Shumlak, UriTaheri, Sina2021-10-292021-10-292021-10-292021Taheri_washington_0250E_23449.pdfhttp://hdl.handle.net/1773/47907Thesis (Ph.D.)--University of Washington, 2021Interaction between plasma fluid and neutral species is of great importance in the dynamic behavior of magnetically confined plasma devices, such as the edge region of tokamaks and the plasma formation of Z-pinches. The presence of neutrals can have beneficial effects such as fueling burning plasmas and quenching the disruptions in tokamaks, as well as deleterious effects like depositing high energy particles on the vessel wall. Also, it can affect the stability of a pinch and change the dynamics of the pinch collapse. Thus, incorporation of atomic physics with plasma modeling tools is required to study next-generation fusion devices. Fluid-based plasma models such as magnetohydrodynamic (MHD) are commonly used for fusion simulation. One of the key challenges in numerical simulation with these fluid models is the vast separation of the time scales describing different physics in the model. The semi-implicit leapfrog time advance scheme is one of the commonly used algorithms for initial-value problems that can bridge between fast-wave and slow-diffusive time scales. Functional structure of the MHD equations results in a data dependency among fields and lets the advances for the plasma density, velocity, temperature, and magnetic field to be staggered and solved sequentially. Inclusion of the atomic interactions between plasma and neutral species breaks the data dependency in MHD equations and also adds more to an already vast span of time scales. A reacting plasma-neutral model [E. T. Meier, and U. Shumlak. ``A general nonlinear fluid model for reacting plasma-neutral mixtures." Physics of Plasmas 19.7 (2012): 072508] is used to study the interaction between plasma and neutral fluids that accounts for electron-impact ionization, radiative recombination, and resonant charge exchange. In this research we address how to best integrate atomic physics into semi-implicit leapfrog time advance. Two competing approaches are studied: 1) Crank-Nicolson time-centering of the atomic reactions within the framework of leapfrog algorithm. A Newton iteration is used to include nonlinear terms in atomic physics. 2) Operator-splitting the terms associated with the atomic interactions into constituent ODE and PDE parts using a Strang-splitting technique. As a variation to this splitting method a Douglas-Rachford inspired splitting scheme is considered as well. Accuracy and efficiency of the time-advance methods are studied through a series of zero- and one-dimensional test cases. Among the 0-D cases we compare the shear Alfv\'en and magneto-acoustic wave propagation results with analytic solutions where all other cases are compared to a fine-time-resolution base calculation. We consider two 1-D examples: fusion-plasma edge fueling representing a slow dynamic application and a planar electromagnetic plasma accelerator as a fast wave application. We show that a second-order-in-time Douglas-Rachford inspired coupling between the ODE and PDE advances is effective in reducing the time-discretization error to be comparable to that of Crank-Nicolson with Newton iteration of the nonlinear terms. Splitting ODE and PDE parts results in independent matrix solves for each field which reduces the computational cost considerably and provides parallelization over species relative to Crank-Nicolson.application/pdfen-USnoneComputational Plasma PhysicsMagnetoHydroDynamicsNeutralsPlasma PhysiscsPlasma physicsAeronautics and astronauticsThesis