Bulletin of the American Physical Society
71st Annual Gaseous Electronics Conference
Volume 63, Number 10
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session TF4: Modeling and Simulation II |
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Chair: Trevor Lafleur, PlasmaPotential Room: Oregon Convention Center A107-A109 |
Friday, November 9, 2018 9:30AM - 10:00AM |
TF4.00001: Fluid modeling of transport and instabilities in magnetized plasma sources Invited Speaker: Gerjan Hagelaar Magnetized low-temperature plasma sources such as Hall thrusters or magnetrons involve complex transport phenomena which play a key role in their operation but are still not well understood, posing great challenges to both the development and the modeling of these sources. One of the main problems is the presence of various types of plasma instabilities, causing ``anomalous'' electron transport across the magnetic field lines. In this presentation, we discuss the capabilities and limitations of fluid models to describe transport in these magnetized plasma sources. We demonstrate that even very standard fluid models, when solved properly in the 2D plane perpendicular to the magnetic field lines, intrinsically produce certain plasma instabilities and anomalous transport. The behavior of these fluid instabilities may be more or less realistic in some cases but unphysical in others, depending on the plasma conditions and magnetic field configuration. Results are shown from a quasineutral fluid code based on standard equations for continuity, momentum and energy of (partially) magnetized electrons and ions, for different basic magnetized plasma source configurations. These results are compared with PIC simulations and linear stability analysis. [Preview Abstract] |
Friday, November 9, 2018 10:00AM - 10:15AM |
TF4.00002: Modelling of Negative Ion Production and Extraction from a Magnetized Plasma Source: insights from low density calculations Gwenael Fubiani, Jean-pierre Boeuf, Laurent Garrigues Negative ion sources are used in a wide variety of research fields and applications such as in tandem type electrostatic accelerators, cyclotrons, storage rings in synchrotrons, nuclear and particle physics and in magnetic fusion devices. In the latter, negative ions are generated mainly on cesiated metal surfaces as a byproduct of the bombardment of hydrogen or deuterium atoms. The ion source is magnetized and the plasma has typically an asymmetric profile [1]. In this work, we will discuss the physical mechanisms associated with the production and transport of negative ions both inside the plasma of a fusion-type ion source and the accelerator vessel [1,2], principally: (i) how does the plasma affect the extraction and properties of the negative ion beam? (ii) is it possible to model the ion beam transport with a lower plasma density, without any loss of generality? (a lower density relaxes the constraint of resolving numerically a micrometre size Debye length on a mesh and hence greatly speed-up the calculation) and lastly (iii) how does the plasma asymmetry affects the shape of the meniscus. The simulations are performed with a 2.5D Particle-in-Cell algorithm with Monte-Carlo Collisions (PIC-MCC). \\ \\$[1]$ G. Fubiani et al., New J. Phys. \textbf{19}, 015002 (2017)\newline \\$[2]$ G. Fubiani et al. Phys. Plasmas \textbf{25}, 023510 (2018) [Preview Abstract] |
Friday, November 9, 2018 10:15AM - 10:30AM |
TF4.00003: 2D PIC-MCC simulations of plasma dynamics across magnetic field lines: application to ROBIN negative ion source Bhaskar Chaudhury, Miral Shah, Mainak Bandyopadhyay, Arun Chakraborty The physics of plasma dynamics across strong magnetic field lines in negative ion sources is a complex phenomenon. The RF based negative ion source ROBIN (Rf operated Beam source in India for Negative ion research) has been setup at IPR, India to investigate the different issues related to production, transport and extraction of negative hydrogen ions in negative ion sources for fusion applications. The source consists of a driver, an expansion chamber, a magnetic filter and extraction grids. Magnetic filter plays an important role in reducing electron temperature inside the source, which is necessary to increase the negative ion yield. We require accurate computational models to completely understand the experimental results, and the complex plasma dynamics inside ROBIN. As a first step in this direction, we have developed an in-house parallel electrostatic 2D-3v PIC-MCC code to understand the collisional transport across magnetic filters under conditions similar to real ROBIN. Using this code, we have investigated different plasma characteristics such as plasma potential, electron temperature, electron and ion densities, current etc. as well as the effects of filter field on plasma transport. Several numerical experiments have been performed, and the simulation results show similar qualitative and quantitative behaviors as observed during the first phase of ROBIN experiments (without negative ions). [Preview Abstract] |
