Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session PO7: Low-temperature Plasma Science, Engineering and Technology |
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Chair: Igor Kaganovich, Princeton Plasma Physics Laboratory Room: 212 AB |
Wednesday, November 2, 2016 2:00PM - 2:12PM |
PO7.00001: Thin film deposition using rarefied gas jet Dr. Sahadev Pradhan The rarefied gas jet of aluminium is studied at Mach number \textit{Ma }$=$\textit{ (U\textunderscore j / }$\backslash $\textit{sqrt\textbraceleft kb T\textunderscore j / m\textbraceright )}in the range \textit{.01 \textless Ma \textless 2}, and Knudsen number \textit{Kn }$=$\textit{ (1 / (}$\backslash $\textit{sqrt\textbraceleft 2\textbraceright }$\backslash $\textit{pi d\textasciicircum 2 n\textunderscore d H)} in the range \textit{.01 \textless Kn \textless 15}, using two-dimensional (2D) direct simulation Monte Carlo (DSMC) simulations, to understand the flow phenomena and deposition mechanisms in a physical vapor deposition (PVD) process for the development of the highly oriented pure metallic aluminum thin film with uniform thickness and strong adhesion on the surface of the substrate in the form of ionic plasma, so that the substrate can be protected from corrosion and oxidation and thereby enhance the lifetime and safety, and to introduce the desired surface properties for a given application. Here, $H$is the characteristic dimension, \textit{U\textunderscore j}and \textit{T\textunderscore j}are the jet velocity and temperature, \textit{n\textunderscore d}is the number density of the jet, $m$and $d$ are the molecular mass and diameter, and \textit{kb}is the Boltzmann constant. An important finding is that the capture width (cross-section of the gas jet deposited on the substrate) is symmetric around the centerline of the substrate, and decreases with increased Mach number due to an increase in the momentum of the gas molecules. DSMC simulation results reveals that at low Knudsen number \textit{((Kn }$=$\textit{ 0.01);}shorter mean free paths), the atoms experience more collisions, which direct them toward the substrate. However, the atoms also move with lower momentum at low Mach number$,$which allows scattering collisions to rapidly direct the atoms to the substrate. [Preview Abstract] |
Wednesday, November 2, 2016 2:12PM - 2:24PM |
PO7.00002: A comparison of continuum and kinetic simulations of microplasmas integrated with high secondary yield cathodes Arghavan Alamatsaz, Abhishek Kumar Verma, Ayyaswamy Venkattraman During the last two decades, microplasmas have become an active area of research in the field of low-temperature plasma science and engineering with a wide range of applications including electronics, nanomaterial synthesis and metamaterials to name a few. Kinetic and continuum methods are commonly employed numerical simulation techniques to study the low temperature plasmas. The uncertainty and imprecision associated with input parameters used in these models impose a constraint on fidelity of the simulation results. In this work, these computational techniques are compared in the context of modeling microplasmas driven by cathodes with high secondary electron emission coefficient. Simulations of argon microplasmas operating at a moderate pd (pressure*distance between electrodes) are performed using particle-in-cell with Monte Carlo collisions (PIC-MCC), and fluid model using the full momentum equations for both electrons and ions. Results obtained for plasma density, potential, electric field and electron temperature using continuum simulations are compared with the corresponding PIC-MCC simulations as benchmark. These numerical experiments provide insights on importance of input parameters in fluid model for high fidelity simulation of microplasma applications. [Preview Abstract] |
Wednesday, November 2, 2016 2:24PM - 2:36PM |
PO7.00003: Computer Simulation of Synthesis of Boron-Nitride Nanostructures Predrag Krstic, Longtao Han Synthesis of boron-nitride fullerenes, nano-cocoons and nano-cages by self-organization of BN molecules in a high-temperature plasma is simulated with the DFT tight-binding method. No boron nano-cluster or catalytic nanoparticles are needed to initiate this process. By varying the plasma temperature, incoming flux of BN molecule, and the total time of growth, we can simulate growth of sp$^{\mathrm{2}}$ cages of various shape, size and quality. Role of hydrogen in the syntheses is also considered, with the simulation of HBNH and H$_{\mathrm{2}}$BNH$_{\mathrm{2}}$ molecules as feedstock. [Preview Abstract] |
Wednesday, November 2, 2016 2:36PM - 2:48PM |
