Bulletin of the American Physical Society
73rd Annual Gaseous Electronics Virtual Conference
Volume 65, Number 10
Monday–Friday, October 5–9, 2020; Time Zone: Central Daylight Time, USA.
Session KT2: Modeling and Simulation: Validation and Verification ILive
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Chair: Miles Turner, Dublin City University |
Tuesday, October 6, 2020 3:00PM - 3:15PM Live |
KT2.00001: Electrostatic wave propagation in the presence of secondary electrons in low pressure capacitively coupled plasmas Katharina Noesges, Julian Schulze, Mate Vass, Zoltan Donko, Peter Hartmann, Thomas Mussenbrock, Ralf Peter Brinkmann, Sebastian Wilczek In capacitively coupled radio frequency (CCRF) discharges, the expanding plasma sheath generates electrostatic waves which propagate through the plasma bulk. This wave propagation is frequently evidenced in Particle-In-Cell / Monte Carlos collisions (PIC/MCC) simulations in the low pressure regime ($p \approx 1$ Pa) by the spatio-temporal distribution of the displacement current density. By considering ion induced secondary electron emission, electrons are generated at the plasma boundary surface and are accelerated by the RF-oscillating sheath electric field. This leads to a stronger excitation of the waves, in which the amplitude of the displacement current density increases by raising the secondary electron (SE) emission yield. In addition, the dynamics of the SEs are also coupled with the wave propagation. By including SEs, a particular spatio-temporal ionization structure develops in which the velocity corresponds to that of the electrostatic wave and intensifies the ionization process. In this low pressure regime the beam of SEs can bounce multiple times through the discharge and lead to nonlocal effects, especially at the boundary sheaths. In order to study this phenomenon, 1d3v PIC/MCC simulations of a symmetric CCRF discharge are performed. [Preview Abstract] |
Tuesday, October 6, 2020 3:15PM - 3:30PM Live |
KT2.00002: Validation of the Smooth Step Model Ralf Peter Brinkmann, Maximilian Klich, Thomas Mussenbrock, Sebastian Wilczek The Smooth Step Model (SSM) establishes an approximate closed-form expression for the spatially and phase-resolved electric field in an RF-modulated plasma boundary sheath. The model takes thermal (finite electron temperature) and dynamic (finite electron mass) effects into account in leading order perturbation theory. It provides (i) the space charge field in the electron-depleted sheath, (ii) the generalized Ohmic and ambipolar field in the quasineutral plasma, and (iii) a smooth interpolation for the transition in between. This contribution compares the Smooth Step Model with a outcome of a self-consistent Particle-in-Cell/Monte Carlo Collisions simulation of a capacitive RF plasma (argon at 3 Pa/13.56 MHz). It is found that the maximal relative deviation of the local field is (as expected) in the percentage range. The error for the integrated field, i.e., the sheath voltage, is below one percent. [Preview Abstract] |
Tuesday, October 6, 2020 3:30PM - 3:45PM Live |
KT2.00003: The role of initial noise in PIC and Vlasov simulations of the Buneman instability A. Tavassoli, O. Chapurin, M. Jimenez Jimenez, T. Zintel, M. Papahn Zadeh, M. Shoucri, R. Spiteri, L. Coudel, A. Smolyakov In this work, we analyze effect of the noise in the PIC simulations on the development of the Buneman type instability driven by the relative drift velocity $v_{0}$ of the electrons, with respect to the ions in an unmagnetized plasma. We consider a regime of relatively low values of the drift velocity $v_{0}=2v_{te}$. A series of highly resolved PIC simulations with increasingly large number of particles per cell is performed using several different in-house, publicly available, and commercial PC codes. All codes predict very similar growth rates, but several times different from the linear growth rate calculated from the linear theory. We then repeat the simulations for the same system with grid based Vlasov solvers, with low noise level. The results from Vlasov solvers are quite consistent with the exact growth rates from the linear dispersion relation. It has been conjectured that the inherent noise in the initial condition of PIC simulations result in early trapping of the electrons thus affecting the linear growth even at very initial stages. To confirm this effect, the simulations with the Vlasov solvers were repeated but starting with the same initial conditions and the same level of the initial noise as in PIC simulations. In this case, we see the growth of the modes similar to the PIC simulations and inconsistent with the linear theory. [Preview Abstract] |
