John Loverich

Approximate Riemann solver for the two-fluid plasma model

An algorithm is presented for the simulation of plasma dynamics using the two-fluid plasma model. The two-fluid plasma model is more general than the magnetohydrodynamic (MHD) model often used for plasma dynamic simulations. The two-fluid equations are derived in divergence form and an approximate Riemann solver is developed to compute the fluxes of the electron and ion fluids at the computational cell interfaces and an upwind characteristic-based solver to compute the electromagnetic fields. The source terms that couple the fluids and fields are treated implicitly to relax the stiffness. The algorithm is validated with the coplanar Riemann problem, Langmuir plasma oscillations, and the electromagnetic shock problem that has been simulated with the MHD plasma model. A numerical dispersion relation is also presented that demonstrates agreement with analytical plasma waves.

A high resolution wave propagation scheme for ideal Two-Fluid plasma equations

Algorithms for the solution of the five-moment ideal Two-Fluid equations are presented. The ideal Two-Fluid model is more general than the often used magnetohydrodynamic (MHD) model. The model takes into account electron inertia effects, charge separation and the full electromagnetic field equations and allows for separate electron and ion motion. The algorithm presented is the high resolution wave propagation method. The wave propagation method is based on solutions to the Riemann problem at cell interfaces. Operator splitting is used to incorporate the Lorentz and electromagnetic source terms. To preserve the divergence constraints on the electric and magnetic fields two different approaches are used. In the first approach Maxwell equations are rewritten in their mixed-potential form. In the second approach the so-called perfectly hyperbolic form of Maxwell equations are used which explicitly incorporate the divergence equations into the time stepping scheme. The algorithm is applied to a one-dimensional Riemann problem, ion-acoustic soliton propagation and magnetic reconnection. In each case Two-Fluid physics described by the ideal Two-Fluid model is highlighted.

A Discontinuous Galerkin Method for the Full Two-Fluid Plasma Model

A discontinuous Galerkin method for the full two-fluid plasma model is described. The plasma model includes complete electron and ion fluids, which allows charge separation, separate electron and ion temperatures and velocities. Complete Maxwells equations are used including displacement current. The algorithm is validated by benchmarking against existing plasma algorithms on the GEM Challenge magnetic reconnection problem. The algorithm can be easily extended to three dimensions, higher order accuracy, general geometries and parallel platforms.

Modeling Radio Communication Blackout and Blackout Mitigation in Hypersonic Vehicles

A procedure for the modeling and analysis of radio communication blackout of hypersonic vehicles is presented. The weakly ionized plasma generated around the surface of a hypersonic reentry vehicle is simulated using full Navier–Stokes equations in multispecies single fluid form. A seven-species air chemistry model is used to compute the individual species densities in air including ionization: plasma densities are compared with the experiment. The electromagnetic wave’s interaction with the plasma layer is modeled using multifluid equations for fluid transport and full Maxwell’s equations for the electromagnetic fields. The multifluid solver is verified for a whistler wave propagating through a slab. First principles radio communication blackout over a hypersonic vehicle is demonstrated along with a simple blackout mitigation scheme using a magnetic window.

A Discontinuous Galerkin Method for Ideal Two-Fluid Plasma Equations

A discontinuous Galerkin method for the ideal 5 moment two-fluid plasma system is presented. The method uses a second or third order discontinuous Galerkin spatial discretization and a third order TVD Runge-Kutta time stepping scheme. The method is benchmarked against an analytic solution of a dispersive electron acoustic square pulse as well as the two-fluid electromagnetic shock (1) and existing numerical solutions to the GEM challenge magnetic reconnection problem (2). The algorithm can be generalized to arbitrary geometries and three dimensions. An approach to main- taining small gauge errors based on error propagation is suggested.

Time-domain simulation of nonlinear radiofrequency phenomena

Nonlinear effects associated with the physics of radiofrequency wave propagation through a plasma are investigated numerically in the time domain, using both fluid and particle-in-cell (PIC) methods. We find favorable comparisons between parametric decay instability scenarios observed on the Alcator C-MOD experiment [J. C. Rost, M. Porkolab, and R. L. Boivin, Phys. Plasmas 9, 1262 (2002)] and PIC models. The capability of fluid models to capture important nonlinear effects characteristic of wave-plasma interaction (frequency doubling, cyclotron resonant absorption) is also demonstrated.

