C. David Turner

EMPHASIS/Nevada UTDEM User Guide Version 1.0

The Unstructured Time-Domain ElectroMagnetics (UTDEM) portion of the EMPHASIS suite solves Maxwells equations using finite-element techniques on unstructured meshes. This document provides user-specific information to facilitate the use of the code for applications of interest. UTDEM is a general-purpose code for solving Maxwells equations on arbitrary, unstructured tetrahedral meshes. The geometries and the meshes thereof are limited only by the patience of the user in meshing and by the available computing resources for the solution. UTDEM solves Maxwells equations using finite-element method (FEM) techniques on tetrahedral elements using vector, edge-conforming basis functions. EMPHASIS/Nevada Unstructured Time-Domain ElectroMagnetic Particle-In-Cell (UTDEM PIC) is a superset of the capabilities found in UTDEM. It adds the capability to simulate systems in which the effects of free charge are important and need to be treated in a self-consistent manner. This is done by integrating the equations of motion for macroparticles (a macroparticle is an object that represents a large number of real physical particles, all with the same position and momentum) being accelerated by the electromagnetic forces upon the particle (Lorentz force). The motion of these particles results in a current, which is a source for the fields in Maxwells equations.

Electromagnetic pulse excitation of finite- and infinitely-long lossy conductors over a lossy ground plane

Abstract This paper details a model for the response of a finite- or an infinite-length wire interacting with a conducting ground to an electromagnetic pulse excitation. We develop a frequency–domain method based on transmission line theory that we name ATLOG – Analytic Transmission Line Over Ground. This method is developed as an alternative to full-wave methods, as it delivers a fast and reliable solution. It allows for the treatment of finite or infinite lossy, coated wires, and lossy grounds. The cases of wire above ground, as well as resting on the ground and buried beneath the ground are treated. The reported method is general and the time response of the induced current is obtained using an inverse Fourier transform of the current in the frequency domain. The focus is on the characteristics and propagation of the transmission line mode. Comparisons with full-wave simulations strengthen the validity of the proposed method.

Validation and uncertainty quantification of ICEPIC/emphasis codes for a series of gas cell experiments at NRL

A series of gas-cell experiments were performed at NRL to be able to validate the dry air (as well as pure N2) chemistry/collision models available in Particle-in-Cell (PIC) codes. These experiments were constructed and performed with many diagnostics enabling comprehensive comparison between simulation and experiment. This multi-physics/stage problem (i.e. the pulse power circuit, cathode, foil, gas region and collection/anode) has diagnostics that can validate the simulation before and after each component. Because of the experimental access at each individual stage, this experiment is ideal for investigating the many models incorporated in various PIC codes. These measurements include the nonlinear coupling between each stage affecting the results both upstream and downstream of each measurement location. Therefore, these measurements are a stringent test of the models. In addition to numerical error, there is uncertainty of the parameters (e.g. the multi-group cross section used in the foil and the collision cross-sections used in the gas cell) in each component of the experiment. This study will examine the error propagated from one stage to the next; by accounting for these uncertainties we will be able to definitively validate the models. The experimental set up is a co-axial power feed which transitions to a disk-shaped cathode. The electron beam then passes through a thin anode foil which separates the vacuum diode from the gas cell; scattering and propagation in the foil is energy and angle dependent as calculated from ITS and SCEPTRE. The energy of the electrons going into the gas peaks at about 100 keV and the beam last for about 200ns. In addition to voltage and current measurements at various locations, the novel feature of these experiments is laser interferometry which measures the line-integrated electron density at various locations in the gas cell for a gas pressures ranging from 50 mTorr to 300 Torr.

Finite and infinite lossy conductors over a lossy ground plane excited by an electromagnetic pulse

We report a frequency-domain method based on transmission line theory that we name ATLOG — Analytic Transmission Line Over Ground — to model finite or infinite wires interacting with a conducting ground excited by an electromagnetic pulse. This method allows for the treatment of finite or infinite lossy, coated wires above a lossy ground, as well as resting on or buried beneath the ground. Comparisons with full-wave simulations strengthen the validity of the proposed method.

A Discontinuous Phase-Space Finite Element Discretization of the Linear Boltzmann-Vlasov Equation for Charged Particle Transport

We examine the modeling of charged-particle transport when both collision processes with background media and electromagnetic effects are important using the Boltzmann-Vlasov equation. We derive and transform the Boltzmann-Vlasov equation into a form very similar to the standard linear Boltzmann equation with additional operators. We apply the discontinuous finite element methods for discretization in the spatial, energy, and angular variables. An implementation of these methods demonstrates correct transport behavior for fixed electric and magnetic fields. We also demonstrate coupling to Maxwells equations with a simple electromagnetic solver to generate self-consistent fields.

Adaptive Mesh Refinement for Time-Domain Electromagnetics Using Vector Finite Elements: A Feasibility Study

This report investigates the feasibility of applying Adaptive Mesh Refinement (AMR) techniques to a vector finite element formulation for the wave equation in three dimensions. Possible error estimators are considered first. Next, approaches for refining tetrahedral elements are reviewed. AMR capabilities within the Nevada framework are then evaluated. We summarize our conclusions on the feasibility of AMR for time-domain vector finite elements and identify a path forward.

QUICKSILVER - a general tool for electromagnetic PIC simulation

The dramatic increase in computational capability that has occurred over the last ten years has allowed fully electromagnetic simulations of large, complex, three-dimensional systems to move progressively from impractical, to expensive, and recently, to routine and widespread. This is particularly true for systems that require the motion of free charge to be self-consistently treated. The QUICKSILVER electromagnetic Particle-In-Cell (EM-PIC) code has been developed at Sandia National Laboratories to provide a general tool to simulate a wide variety of such systems. This tool has found widespread use for many diverse applications, including high-current electron and ion diodes, magnetically insulated power transmission systems, high-power microwave oscillators, high-frequency digital and analog integrated circuit packages, microwave integrated circuit components, antenna systems, radar cross-section applications, and electromagnetic interaction with biological material. This paper will give a brief overview of QUICKSILVER and provide some thoughts on its future development.