Tuesday, October 6, 2020 3:45PM - 4:00PM Live |
KT2.00004: 2D radial-azimuthal Particle-In-Cell benchmark for ExB discharges Willca Villafana, Anne Bourdon, Pascal Chabert, Benedicte Cuenot, Ken Hara, Marilyn Jimenez, Federico Petronio, Andrei Smolyakov, Francesco Taccogna, Antoine Tavant, Olivier Vermorel Plasma applications require a deep understanding of the complex interactions of particles with walls. In the example of ExB devices, such interactions can be greatly altered by the magnetic field. While ions are immune to it, electrons are strongly magnetized, which can trigger the development of a variety of coupled instabilities. The latter can dramatically increase electronic temperatures, that could be an issue near the walls. Such intricate physics may be studied with simulation, in particular with Particle-In-Cell (PIC) methods which are robust and accurate. Unfortunately, there is no theoretical reference to validate the results. To give confidence in the numerical solution, code comparison is proposed. Thus, in this work five groups using independent PIC codes joined their efforts to carefully set up step by step a 2D radial-azimuthal simulation. Along this incremental process, mean parameters and characteristic instabilities have been systematically compared and were found similar. Results may be then used by the community for code benchmarking. This work is part of the Landmark project and complements previous 2D axial-azimuthal studies. [Preview Abstract] |
Tuesday, October 6, 2020 4:00PM - 4:15PM Live |
KT2.00005: Particle-in-cell simulation of multi-frequency low-pressure capacitively-coupled plasma Jun-Chieh Wang, Peng Tian, Jason Kenney, Shahid Rauf, Ihor Korolov, Julian Schulze Multi-frequency capacitively coupled plasmas (CCPs) at low pressure (\textless 10's mTorr) are essential for critical plasma processing applications such as high aspect ratio (HAR) dielectric etching for 3D memory fabrication. To meet the stringent requirement of optimum feature profile and high etch rate, plasma simulation has been used to help design the industrial CCPs in the hope of accurately controlling the ion energy and ratio of ion to radical flux. Significant effort and progress have been made to improve plasma models over the past few decades. Having said that, high-quality measurements of ion energy distribution functions (IEDF) in low-pressure CCPs are still in high demand for model validation. In this paper, a 1D particle-in-cell (PIC) simulation is used to study the kinetic behavior of charge species in low pressure (a few to 10's mTorr) multi-frequency (100s kHz to 10s MHz) Ar CCPs. Measurements from the corresponding experiments are compared to our 1D PIC model. With pressure as low as 2 mTorr, a double-peak IEDF was predicted by the model; as the pressure increases to 20 mTorr, the double-peak IEDF gradually shifts to an IEDF with a strongly depleted high energy tail due to the higher ion-neutral collision frequency. The simulation results have good agreement with IEDF measurements. Further discoveries will be discussed. [Preview Abstract] |
Tuesday, October 6, 2020 4:15PM - 4:30PM |
KT2.00006: Electrostatic solitary waves in ion beam neutralization. Chaohui Lan, Igor Kaganovich The excitation and propagation of electrostatic solitary waves (ESWs) are observed in two-dimensional particle-in-cell simulations of ion beam neutralization by electron injection by a filament. Electrons from the filament are attracted by positive ions and bounce inside the ion beam pulse. Bouncing back and forth electron streams start to mix, creating two-stream instability. The instability saturates with the formation of ESWs. These ESWs reach several centimeters in longitudinal size and are stable for a long time ($\gg \tau_{b}$, the duration of the ion beam pulse). The excitation of large-amplitude ESWs reduces the degree of neutralization of the ion beam pulse. In addition, the dissipation of ESWs causes heating of neutralizing electrons and their escape from the ion beam, leading to a further reduction of neutralization degree. The appearance of these waves can explain the results of previous experimental studies, which showed poor ion beam neutralization by electro-emitting filaments. [Preview Abstract] |
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