Bulletin of the American Physical Society
67th Annual Gaseous Electronics Conference
Volume 59, Number 16
Sunday–Friday, November 2–7, 2014; Raleigh, North Carolina
Session DT2: Plasma Modeling and Simulations I |
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Chair: Miles Turner, National Center for Plasma Science Technology, Dublin City University Room: State C |
Tuesday, November 4, 2014 10:00AM - 10:15AM |
DT2.00001: Numerical Simulations for ICP Source for Implant Applications Vladimir Kudriavtsev, Babak Adibi, Terry Bluck, Vladimir Kolobov ICP Plasma source characteristics depend significantly on cavity aspect ratio and operating pressure [1]. In this work we investigate the effect of chamber height and antenna coil placement on current flux and plasma uniformity at pressures in 5mtorr -- 1torr range and also study computationally appropriate scaling laws. Cavity dimensions are 0.2x0.2 m. CFD-ACE/Plasma software is used to conduct 2D planar plasma simulations for Ar and H2 plasmas. Software allows use of unstructured and non-uniform mesh to resolve geometry details. At low pressure plasma peaks in the middle of the cavity even when RF antenna is placed on top. Results show that there is a maximum in plasma density that corresponds with a unique aspect ratio. \\[4pt] [1] C. Biloiu, et al., US Patent 8,590,485B2 [Preview Abstract] |
Tuesday, November 4, 2014 10:15AM - 10:30AM |
DT2.00002: Hybrid Global Model Simulations of He/N$_2$ and He/H$_2$O Atmospheric Pressure Capacitive Discharges M.A. Lieberman, E. Kawamura, Ding Ke, A.J. Lichtenberg, P. Chabert, C. Lazzaroni We used 1D particle-in-cell (PIC) simulations of an atmospheric He/0.1\%N$_2$ discharge with simplified chemistry to guide the development of a hybrid analytical/numerical global model that includes electron multiplication and two classes of electrons: ``hot'' electrons associated with the sheaths, and ``warm'' electrons associated with the bulk. The model and PIC results show reasonable agreement and indicate a transition from a low power $\alpha$-mode with a relatively high bulk electron temperature T$_e$ to a high power $\gamma$-mode with a low T$_e$. The transition is accompanied by an increase in density and a decrease in sheath widths. Water is a trace gas of bio-medical interest since it may arise from contact with skin. We use the hybrid global model to simulate a chemically complex, bounded He/H$_2$O atmospheric pressure discharge, including 148 volume reactions among 43 species, and including clusters up to H$_{19}$O$_9^+$. For a planar discharge with a 1 cm electrode radius and a 0.5 mm gap driven at 13.56 MHz, we determine the depletion and diffusion effects and the $\alpha$ to $\gamma$ transition for secondary emission $\gamma_{se}$=0.25 over a range of rf currents and external H$_2$O concentrations. Each simulation takes about 2 minutes on a moderate laptop. [Preview Abstract] |
Tuesday, November 4, 2014 10:30AM - 10:45AM |
DT2.00003: The effect of including fast neutrals and energy-dependent $\gamma $-coefficients in PIC simulations of capacitive RF plasmas Julian Schulze, Aranka Derzsi, Ihor Korolov, Zoltan Donko, Edmund Schuengel In most PIC simulations of capacitive RF plasmas operated in noble gases only electrons and ions are traced and a constant ion induced secondary electron emission coefficient of $\gamma_{\mathrm{ion}}\approx $ 0.1 is used. Here, we demonstrate that tracing fast neutrals that originate from elastic ion-atom collisions in the sheaths, including ionization as well as secondary electron emission induced by these particles, and implementing realistic energy dependent $\gamma $-coefficients are essential for obtaining realistic results from such simulations. We find that the ionization caused by fast neutrals strongly enhances the plasma density in simulations of argon discharges driven at 13.56 MHz. This leads to smaller sheaths and limits the maximum driving voltage amplitudes, at which the simulation converges. Both effects are in agreement with experimental findings. Including realistic $\gamma $-coefficients also affects the plasma density and other process relevant parameters such as the ion energy and flux at the electrodes. The correct implementation of the energy dependence of secondary electron emission is found to have a drastic effect, if global control parameters used to change the ion bombardment energy in applications are tuned. [Preview Abstract] |
Tuesday, November 4, 2014 10:45AM - 11:00AM |
