Bulletin of the American Physical Society
63rd Annual Gaseous Electronics Conference and 7th International Conference on Reactive Plasmas
Volume 55, Number 7
Monday–Friday, October 4–8, 2010; Paris, France
Session MR3: Dusty Plasmas I |
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Chair: Steven Girshick, University of Minnesota Room: Petit Amphitheatre |
Thursday, October 7, 2010 8:30AM - 8:45AM |
MR3.00001: New mechanisms of rotation of 3D plasma clusters L. Woerner, V. Nosenko, S.K. Zhdanov, A.V. Ivlev, C. Raeth, H.M. Thomas, M. Kroll, J. Schablinski, D. Block, A. Piel, G.E. Morfill Dust grains introduced into a plasma can charge up and arrange in ordered systems. A plasma crystal can be made to rotate by applying a rotating electric field. We report on the behavior of 3D dust clouds suspended by thermophoretic levitation in a four-electrode box placed in rf discharge. The speed of cluster rotation depends on the frequency of the applied sinusoidal voltage. Clusters always rotate in the direction of the electric field, which is consistent with the ion-drag force mechanism. Additional tests indicate that the delayed-charging mechanism might play a role. The angular speed of the particle rotation in the cluster increases with increasing height. Possible causes of this include the height dependence of the ion drag force and plasma screening. To study the full 3D dynamics of a cluster additional experiments using the laser holography imaging method were performed at the University of Kiel. In these experiments, 3D plasma crystals also rotated in response to rotating electric fields. [Preview Abstract] |
Thursday, October 7, 2010 8:45AM - 9:00AM |
MR3.00002: Afterglow in high frequency capacitive discharge with/without nanoparticles Irina Schweigert After switching off the plasma of the high frequency discharge decays due to ambipolar diffusion process. The characteristic time of plasma relaxation is different for pristine and dusty plasma since the effective surface for electrons and ions loss in dusty plasma is substantially larger. Additionally the negatively charged massive nanoparticles visibly affect the diffusion process. In this work we study the plasma relaxation in discharge afterglow with using PIC MCC method for different gas pressures. The simulations are performed for pure argon plasma and for plasma with a monodisperse ensemble of nanoparticles ranging from 40 to 200 nm in size. The charge of nanoparticles is calculated from the balance equation for electron and ion flux on the nanoparticle surface. The charge of nanoparticles varies over the discharge volume and decreases with time. It is shown that the characteristic time of plasma decay becomes less with decreasing gas pressure and the presence of nanoparticles essentially enhances the rate of plasma decay. [Preview Abstract] |
Thursday, October 7, 2010 9:00AM - 9:15AM |
MR3.00003: Plasma characterization during dust formation in a N2 CH4 CCP RF discharge Ga\"etan Wattieaux, Ella Sciamma-O'Brien, Johannes Berndt, Nathalie Carrasco, La\"Ifa Boufendi, Guy Cernogora A capacitively coupled radiofrequency discharge in methane nitrogen (N$_{2}$-CH$_{4})$ gas mixture is used to simulate the formation of solid aerosols of Titan's atmosphere. When dust particles are formed in this kind of discharges, they induce drastic changes in the discharge and plasmas characteristics such as: electron temperature and density, gas composition, self bias etc. In the present work, electron density is measured thanks to resonant microwave cavity method. The time evolution of electron temperature is evaluated using Optical Emission Spectroscopy through an Argon line. In-situ mass spectrometry is used to follow the evolution of the gas composition. Correlation between the results given by all these diagnostic tools shows that the dust particles growth kinetics takes few tens of seconds. This can be clearly observed through the time evolution of the methane consumption and the electron density decay. This decay is balanced by an increase of the electron temperature. [Preview Abstract] |
Thursday, October 7, 2010 9:15AM - 9:30AM |
MR3.00004: Melting scenario for two-dimensional plasma crystals V. Nosenko, S.K. Zhdanov, A.V. Ivlev, C.A. Knapek, G.E. Morfill A complex, or dusty plasma is an ionized gas containing fine particles of solid matter. These particles acquire a large negative electric charge, and due to mutual interaction and the plasma's naturally present electric fields, they arrange themselves in a regular pattern with crystalline or liquid-like order. In our experiment, polymer microspheres were suspended in the sheath of a rf discharge in argon. They settled in a 2D triangular crystalline lattice. This lattice is very soft and can be readily melted using, e.g. the radiation of a focused laser beam. The particles can be imaged directly, and their positions and velocities calculated. We performed experimental study of melting in 2D crystalline lattices using complex plasma as a model system. We found an Arrhenius dependence of the lattice defect concentration C on the kinetic temperature in steady-state experiments, and show the evidence of metastable quenching in unsteady experiments, where C follows a power-law temperature scaling. In all experiments, independent indicators suggest a grain-boundary-induced melting scenario. [Preview Abstract] |
Thursday, October 7, 2010 9:30AM - 9:45AM |
MR3.00005: Investigation of a Dusty Plasma in ECR Plasma Aleksander Drenik, Pavel Yuryev, Aref Slim, Freddy Gaboriau, Richard Clergereaux The appearance of dust in the plasma is generally considered an unwanted occurrence as the dust particles can contaminate deposited thin films, formation of dust can contribute to unwanted fuel migration in fusion reactors, etc. However, dusty plasmas can be used to create novel nanostructured materials. Formation of dust is considered to be a gas-phase process. Nonetheless, dust was observed in ECR plasmas, where due to low pressure, surface processes are strongly favored. In this experiment, the occurrence of dust in a long antennae ECR reactor was investigated. Plasma was created in pure acetylene at pressures ranging from 0.07 to 0.3 Pa. The forwarded microwave power reached up to 200 W. Dust particles were directly observed visually, indicating that the dimensions of some particles can reach well into the macroscopic scale. The curved trajectories of the particles suggest that they are confined by the magnetic field. An electrically isolated probe was used to measure the self-bias voltage of the plasma in the high magnetic field region during the experiments. The occurrence of dust was found to coincide with an increase of low frequency noise in the self-bias voltage signal and an increase of the reflected microwave power that can be related with the dust. [Preview Abstract] |
Thursday, October 7, 2010 9:45AM - 10:00AM |
MR3.00006: Negative ions and nanoparticle formation in low pressure rf plasmas Johannes Berndt, E. Kovacevic, G. Wattieaux, L. Boufendi The formation of nanoparticles in low temperature and low pressure plasmas is a complex process involving a great variety of different neutral and charged species. The understanding of the underlying mechanisms is an essential requirement for a controlled initiation or suppression of nanoparticle growth. In this contribution we focus on nanoparticle formation in a capacitively coupled discharge operated in different mixtures of noble gases with either hydrocarbons or silane as precursor gas. Despite the complexity of nanoparticle formation and its dependence on the specific chemistry, it is generally believed that negative ions play a crucial role in the early stage of this process. The role of negative ions for the nucleation of nanoparticles and their impact on the discharge characteristics (electron density, self bias etc.) is investigated both experimentally and theoretically. The investigations are performed for continuous and pulsed discharges. [Preview Abstract] |
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