Friday, November 9, 2018 10:30AM - 10:45AM |
TF4.00004: On understanding of a magnetically enhanced hollow cathode arc plasma Liang Xu, Jens Peter Heinss, Denis Eremin, Peter Awakowicz, Ralf Peter Brinkmann Hollow cathode arc discharges have been studied for decades, particularly in the field of physical vapor deposition, but the underlying physics of these discharges is still not fully understood. In this work, the hollow cathode arc discharge with a strong axial magnetic field was investigated analytically and by means of particle-in-cell/Monte Carlo method. The models relate input parameters such as cathode geometry, magnetic field, discharge voltage, and feed gas flow rate with cathode electron emission, ionization, and particles fluxes. The dynamics of energetic electrons, i. e., cathode-emitted thermionic electrons after acceleration in the cathode fall, is studied by considering Coulomb collisions with Maxwellian bulk electrons and inelastic collisions with neutrals. The axial magnetic field within the cathode not only allows a discharge operation at a very low gas flow rate, but also presents a cross-field discharge in which the electron mobility decreases and instabilities may occur. The voltage-current and voltage-gas flow characteristics obtained by the analytical model are in good agreement with available experimental data. [Preview Abstract] |
Friday, November 9, 2018 10:45AM - 11:00AM |
TF4.00005: Particle-In-Cell Simulation of Planar Cylindrical Magnetron Sputtering Nathan Crossette, T. G. Jenkins, D. N. Smithe, J. R. Cary Magnetron sputtering is used in a variety of manufacturing processes for producing thin film coatings. Using VSim, a highly parallelized particle-in-cell/finite difference time-domain modeling code, we model the plasma environment and sputtering rate within a 2D axisymmetric cylindrical sputtering device. A static magnetic field from two annular magnets is used to confine particles, and Monte Carlo techniques simulate particle-background gas collisions. An external circuit model modulates the voltage on the target/cathode. We test the effects of varying the magnetic field strength, adjusting the configuration of the external circuit, and locations of the annular magnets on the plasma environment and erosion profiles. [Preview Abstract] |
Friday, November 9, 2018 11:00AM - 11:30AM |
TF4.00006: Quasineutral plasma modeling of low-frequency oscillations in cross-field discharge plasmas: breathing mode and rotating spokes Invited Speaker: Kentaro Hara Two types of low-frequency plasma oscillations that occur in cross-field discharge plasmas are presented. One is the breathing mode that is a discharge oscillation in the 10-30 kHz due to the interplay between ion acceleration and ionization. The other is azimuthally rotating spokes, self-organizing coherent structures that occur in the direction of the ExB drift of a cross-field discharge, such as Hall effect thrusters (HETs) and magnetron discharges. As much as a high-fidelity kinetic model is needed to understand the physics of such cross-field plasmas, a fluid type solver, particularly for electrons, is computationally inexpensive and useful for validation, namely, modeling low-frequency plasma oscillations that can be directly compared with experimental data. Fluid and hybrid fluid-kinetic models of cross-field discharge plasmas, assuming a quasineutral plasma and a drift-diffusion flux for electrons, are developed. First, numerical noise induced by nonlinear coupling due to the quasineutral assumption is reviewed and the development of an electron-pressure coupling method is discussed. Next, 1D axial simulations and perturbation theory of the HET discharge plasma are shown. The results indicate that electron transport and electron heat transfer play an important role in the excitation and damping of the ionization oscillations. Finally, stably propagating rotating spokes are simulated using a 2D axial-azimuthal hybrid simulation. It is suggested from the numerical results that the gradient drift instability downstream initiates an azimuthal nonuniformity, leading to low-frequency ionization oscillations in the azimuthal direction. [Preview Abstract] |
Friday, November 9, 2018 11:30AM - 11:45AM |
TF4.00007: Electron transport in a two-dimensional, hybrid-direct kinetic Hall thruster simulation Astrid Raisanen, Iain Boyd A two-dimensional, axisymmetric, hybrid-direct kinetic (DK) simulation of a Hall effect thruster channel and its near-field plume is capable of producing both steady and oscillating discharge current profiles, depending on the frequency of electron collisions with the channel walls and energy loss due to those collisions. This study attempts to improve the existing simulation and evaluate the effectiveness of different methods that have been proposed to model anomalous electron transport in Hall thrusters. The hybrid-DK algorithm uses an Eulerian approach to model the evolution of ions and neutral particles in discretized phase space, and due to its deterministic approach, it does not contain the statistical noise that is associated with Particle-in-Cell (PIC) methods. The two-dimensional simulation was recently benchmarked with a hybrid-PIC simulation, and there was good agreement overall. This work applies the DK simulation to an experimentally well-characterized thruster, improves simulation submodels including a more accurate implementation of an anode sheath, and applies different methods to model electron transport to ascertain their overall levels of utility. [Preview Abstract] |