Nonlinear full two-fluid study of m=0 sausage instabilities in an axisymmetric Z pinch

A nonlinear full five-moment two-fluid model is used to study axisymmetric instabilities in a Z pinch. When the electron velocity due to the current J is greater than the ion acoustic speed, high wave-number sausage instabilities develop that initiate shock waves in the ion fluid. This condition corresponds to a pinch radius on the order of a few ion Larmor radii.

Dynamic Electric Field Calculations Using a Fully Kinetic Ion Thruster Discharge Chamber Model

In this work, we present a fully kinetic particle-in-cell - Monte Carlo Collision (PIC-MCC) computer model developed to calculate the dynamic electric field inside an ion engine discharge chamber. This model self- consistently tracks primary electrons, secondary electrons, singly charged and doubly charged xenon ions, and xenon neutrals inside the discharge chamber. Both electric and magnetic field effects are included in the particle tracking. The plasma potential results are evaluated at every time step based on the charged particle distribution. This model avoids using an artificial inflated permittivity assumption and also avoids the use of the experimentally measured plasma potential data in the electric field calculations. Instead, a self-similar scaling system is considered. The computer model has been applied to study NASAs Next Generation Xenon Thruster (NEXT) operating at 5.3 kW, 3.1 A beam current, and 1567 V beam voltage. We discuss the recent algorithm development and present preliminary results such as the electric potential maps, the particle number density distributions, and the particle energy distributions from the NEXT ion thruster discharge chamber simulations.

Laboratory Modeling of the Plasma Layer at Hypersonic Flight

A simple approach to modeling the plasma layer similar to that appearing in the vicinity of a hypersonic vehicle is demonstrated in a laboratory experiment. This approach is based on the use of a hypersonic jet from a cathodic arc plasma. Another critical element of this laboratory experiment is a blunt body made from a fairly thin foil of refractory material. In experiments, this blunt body is heated by the plasma jet to a temperature sufficiently high to ensure evaporation of surface deposits produced by the metallic plasma jet. This process mimics reflection of gas flow from the hypersonic vehicle in a real flight. Two-dimensional distributions of the hypersonic plasma flow around the blunt body were measured using electrostatic Langmuir probes. Measured plasma density was typically 1012  cm−3, which is close to the values measured for real hypersonic flight. The demonstrated laboratory experiment can be used to validate numerical codes for simulating hypersonic flight and to conduct ground-based tests...

Fully Coupled Electric Field/PIC-MCC Simulation Results of the Plasma in the Discharge Chamber of an Ion Engine

In this paper simulation results for the plasma in the NASAs Evolutionary Xenon Thruster (NEXT) ion engine discharge chamber are presented. The unique aspect of these results is that the Poisson equation solution of the electric field is fully coupled with the particle tracking portion of the particle- in-cell Monte Carlo collision (PIC-MCC) model. This means the effects of charged particles on the electric field are accounted for in a precise, detailed manner. This fidelity of a simulation has never been performed for the plasma in the discharge chamber of an ion engine, until now. In the past, the present authors have presented results where the particle tracking portion of the PIC-MCC solution was weakly coupled to the electric field solution. This approximation was made to reduce the computational time from years to weeks. In this work, full coupling is simulated. The reason this full coupling can be performed in weeks of computational time, instead of years, is the self-similar scaling routine used and the convergence routines used. Many results for the plasma in the discharge chamber are presented in this paper including neutral, first ion, second ion, primary electron, and secondary electron number density distributions; as well as electron energy distributions and, of course, the electric potential distribution. These results are presented for the NEXT throttling level TL35. Our simulation results have been validated against experimental plasma measurements made on the laboratory model NEXT ion thruster at the University of Michigan. In addition, self-consistent ion bombardment sputter yield calculations were performed with our PIC-MCC model to compute the erosion profile of the cathode keeper face plate.