Bulletin of the American Physical Society
65th Annual Gaseous Electronics Conference
Volume 57, Number 8
Monday–Friday, October 22–26, 2012; Austin, Texas
Session QR1: Plasma Modeling and Simulations II |
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Chair: Thomas Mussenbrock, Ruhr-Universit\"at Bochum Room: Amphitheatre 204 |
Thursday, October 25, 2012 10:30AM - 11:00AM |
QR1.00001: Atomic and Molecular Input Data for Plasma Modelling: a user's perspective Invited Speaker: Jan van Dijk With the advent of cheap, yet powerful computers, self-consistent numerical simulation has become a viable tool for understanding, designing and improving technological and scientific plasma sources. Nowadays, multi-dimensional models that are capable of simulating time-dependent discharge behaviour are in use at various universities and research institutes. One such computer code is Plasimo, a PLAsma SImulation MOdel that is being developed at Eindhoven University of Technology (http://plasimo.phys.tue.nl). Plasimo provides kinetic (Monte Carlo), hybrid and fluid models for transport-sensitive and equilibrium plasma. It is obvious that codes like Plasimo require a multitude of input data to function properly, but the measurement or calculation of such data is mostly outside the project's reach. In this contribution we, as Plasimo developers, will therefore provide a user's perspective of the subject of atomic and plasma data. In the first part of this contribution, we will provide an overview of the various sorts of input data that are needed for the types of plasma modelling that are supported by Plasimo. The discussion will be guided by real-world examples of models for low- and high-pressure plasma sources. In the second part of the contribution, we will discuss how modern Internet technologies can help us to fulfill our input data needs. As of today, input data are typically either hard-coded in computer programs, or read from local input files. Moreover, data pre-processing tasks, like integrating cross sections to rate coefficients, are usually carried out locally as well. We will demonstrate how Web Services (http://www.w3.org/2002/ws/) can be used to manage, disseminate and manipulate data sets more conveniently. We will also identify various input data pre-processing tasks that could be taken over by data distributors, suggest how this could be implemented, and sketch the work flow that would result from such effort. [Preview Abstract] |
Thursday, October 25, 2012 11:00AM - 11:15AM |
QR1.00002: Multi-Peaked and Stepped Electron Velocity Distributions in RF-DC Discharges with Secondary Emission A.V. Khrabrov, I.D. Kaganovich, D. Sydorenko, E.A. Startsev, L. Chen, P. Ventzek, R. Sundararajan, A. Ranjan, K. Kumar, E. Tokluoglu In RF-DC (hybrid) capacitive-coupled discharges, secondary electrons emitted from the electrodes undergo a complicated motion defined by acceleration in, and bouncing between a steady and an oscillating sheath. For the electrons that return to the RF electrode, the arrival phase is a multi-valued function of the phase in which they were emitted. This basic property leads to a velocity distribution with multiple peaks. The phase of arrival can also be discontinuous, which corresponds to a distribution containing steps. We have observed such distributions in numerical test-particle simulations, and analyzed the observed structure of the electron distributions. [Preview Abstract] |
Thursday, October 25, 2012 11:15AM - 11:30AM |
QR1.00003: Simulation of an Atmospheric Pressure Plasma Jet in a Stagnation Flow Doug Breden, Laxminarayan Raja Pulsed atmospheric pressure plasma jets (APPJs) have generated significant interest for their ability to generate non-thermal plasma in open air gaps without the risk of arcing. The plasma typically forms due to a sequence of fast ionization waves which propagate within a noble gas jet exhausting into ambient air. The resulting luminous plasma plume is safe to touch due to the non-equilibrium nature of the plasma and low gas temperatures. At the same time, high energy electrons in the ionizing head can generate reactive radical species (N and O) in addition to ions and UV radiation, which may be beneficial for biomedical applications. In order to gauge the effectiveness of these jets for treating surfaces, it is desirable to know how the plasma jet interacts with a surface and the flux of reactive species to that surface. In this work, the propagation of a single ionization wave in the stagnation flow of a helium jet impinging on a solid surface is modeled. The plasma discharge dynamics are modeled using a self-consistent, two temperature plasma solver with finite rate chemistry. The helium-jet stagnation flow is modeled using a compressible, multiple species Navier-Stokes solver. The primary objective is to determine the net delivery of reactive species to the surface and the role of parameters such as dielectric thickness. [Preview Abstract] |
Thursday, October 25, 2012 11:30AM - 11:45AM |