Friday, November 9, 2018 11:45AM - 12:00PM |
TF4.00008: Asymptotic-preserving finite volume scheme for the multi-fluid equations towards electric propulsion applications Alejandro Alvarez Laguna, Thierry Magin, Pascal Chabert, Marc Massot, Anne Bourdon In this work, we introduce a numerical method for electric propulsion applications that solves for a fluid model that considers non-equilibrium, collisional, and anomalous transport processes. Previous fluid descriptions disregard some of these effects, whereas Particle-in-Cell (PIC) simulations are computationally very expensive and remain unaffordable to study full-domain geometries. The numerical method that is proposed here features a second-order finite volume discretization with an asymptotic-preserving scheme that is able to tackle the quasi-neutral behavior of the plasma without resolving the Debye length. Similarly, the scheme preserves the behavior of the fluids at different regimes of Mach number, similar to the one proposed by Alvarez Laguna et al.~(2016, 2018). These properties are found to be important to resolve the stiff system of equations that results from the large mass disparity between ions and electrons. Additionally, we analyze the numerical implications of discretizing the fluid set of equations for electric propulsion applications. The novel numerical model is benchmarked against PIC simulations obtained by LPPiC (Croes et al.~2017) and other fluid models that are available in the literature. [Preview Abstract] |
Friday, November 9, 2018 12:00PM - 12:15PM |
TF4.00009: Investigation of neutral depletion and propulsion performance in electrodeless RF plasma thrusters Yoshinori Takao, Kazuki Takase, Sora Yoshikawa, Kazunori Takahashi Electrodeless RF plasma thrusters, consisting of an RF plasma source and a magnetic nozzle, are one of the candidates for high-power and long-lifetime thrusters because no electrodes are exposed to the plasma for its generation or acceleration. However, significant axial momentum lost to the lateral wall of the source tube was detected in experiments when a high-density plasma was generated. This momentum loss seems to be due to the neutral depletion and the resultant axisymmetric profile of the plasma. Here, the effects of neutral depletion on plasma distribution and thruster performance are numerically investigated using a particle-in-cell simulation with Monte Carlo collisions (PIC-MCC) and the direct simulation Monte Carlo (DSMC) method, where the PIC-MCC and DSMC calculations are performed reciprocally to reproduce the neutral depletion and its effect on the plasma profile, depending on the different strengths of the external magnetic field. The numerical results have shown that both downstream gas injection and stronger external magnetic field lead to a shift of the plasma density peak from the upstream to the downstream side and a resultant larger total thrust, which qualitatively agrees with a previous experiment. [Preview Abstract] |
Friday, November 9, 2018 12:15PM - 12:30PM |
TF4.00010: A $z-\theta$ fluid simulation of a Hall Effect Thruster Valentin Joncquieres, Olivier Vermorel, Benedicte Cuenot With the renewed interest for Hall effect thrusters to supply light satellites, the industrial need for accurate numerical solvers has become crucial. To answer this demand, CERFACS is developing the AVIP-Fluid code which solves plasma physics in real industrial geometries using an unstructured parallel-efficient 3D fluid methodology. An AVIP-PIC version also exists which is presented in a separate contribution. Fluid models can provide in a reasonable computational time information about the plasma behavior inside the discharge channel. The present approach includes a detailed plasma model where each species is ruled by a system of Euler equations with source terms representing the electric field, ionization and other chemical processes. A Poisson equation is solved for the electric field. A particular attention is paid on specific numerical schemes implemented to deal with such equations in an unstructured and parallel formalism. The modeling of collision source terms is also investigated. After the presentation of models and numerics, a 2D $z-\theta$ simulation of a Hall thruster discharge channel is performed and compared to PIC simulations in order to observe the formation of the electron cyclotron drift instability. [Preview Abstract] |
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