S. Copplestone

Parallel Performance of a Discontinuous Galerkin Spectral Element Method Based PIC-DSMC Solver

Particle based methods are required to simulate rarefied, reactive plasma flows. A combined Particle-in-Cell Direct Simulation Monte Carlo method is used here, allowing the modelling of electromagnetic interactions and collision processes. The electromagnetic field solver of the Particle-in-Cell method has been improved by switching to a discontinuous Galerkin spectral element method. The method offers a high parallelization efficiency, which is demonstrated in this paper. In addition, the parallel performances of the complete Particle-in-Cell module and the Direct Simulation Monte Carlo module are presented.

Complex-Frequency Shifted PMLs for Maxwell’s Equations With Hyperbolic Divergence Cleaning and Their Application in Particle-in-Cell Codes

The simulation of unbounded domains inevitably requires an artificial truncation of the computational domain and spurious reflections resulting from this procedure are a common problem. In this paper, a perfectly matched layer formulation for Maxwells equations in purely hyperbolic form is presented. The model is applied to standard wave attenuation problems and particle-in-cell simulations of electron beam devices.

Coupled PIC-DSMC Simulations of a Laser-Driven Plasma Expansion

In the field of material processing or spacecraft propulsion, laser ablation is used to remove material from a solid surface with a laser beam. The numerical study of this process has been directed towards direct laser-solid interactions, tackled by molecular dynamics simulations which have been conducted in the past. An additional field of interest arises, when considering the interaction of a laser beam and the plasma created by former laser impacts. For this purpose, an Message Passing Interface parallelized, high-order Particle-in-Cell scheme coupled with a Direct Simulation Monte Carlo method is used to handle the complex phenomena, which usually are simulated using disjoint techniques. The complete scheme is constructed to run on three-dimensional unstructured hexahedra, where for the Particle-in-Cell solver, a highly efficient discontinuous Galerkin method is used to calculate the electromagnetic field. Simulations under realistic settings require the use of high performance computing, where the parallel performance of the coupled solver plays the most important role. This work offers insight into such an undertaking by simulating the expansion of a plasma plume in three dimensions using this coupled algorithm.

Comparison of plasma plume expansion simulations using fully kinetic electron treatment and electron fluid models

The expansion of a plasma plume resulting from laser ablation plays an important role in a large number of applications, e.g., material processing, medical laser applications or novel space propulsion concepts. Here, a high-order three-dimensional Particle-In-Cell code is used to simulate such a plasma plume expansion. A major challenge in this kind of simulation is the handling of the electrons due to their low inertia and resultant high acceleration. Therefore, two separate treatments of electron modeling are compared. Firstly, the electrons are simulated as a normal particle species in a kinetic manner, which strongly decreases the time step size and thereby increases the computational effort. Secondly, the electrons are simulated using an electron fluid model that reduces the computational cost but is less accurate [1]. Additionally, the results from the fully kinetic model are compared regarding chemical reactions, in this case ionization and ion recombination. The electron potential is solved using ...

Recent developments of DSMC within the reactive plasma flow solver PICLas

In order to enable the numerical simulation of rarefied plasma flows in thermal and chemical non-equilibrium, electro-magnetic interactions as well as particle collisions have to be considered. A common approach is to use particle-based methods. The Particle-in-Cell (PIC) method simulates charged collisionless gas flows by solving the Vlasov-Maxwell equation system while particle collisions in neutral reactive flows are treated by the Direct Simulation Monte Carlo (DSMC) method. Therefore, PICLas is being developed, a coupled simulation code that enables three-dimensional particle-based simulations combining high-order PIC and DSMC schemes for the simulation of reactive, rarefied plasma flows. PICLas enables time-accurate simulations on unstructured hexahedral meshes and is parallelized for high-performance computing. In addition to an overview of PICLas, the current development status of the DSMC module is presented. This includes the relaxation of polyatomic gases, the extension of the chemical modeling...

A particle localization algorithm on unstructured curvilinear polynomial meshes

Abstract Many particle-based methods require a coupling between particle motion and fluid flows or fields. The particle motion is approximated in phase space, while the fluid flows or fields are calculated on a fixed Eulerian frame of reference. In this work, we present algorithms for locating and tracing particles through curvilinear and unstructured hexahedral meshes. Special attention is given to accurately compute the intersections of particles with polynomial curvilinear faces. We derive two localization algorithms, which locate particles either by tracing in physical space or restricting the tracing step to boundary faces and determining the particles position in reference space. The proposed algorithms are validated by three-dimensional charged particle simulations in electromagnetic fields.

PIC-DSMC simulations of plasma plume expansions with ionization and recombination processes

Summary form only given. Laser ablation of metals has numerous applications, ranging from material processing to spacecraft propulsion. The impacting laser generates a plasma plume in front of a surface that expands into vacuum or a background medium. Different effects within the expanding plume are responsible for charge separation and particle acceleration, which fundamentally affect the expansion characteristics that are important for subsequent laser-plasma interactions. State-of-the-art simulation codes couple methods that handle charged particles as well as particle collisions with chemical reactions in different forms. Therefore, a high-order, three-dimensional Particle-In-Cell (PIC) method for simulating charged particle flows is coupled with a Direct-Simulation-Monte-Carlo (DSMC) scheme, which handles collisions between particles in a stochastic manner. Possible chemical reactions that occur at different stages within plasma plume are modeled on a microscopic level by employing the recently developed Q-K model.

Complex-frequency shifted perfectly matched layers with respect to particle treatment in a particle-in-cell scheme

Summary form only given. Computational simulation of low-density plasma physics demands a high amount of accuracy and efficiency when considering complex particle-field interactions. The modeling of unbounded domains around sources of electromagnetic radiation inevitably requires the artificial truncation of the computational domain at a certain point, which leads to spurious reflections, because the truncation itself is not present in the physical model. To tackle these reflections, a high-order, three-dimensional particle-in-cell method is adapted. Charge conservation is enforced by hyperbolic divergence cleaning. A Discontinuous Galerkin (DG) spectral element method treats the time-dependent Maxwell equations on unstructured meshes. Additionally, a complex-frequency shifted2 Perfectly Matched Layer1 (PML) technique for the Maxwell system with respect to the hyperbolic charge correction is derived. This leads to an additional set of ordinary differential equations within the PML region, which is treated by the same DG scheme. Together with a mesh-free particle pusher in Lagrangian fashion, the Maxwell-Vlasov system is advanced in time by standard Runge-Kutta schemes.