DT2.00004: Modeling Argon Plasma Excimer Characteristics near a Dielectric Surface in Miniaturized Volumes Ashraf Farahat, Emad Ramadan We computationally model plasma -neutral gas dynamics in a miniaturized microthruster encloses Ar and contains a dielectric material sandwiched between two metal plates using a two dimensional plasma model. Spatial and temporal plasma properties are investigated by solving the Poisson equation with the conservation equations of charged and excited neutral plasma species. We find the microthruster properties to depend on small changes in the secondary electron emission coefficient that could result from dielectric erosion and aging. The changes also affect the electrohydrodynamic force produced when we use the microthruster to generate thrust for small spacecrafts. The electrohydrodynamic force is calculated and found to be significant in the sheath area near the dielectric layer and is found to affect gas flow dynamics including the Ar excimer formation and density. The plasma-neutral gas momentum exchange is significant in affecting gas flow dynamics and in the formation of excimer species in addition to affecting the UV and visible emission characteristics of the device. [Preview Abstract] |
Tuesday, November 4, 2014 11:00AM - 11:15AM |
DT2.00005: Study of whole channel discharge characteristics of Hall Thruster under different voltages Duan Ping We used the method of Particle-in-Cell to stimulate the distribution of electron density, ion density and electron temperature with different discharge voltages in a Hall thruster channel. The variation of specific impulse with the discharge voltage was also discussed. It was found that maximum electron and ion densities are gained at the axial 15mm when the discharge voltage is ranging from 250V to 650V and the electron temperature peak emerges near the channel outlet of small axial distance. Under the condition of 700V or higher discharge voltages, highest electron temperature expands in the axial direction and the maximum densities are located in the anode vicinity where the ionization region is limited to. It also revealed that specific impulse increases with the increase of discharge voltage. [Preview Abstract] |
Tuesday, November 4, 2014 11:15AM - 11:30AM |
DT2.00006: A Hybrid PIC/DSMC Model of Breakdown in Triggered Vacuum Spark Gaps Stan G. Moore, Christopher H. Moore, Jeremiah J. Boerner Triggered vacuum spark gaps (TVSGs) can be used as high voltage, high current switches with a fast switching time and a variable operating voltage, such as in pulsed power applications and crowbar circuits that protect against overvoltage conditions. Hybrid particle-in-cell (PIC) [1] and direct simulation Monte Carlo (DSMC) [2] methods can be used to simulate breakdown in TVSGs. In this talk, we present results of a one-dimensional hybrid PIC/DSMC model and show that changing the density and velocity of injected neutral particles (which can be related to the surface temperature) significantly changes both the time to breakdown and the existence of a short-lived starvation mode in the current waveform.\\[4pt] Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. \\[4pt] [1] C. K. Birdsall and A. B. Langdon, \textit{Plasma Physics via Computer Simulation}, McGraw-Hill, New York (2005).\\[0pt] [2] G. A. Bird, \textit{Molecular Gas Dynamics and the Direct Simulation of Gas Flows}, Oxford University Press, Oxford, UK (1994). [Preview Abstract] |
Tuesday, November 4, 2014 11:30AM - 11:45AM |
DT2.00007: Testing fluid models of different order on streamer discharges Aram Markosyan, Jannis Teunissen, Sasha Dujko, Ute Ebert We have compared several fluid models for streamer discharges, namely the recently developed high order fluid model [Dujko et al, J. Phys. D, 46:5202, 2013], the classical first order model using the local field approximation and the second order fluid model using the local energy approximation with drift-diffusion approximation. Simulation results for planar negative ionization fronts with all three fluid models are presented and compared. As a reference, we use a particle-in-cell/Monte Carlo (PIC/MC) model. All tests are performed for neon and nitrogen at STP for a wide range of reduced electric fields. Our simulation results show large deviations between the models for various properties of negative planar fronts. We discuss the practical and theoretical aspects of applicability of each fluid model. [Preview Abstract] |
Tuesday, November 4, 2014 11:45AM - 12:00PM |
DT2.00008: Investigating the guiding of streamers in nitrogen/oxygen mixtures with 3D simulations Jannis Teunissen, Sander Nijdam, Eiichi Takahashi, Ute Ebert Recent experiments by S. Nijdam and E. Takahashi have demonstrated that streamers can be guided by weak pre-ionization in nitrogen/oxygen mixtures, as long as there is not too much oxygen (less than 1\%). The pre-ionization was created by a laser beam, and was orders of magnitude lower than the density in a streamer channel. Here, we will study the guiding of streamers with 3D numerical simulations. First, we present simulations that can be compared with the experiments and confirm that the laser pre-ionization does not introduce space charge effects by itself. Then we investigate topics as: the conditions under which guiding can occur; how photoionization reduces the guiding at higher oxygen concentrations and whether guided streamers keep their propagation direction outside the pre-ionization. [Preview Abstract] |
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