PO7.00004: Characterizing configurable transmission modes in plasma photonic crystals using scanning field mapping Benjamin Wang, Mark Cappelli A~ fully~ tunable~ plasma~ photonic~ crystal~ is~ used~ to~ control~ the propagation~ of~ free~ space~ electromagnetic~ waves~ in~ the~ S~ to X~ band~ of~ the~ microwave~ spectrum.~ A~ structured~ array~ of discharge~ plasma~ tubes~ are~ arranged~ in~ a~ square~ crystal~ lattice with~ the~ individual~ plasma~ dielectric~ constant~ tuned~ through variation~ in~ the~ plasma~ density.~ Microwave field-mapping is used to characterize the transmitted electromagnetic fields of the tunable~device~operating in waveguiding~and~bending~modes. These modes are obtained by introducing appropriate line defects in the photonic crystal structure by controlling the activity of individual plasma tubes. Comparisons are made of the measured fields to those simulated using commercially-available software. [Preview Abstract] |
Wednesday, November 2, 2016 2:48PM - 3:00PM |
PO7.00005: Ion Concentration vs. Depth Modelling Code for Plasma Ion Implantation Michael Bradley, Marcel Risch Plasma Ion Implantation (PII) is a technique in which a solid target immersed in a plasma is implanted with energetic ions via the application of a pulsed kilovolt-level negative bias voltage. PII allows implantation of very high ion fluences across broad-area targets. This makes it an ideal technique for many applications, including semiconductor device fabrication. When using PII, it is important to accurately model the resulting ion concentration vs. depth profile. We start with a model due to M.A. Lieberman for dynamic sheath expansion, in which the equation for the time-dependent sheath thickness $s(t)$ is solved numerically for an arbitrary pulse voltage profile $V(t)$ and used to obtain the implanted ion current density $J(t)$. This model must be extended to account for a number of additional effects including collisions in the high-voltage sheath, plasma density enhancement during the high voltage pulse due to the effect of secondary electrons, and plasma depletion in the sheath. This talk will describe the ion concentration vs. depth prediction code which was developed by our group based on this approach. [Preview Abstract] |
Wednesday, November 2, 2016 3:00PM - 3:12PM |
PO7.00006: The layered structure of the carbon arc discharge plasma. Vladislav Vekselman, Brentley Stratton, Yevgeny Raitses The arc discharge with a consumed anode is commonly used for synthesis of nanomaterials such as fullerenes, nanotubes [1] and, more recently, graphene [2]. The role of the arc plasma in nanosynthesis processes, including ablation of the graphite anode, nucleation and growth of nanostructures remains unclear. Our recent fast frame camera measurements revealed arc oscillations associated with the ablation processes at the anode. More sophisticated measurements using optical emission spectroscopy and spectrally resolved fast framing imaging revealed the complex, layered structure of plasma species distribution, which is dynamically changing. The results of this research include time- and space- resolved distributions of plasma species, plasma electron density and temperature. The obtained experimental data suggest a strong correlation between arc plasma parameters and nanosynthesis processes. [1] S. Iijima, Helical Microtubules of Graphitic Carbon, Nature 354, 56 (1991). [2] A. Shashurin and M. Keidar, Synthesis of 2D materials in arc plasmas, J Phys D Appl Phys 48 (2015). [Preview Abstract] |
Wednesday, November 2, 2016 3:12PM - 3:24PM |
PO7.00007: Experimental Investigation of Molecular Species Formation in Metal Plasmas During Laser Ablation H. Radousky, J. Crowhurst, T. Rose, M. Armstrong, E. Stavrou, J. Zaug, D. Weisz, M. Azer, M. Finko, D. Curreli Atomic and molecular spectra on metal plasmas generated by laser ablation have been measured using single, nominally 6-7 ns pulses at 1064 nm, and with energies less than 50 mJ. The primary goal for these studies is to constrain the physical and chemical mechanisms that control the distribution of radionuclides in fallout after a nuclear detonation. In this work, laser emission spectroscopy was used to obtain \textit{in situ }data for vapor phase molecular species as they form in a controlled oxygen atmosphere for a variety of metals such as Fe, Al, as well as preliminary results for U. In particular, the ablation plumes created from these metals have been imaged with a resolution of $\sim$ 10 ns, and it is possible to observe the expansion of the plume out to 0.5 us. These data serve as one set of inputs for a semi-empirical model to describe the chemical fractionation of uranium during fallout formation. [Preview Abstract] |
Wednesday, November 2, 2016 3:24PM - 3:36PM |