QR1.00004: 1D Microscale Breakdown Simulations using an Energy-Conserving, Implicit PIC-DSMC Method Chris Moore, Matthew Hopkins, Paul Crozier, Edward Barnat, Jeremiah Boerner, Russell Hooper, Matthew Bettencourt, Lawrence Musson An energy and charge conserving fully implicit formulation for electrostatic particle-in-cell (PIC) simulations with complex boundary conditions and direct simulation Monte Carlo (DSMC) particle collisions is used in this work to simulate atmospheric breakdown in small gaps. This method allows for energy conservation with arbitrarily large field-solve timesteps limited only by dynamic timescales. Momentum errors are reduced through the use of adaptive sub-stepping of the particle motion over the field-solve timestep allowing for vastly different ion and electron timesteps. Simulations of one dimensional direct current breakdown between two electrodes including electron-neutral elastic, ionization, and excitation interactions and emission of electrons from the cathode via Auger neutralization and field electron emission are presented here. The dynamics of breakdown are investigated and the breakdown voltages deviate from the Paschen curve if the Fowler-Nordheim emission flux is based on the near surface field which includes space charge effects. It is found that, early on, the primary electron generation mechanism at breakdown voltage changes from ionization/Auger neutralization in large gaps to Fowler-Nordheim emission in small gaps. [Preview Abstract] |
Thursday, October 25, 2012 11:45AM - 12:00PM |
QR1.00005: Simulation of the Partially Ionized Reacting Plasma Flow in a Negative Hydrogen Ion Source Nikolaos Gatsonis, Sergey Averkin, Lynn Olson A High Pressure Discharge Negative Ion Source (HPDNIS) operating on hydrogen is been under investigation. The Negative Ion Production (NIP) section of the HPDNIS attaches to the 10-100 Torr RF-discharge chamber with a micronozzle and ends with a grid that extracts the negative ion beam. The partially ionized and reacting plasma flow in the NIP section is simulated using an unstructured three-dimensional Direct Simulation Monte Carlo (U3DSMC) code. The NIP section contains a low-pressure plasma that includes $\mbox{H}_2 $, vibrationally-rotationally excited $\mbox{H}_2^\ast $, negative hydrogen atoms $\mbox{H}^-$, and electrons. Primary reactions in the NIP section are dissociate attachment, $\mbox{H}_2^\ast +e\to \mbox{H}^0+\mbox{H}^-$and electron collisional detachment, $e+\mbox{H}^-\to \mbox{H}+2e$. The U3DSMC computational domain includes the entrance to the NIP nozzle and the extraction grid at the exit. The flow parameters at the entrance are based on conditions in the RF-discharge chamber and are implemented in U3DSMC using a Kinetic-Moment subsonic boundary conditions method. The rotational and vibrational degrees of freedom in U3DSMC are implemented using the Larsen-Borgnakke model. Chemical reactions are implemented in U3DSMC using the Quantum-Kinetic model. Simulations cover the regime of operation of the HPDNIS and examine the flow characteristics inside the NIP section. [Preview Abstract] |
Thursday, October 25, 2012 12:00PM - 12:15PM |
QR1.00006: Inductive Plasma Discharge Modeling of a Micro Newton Radiofrequency Ionthruster ($\mu$N-RIT) Robert Henrich, Christian Heiliger Up to date challenging scientific space experiments like LISA to detect gravitational waves have high requirements especially for the thruster. One of the most promising thruster is the $\mu$N-RIT developed at the University of Giessen. This type uses an inductive plasma discharge and an extraction grid system for accelerating the ions up to a few keV. Due to this the $\mu$N-RIT fulfills the requirements of a wide range of thrust as well as the high precision of it. Also the magnitude of the power consumption is limited to about 10 W. This is slightly below of actually $\mu$N-RIT values. To meet this limitation the plasma modeling is an absolutely essential tool. The typical gas pressure in such a system is about 0.1 Pa. As a consequence validity of fluid dynamics is not guaranteed and a Particle in Cell (PIC) method could be necessary. However, PIC causes an enormous calculation consumption. Therefore, we are performing both kinds. For the fluid modeling we use the ``Comsol Multiphysics'' tool and for the PIC modeling we are developing a three dimensional massive parallelized code using MPI for all parts of the simulation. We present our first simulation results. Moreover, we compare the results of both tools and show how far the fluid simulation differs from the PIC simulation. [Preview Abstract] |
Thursday, October 25, 2012 12:15PM - 12:30PM |
QR1.00007: Modeling PECVD of photovoltaic silicon layers from hydrogen diluted silane ccrf discharges Dirk Bluhm, Stephan Danko, Oliver Schmidt, Ralf Peter Brinkmann The dynamic photovoltaic market (especially for thin film technologies) demands massive cost reduction and efficiency increase. Plasma processes play a crucial role in various solar cell technologies. Desired high quality silicon films must be deposited fast and under stable process conditions. We use a commercial fluid model (CFD-ACE+)\footnote{CFD-ACE+ User Manual, v2010.0, ESI Group, http://www.esi-cfd.com} to obtain spatiotemporal species densities and reaction rates. The chemical data set comprises of around 20 species and 80 chemical reactions. Densities obtained with a fast volume-averaged chemical model show good agreement with bulk densities from the fluid model. Care must be taken not to oversimplify chemical reaction mechanisms at pressures above 200 Pa, when polymerization processes become increasingly important. We study deposition regimes over a wide range of parameters, varying the pressure between 50 and 1000 Pa and allowing for high frequencies up to 95 MHz. Different heating mechanisms can be distinguished, leading to a different localization of radical generation. This is particularly relevant for asymmetric discharges. Process dependent radical composition and ion bombardment are analyzed, leading to design rules. Investigation of the ion bombardment by modeling the plasma sheath independently will be a subject of further research. [Preview Abstract] |
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