotic steady state flow velocity of the injected micron sized dust particles is found to increase with an increase of neutral flow velocity and decrease with an increase in the background pressure. Furthermore, this velocity is seen to be independent of the size of the dust particles but decreases with an increase in the mass of the background gas. A simple theoretical model, based on estimates of the various forces acting on the dust particles, is used to elucidate the role of neutrals in the flow dynamics of the dust particles. Our experiments thus provide a detailed microscopic understanding of some of the past phenomenological observations of dust flows in the DPEx device and can prove useful in future experimental implementations of dust flow experiments.
Physics of Plasmas
Dusty plasma crystals have traditionally been observed and studied in radio frequency discharge p... more Dusty plasma crystals have traditionally been observed and studied in radio frequency discharge plasmas, and their formation in a DC glow discharge plasma remains experimentally challenging. We report the first ever observation of a stable dusty plasma Coulomb crystal in the cathode sheath region of a DC glow discharge plasma. The observations are made in the dusty plasma experimental (DPEx) device where crystals of mono-disperse melamine formaldehyde grains are produced in the background of an Argon plasma. The crystalline nature of the structure is confirmed through a host of characteristic parameter estimations which includes the radial pair correlation function, Voronoi diagram, Delaunay Triangulation, the structural order parameter, the dust temperature, and the Coulomb coupling parameter. The special features of the DPEx device which permit such a crystal formation are delineated, and some principal physical features of the crystal are discussed.