Bulletin of the American Physical Society
65th Annual Gaseous Electronics Conference
Volume 57, Number 8
Monday–Friday, October 22–26, 2012; Austin, Texas
Session SR1: Plasma Modeling and Simulations III |
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Chair: Ikuo Sawada, Tokyo Electron Limited Room: Amphitheatre 204 |
Thursday, October 25, 2012 3:30PM - 4:00PM |
SR1.00001: Kinetic and electromagnetic effects in technical plasmas Invited Speaker: Denis Eremin There is an accumulating body of evidence that kinetic effects play a significant role in practically all kinds of technical plasmas. Such plasmas often exhibit several groups of electrons with disparate energies, where electrons from different groups exchange energy only through weak processes. The intrinsically non-Maxwellian charachter of the electron distribution function in this case invalidates the fluid-based approaches for description of the technical plasmas. Rather, a self-consistent kinetic treatment is frequently needed for capturing all the important physics features, whereas fluid models under such conditions can yield quantitatively or even qualitatively erroneous results. Despite this, the fluid-based numerical codes remain a popular tool for investigation of the technical plasmas due to the low computational cost of such codes compared to that of the kinetic ones. The proper description of technical plasmas becomes further complicated if in addition to the kinetic treatment one needs to consider electromagnetic effects, which gain in significance as the electrode size and driving frequency increase, which continues to be the tendency in many CCP industrial plasmas usually described under the electrostatic approximation. In this talk we discuss modern techniques of parallelization of self-consistent kinetic particle-in-cell/Monte-Carlo (PIC/MCC) numerical codes on graphics cards (GPUs), which make kinetic simulations a routine numerical tool for investigation of technical plasmas. Then, we will demonstrate for the plasmas spanning broad parameter range examples of simulations made with such codes, where kinetic effects are important and thus the fluid description is inadequate. Finally, we argue that in many situations the electromagnetic effects relevant to the technical plasmas can be described in the framework of Darwin (magneto-inductive) approximation, which can be implemented as a natural modification in an electrostatic PIC/MCC code, as all the field equations are elliptic. We give the examples of kinetic simulations with electromagnetic effects obtained with such Darwin code. [Preview Abstract] |
Thursday, October 25, 2012 4:00PM - 4:15PM |
SR1.00002: Thermal mechanism of prepeak formation in Pulsed Glow Discharge Maxim Voronov, Volker Hoffmann, Tobias Steingrobe, Wolfgang Buscher, Carsten Engelhard, Andrew Storey, Steven Ray, Gary Hieftje A microsecond Pulsed Glow Discharge ($\mu $s PGD) in a Grimm-type source is characterized by the so-called ``prepeak,'' which is a spike in both electrical current and emission intensity at the leading edge of the discharge pulse. The prepeak is followed by synchronized vibrations of the current and the emission. To understand the nature of these phenomena, a microphone was inserted into the discharge chamber. Acoustical waves were detected and found to be in correlation with the measured vibrations. This points to a thermal mechanism for prepeak formation: the gas is heated in the leading edge of the discharge pulse and then expanded. To prove this suggestion, a Monte-Carlo based model was developed to simulate the evolution of Ar concentration, temperature, and flow in time and space. Potentially, the model could be used for gas simulations in a wide range of different applications. Here, the model is incorporated into an existing but modified model of the $\mu $s PGD in a Grimm-type plasma excitation source. Results of the simulations confirm that the thermal mechanism is responsible for the formation of the electrical prepeak and the pressure waves. [Preview Abstract] |
Thursday, October 25, 2012 4:15PM - 4:30PM |
SR1.00003: 3D Hydrodynamic Simulations of Atmospherc-Pressure Inductively-Coupled Plasma Torches and Microwave Plasma Torches Peter Williams We have performed fully 3D hydrodynamic simulations of atmospheric-pressure inductively coupled plasma (ICP) torches and microwave plasma (MP) torches. These simulations closely mirror the plasma conditions in ICP and MP torches designed for elemental analysis in commercial ICP-MS and MP-OES systems. Towards the goal of understanding transport in our torches, we show when and where we believe these torches may have turbulent flow. Our goal is to understand and hopefully reduce such turbulence as it is thought to lead to reduced instrumental sensitivity. Previous literature that investigated turbulence in ICPs via simulation has largely done so using 2D hydrodynamic simulations coupled with turbulence models such as k-epsilon. The advantage of this approach is an enormous savings in computational cost. The disadvantage is that models are only rough approximate representations of reality, and may give misleading results in some cases. Swirling flows in particular, such as exist in virtually all commercial ICP torches, present notoriously difficult problems for most turbulence models. It is for this reason that we have attempted to capture the turbulent breakdown directly. This requires high-resolution 3D simulations, which we have performed using the commercial package CFD-ACE. [Preview Abstract] |
Thursday, October 25, 2012 4:30PM - 4:45PM |
SR1.00004: Simulations of pulsed rf plasma sources using CFD-ACE+ Mustafa Megahed, Ananth Bhoj, Sing Ki Nam, Raj Dhindsa Pulsing techniques are increasingly being used in plasma processing reactors for newer technological nodes. Pulsed rf sources allow for additional ``knobs'' to control plasma parameters. In particular, varying the pulsing frequency, duty cycle and pulse shape enables manipulation of the fluxes and energy distribution functions. Accurate numerical simulations of pulsed discharges require that transients are tracked. Time scales for the rf signals, pulsing frequency and the neutral / heavy species response times can span orders of magnitude posing a significant challenge. The multi-physics modeling platform CFD-ACE+ was used in this work to address simulations of an Ar discharge in a typical CCP reactor configuration. The effect of pulsing on plasma characteristics was investigated. Initial results comparing the continuous and pulsed rf operating modes will be discussed. [Preview Abstract] |
Thursday, October 25, 2012 4:45PM - 5:00PM |
SR1.00005: Links between vortex formation and ambipolar flow in 2D ICP fluid simulations David Urrabazo, Matthew Goeckner Recent results by Bogdanov, et al., have suggested the presence of vortices within discharges. They have reported that these are related to a gradient in the electron temperature. We have also examined these vortices via fluid simulation of an ICP discharge developed with COMSOL 3.5a and Matlab. We will show via an examination of the curl of the electron flux that the source of the vortices is more complex then what was reported by Bogdanov, et al. Specifically, we will show that the source of is via several channels - often tied to the electron temperature profile but not necessarily directly related to the profile. Further, as the components related to these vortices are removed, the classic fluid model is reduced to the ambipolar model. This suggests that there are other ways to envision the ambipolar model outside of the requirement for flux congruence. [Preview Abstract] |
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