PO7.00008: Global Modeling of Uranium Molecular Species Formation Using Laser-Ablated Plasmas Davide Curreli, Mikhail Finko, Magdi Azer, Mike Armstrong, Jonathan Crowhurst, Harry Radousky, Timothy Rose, Elissaios Stavrou, David Weisz, Joseph Zaug Uranium is chemically fractionated from other refractory elements in post-detonation nuclear debris but the mechanism is poorly understood. Fractionation alters the chemistry of the nuclear debris so that it no longer reflects the chemistry of the source weapon. The conditions of a condensing fireball can be simulated by a low-temperature plasma formed by vaporizing a uranium sample via laser heating. We have developed a global plasma kinetic model in order to model the chemical evolution of U/UOx species within an ablated plasma plume. The model allows to track the time evolution of the density and energy of an uranium plasma plume moving through an oxygen atmosphere of given fugacity, as well as other relevant quantities such as average electron and gas temperature. Comparison of model predictions with absorption spectroscopy of uranium-ablated plasmas provide preliminary insights on the key chemical species and evolution pathways involved during the fractionation process. [Preview Abstract] |
Wednesday, November 2, 2016 3:36PM - 3:48PM |
PO7.00009: Instability of a Short Anodic Arc Used for Synthesis of Nanomaterials Sophia Gershman, Yevgeny Raitses The short anodic arc discharge is used for the synthesis of nanomaterials and had been presumed stable. We report the results of electrical and fast imaging measurements that reveal a combined motion of the arc column and the arc attachment region to the anode when the arc is operated with a high ablation rate. The arc exhibits a negative differential resistance before the arc motion occurs. The observed arc motion correlates with the arc voltage and current oscillations. The characteristic time of these instabilities is in a 10$^{-3}$ sec range. Thermal processes in the arc plasma region interacting with the ablating anode are considered as possible causes of this unstable arc behavior. The measured negative differential resistance of the arc during the oscillations indirectly supports the thermal model. Our model suggests that the injection of the ablating material into the plasma locally reduces the energy flux to the surface and leads to the arc shifting to the adjacent position. The observed arc motion can potentially cause the mixing of the various nanoparticles synthesized in the arc in the high ablation regime leading to the poor selectivity characteristic of the arc synthesis of nanomaterials. [Preview Abstract] |
Wednesday, November 2, 2016 3:48PM - 4:00PM |
PO7.00010: Migration of Carbon Adatoms on the Surface of Charged SWCNT Longtao Han, Predrag Krstic, Igor Kaganovich In volume plasma, the growth of SWCNT from a transition metal catalyst could be enhanced by incoming carbon flux on SWCNT surface, which is generated by the adsorption and migration of carbon adatoms on SWCNT surface. In addition, the nanotube can be charged by the irradiation of plasma particles. How this charging effect will influence the adsorption and migration behavior of carbon atom has not been revealed. Using Density Functional Theory, Nudged Elastic Band and Kinetic Monte Carlo method, we found equilibrium sites, vibrational frequency, adsorption energy, most probable pathways for migration of adatoms, and the barrier sizes along these pathways. The metallic (5,5) SWCNT can support a fast migration of the carbon adatom along a straight path with low barriers, which is further enhanced by the presence of negative charge on SWCNT. The enhancement is contributed by the higher adsorption energy and thence longer lifetime of adatom on the charged SWCNT surface. The lifetime and migration distance of adatom increase by three and two orders of magnitude, respectively, as shown by Kinetic Monte Carlo simulation. These results support the surface migration mechanism of SWCNT growth in plasma environment. [Preview Abstract] |
Wednesday, November 2, 2016 4:00PM - 4:12PM |
PO7.00011: A Computational Framework for Efficient Low Temperature Plasma Simulations Abhishek Kumar Verma, Ayyaswamy Venkattraman Over the past years, scientific computing has emerged as an essential tool for the investigation and prediction of low temperature plasmas (LTP) applications which includes electronics, nanomaterial synthesis, metamaterials etc. To further explore the LTP behavior with greater fidelity, we present a computational toolbox developed to perform LTP simulations. This framework will allow us to enhance our understanding of multiscale plasma phenomenon using high performance computing tools mainly based on OpenFOAM FVM distribution. Although aimed at microplasma simulations, the modular framework is able to perform multiscale, multiphysics simulations of physical systems comprises of LTP. Some salient introductory features are capability to perform parallel, 3D simulations of LTP applications on unstructured meshes. Performance of the solver is tested based on numerical results assessing accuracy and efficiency of benchmarks for problems in microdischarge devices. Numerical simulation of microplasma reactor at atmospheric pressure with hemispherical dielectric coated electrodes will be discussed and hence, provide an overview of applicability and future scope of this framework. [Preview Abstract] |
Wednesday, November 2, 2016 4:12PM - 4:24PM |
PO7.00012: Detailed Kinetic Modeling of Processes Relevant To Fusion Energy Marco Mehl, Michael Armstrong, Joseph Zaug, Jonathan Crowhurst, Harry Radousky, Elissaios Stavrou Carbon based materials have been proposed as candidates for the fabrication of plasma--facing components in the design of fusion energy devices. Although these components are not supposed to be in direct contact with the core fusion plasma, plasma instabilities and the harsh environment they are exposed to can cause the degradation of plasma-exposed components and the transfer of contaminants into the plasma followed by deposition of byproducts. In order to investigate the chemistry involved in these processes and to assist the development of models suitable to understand the long term consequences of the carbon ablation/deposition cycle, an inductively coupled plasma flow reactor (ICPFR) has been developed. The ICPFR allows the atomization of carbon containing precursors to high temperatures (in the order of 10000K) and the characterization of the gas and solid species formed downsteam from the plasma source through spectroscopic techniques. In parallel to the experimental analysis a comprehensive set of fluid dynamic and detailed kinetic simulations are used to analyze the data. The combination of these two approaches resulted in a validated and comprehensive chemical model for the formation of carbon deposits in carbon contaminated cooling plasmas. [Preview Abstract] |
Wednesday, November 2, 2016 4:24PM - 4:36PM |
PO7.00013: Why Nuclear Forensics Needs New Plasma Chemistry Data T. Rose, M. Armstrong, A. Chernov, J. Crowhurst, Z. Dai, K. Knight, B. Koroglu, H. Radousky, E. Stavrou, D. Weisz, J. Zaug, M. Azer, M. Finko, D. Curreli The mechanisms that control the distribution of radionuclides in fallout after a nuclear detonation are not adequately constrained. Current capabilities for assessing post-detonation scenarios often rely on empirical observations and approximations. Deeper insight into chemical condensation requires a coupled experimental, theoretical, and modeling approach. The behavior of uranium during plasma condensation is perplexing. Two independent methods are being developed to investigate gas phase uranium chemistry and speciation during plasma condensation: (1) laser-induced breakdown spectroscopy and (2) a unique steady-state ICP flow reactor. Both methods use laser absorption spectroscopy to obtain \textit{in situ} data for vapor phase molecular species as they form. We are developing a kinetic model to describe the relative abundance of uranium species in the evolving plasma. Characterization of the uranium-oxygen system will be followed by other chemical components, including `carrier' materials such as silica. The goal is to develop a semi-empirical model to describe the chemical fractionation of uranium during fallout formation. [Preview Abstract] |
Wednesday, November 2, 2016 4:36PM - 4:48PM |
PO7.00014: Preliminary Experimental Results using a Steady State ICP Flow Reactor to Investigate Condensation Chemistry for Nuclear Forensics Batikan Koroglu, Mike Armstrong, Mark Cappelli, Alex Chernov, Jonathan Crowhurst, Marco Mehl, Harry Radousky, Timothy Rose, Joe Zaug The high temperature chemistry of rapidly condensing matter is under investigation using a steady state inductively coupled plasma (ICP) flow reactor. The objective is to study chemical processes on cooling time scales similar to that of a low yield nuclear fireball. The reactor has a nested set of gas flow rings that provide flexibility in the control of hydrodynamic conditions and mixing of chemical components. Initial tests were run using two different aqueous solutions (ferric nitrate and uranyl nitrate). Chemical reactants passing through the plasma torch undergo non-linear cooling from \textasciitilde 10,000K to 1,000K on time scales of \textless 0.1 to 0.5s depending on flow conditions. Optical spectroscopy measurements were taken at different positions along the flow axis to observe the in situ spatial and temporal evolution of chemical species at different temperatures. The current data offer insights into the changes in oxide chemistry as a function of oxygen fugacity. The time resolved measurements will also serve as a validation target for the development of kinetic models that will be used to describe chemical fractionation during nuclear fireball condensation. [Preview Abstract] |
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