The topic of the 2019 PPPS Minicourse is **Theoretical and Computational Methods in Plasma Physics**. This minicourse will be held June 22-23, 2019, which is the weekend prior to the main PPPS conference. The deadline to register for participation in the minicourse is **May 3, 2019**. Additional registration information will be posted here soon.

## Lectures

- Radha Bahukutumbi (LLE)
*Hydrodynamic simulations of High Energy Density Plasmas*

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### Abstract

High-energy density plasmas (typically defined as plasmas with pressures exceeding 1 Mbar) are found in many different contexts including planetary cores, inertial confinement fusion etc. High power lasers with powers above Tera Watts have been successfully used to generate and diagnose these conditions. In this lecture, the physics involved in generating and modeling these plasmas with lasers will be discussed. Multi-physics hydrodynamics codes include a large range of physics models spanning the interaction of the laser with the plasma, heat and radiation transport, static and transport material properties, and fluid flow. Typical models for these properties will be described. Comparison of simulation results with experiments will also be presented. Some aspects of high-energy density plasmas such as kinetic effects, laser plasma interactions are challenging to include in hydrodynamic codes. The limitations of modeling such plasmas with hydrodynamic approximations will be discussed.

### Biographical Summary

**Radha Bahukutumbi**
*Laboratory for Laser Energetics*

Radha Bahukutumbi is a Senior Scientist and Group Leader of the Integrated Modeling Group at the Laboratory for Laser Energetics at the University of Rochester. Her interests include Inertial Confinement Fusion, multi-physics modeling of high-energy density plasmas and nuclear physics. She has also taught courses on energy and environmental issues. Radha got her PhD from California Institute of Technology and has been working with radiation-hydrodynamic codes, and direct-drive fusion experiments on the OMEGA laser and the National Ignition Facility since. Radha is a fellow of the American Physical Society.

- Lee Collins (LANL)
*Quantum Mechanical Simulations of Warm, Dense Matter*

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### Abstract

The warm, dense matter regime (WDM), which ranges over densities from solid to hundreds of times compressed and temperatures from a few to hundreds of eV, spans a diverse range of environments including, as examples, planetary interiors of solar and exo- planets; stellar atmospheres; ICF implosions; and intense, short-pulse laser-solid interactions. Such environments consist of complex dynamical concoctions of atoms, molecules, ions, and free electrons in which quantum mechanical effects play a critical role. Several quantum many-body techniques such as Monte Carlo, Green’s functions, and molecular dynamics have shown considerable versatility in treating these extreme conditions and the strong quantum influences. In this tutorial, we shall explore WDM and hot plasma systems with a quantum molecular dynamics (QMD) as a representative approach that encapsulates the essential features of all the methods.. In the QMD, we solve the many-body Schrodinger equation for a large, representative sample of atoms, periodically replicated through space to effect the characteristics of a fluid, which may include a mixtures. For the electrons, we employ density- functional theory (DFT) in two guises: an orbital-based in the Kohn-Sham form and an orbital-free, usually in a Thomas-Fermi-Dirac approximation. This dual capability permits thorough coverage of these extreme conditions and provides a set of consistent static, dynamic, and optical properties such as equation of state (EOS), mass transport (viscosity/diffusion), opacity, and conductivity (thermal/electrical). We shall also discuss time-dependent (TD) formulations of both DFT approaches to calculate stopping power, conductivities, and interactions with electromagnetic fields.

### Biographical Summary

**Lee Collins**
*Los Alamos National Laboratory*

Areas of research:

Atomic, Molecular, and Optical Physics: interactions of electrons and photons with atoms and molecules, ultrafast laser processes, ultracold processes – BECs

Warm, dense matter and hot plasmas: static (equation-of-state), dynamical (diffusion/viscosity), and conduction properties of matter at extreme conditions Computational physics: development of methods to solve time-independent and time-dependent Schrodinger equations as well as those arising from density functional theory by large-scale simulation techniques. Molecular dynamics simulations of quantum and classical systems.

- Simon Cooke (US Naval Research Laboratory)
*Computational methods for modeling Vacuum Electronic and High-Power Microwave devices*

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### Abstract

This lecture will cover the physical models, equations and numerical methods that provide the foundations of modern simulation tools for Vacuum Electronic and High Power Microwave device design. Topics will include: electrostatic electron beam “gun” codes, time-domain electromagnetic particle-in-cell (PIC) codes, frequency-domain electromagnetic solvers, and custom “large-signal” design codes.

### Biographical Summary

**Simon Cooke**
*US Naval Research Laboratory*

Simon Cooke received the B.Sc. in Physics from the University of Strathclyde, Glasgow, Scotland, in 1988 and the D.Phil. degree from the University of Oxford, Oxford, England, in 1993. Since 1993 he has researched new computational methods to accurately model a broad range of electron-beam, plasma, and electromagnetic devices, at the University of Strathclyde, the University of Maryland, and with Science Applications International Corporation, McLean, VA until 2003. In 2003 he joined the Electromagnetics Technology Branch at the U.S. Naval Research Laboratory, Washington, DC, where he leads research into 3-D simulation algorithms to model complex RF and electron-beam devices. His current research interests include parallel electromagnetic particle-in-cell algorithms for GPUs, to enable fast, accurate design of advanced Vacuum Electronic amplifiers and High Power Microwave sources in the microwave to THz frequency range.

Dr. Cooke has been a Member of the IEEE NPSS since 1995 and Senior Member since 2012. He was a Guest Editor for the IEEE Transactions on Plasma Science Special Issue on High Power Microwaves in 2005 and for the IEEE Transactions on Electron Devices Special Issue on Vacuum Electronic Devices in 2014. He served on the IEEE NPSS Plasma Science and Applications Executive Committee between 2009 and 2011. In 2002 he was the recipient of the IEEE NPSS Early Achievement Award, in 2014 the Dr. Delores M. Etter Top Navy Scientists and Engineers of the Year Award, and in 2016 the Naval Research Laboratory Edison Chapter Sigma Xi Award for Pure Science.

- Allen Garner (Purdue U.)
*Microscale to Nanoscale Gas Breakdown: From Paschen’s Law to Schrödinger’s Equation*

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### Abstract

Historically, gas breakdown has been mathematically predicted by Paschen’s law based on the concept of the Townsend avalanche. Paschen’s law predicts that breakdown voltage increases without bound as the product of gap distance and gas pressure, pd, becomes large or small without bound and reaches a minimum at intermediate pd. Experimental studies as early as the 1950s noted deviations from this minimum breakdown voltage for microscale gaps at atmospheric pressure and hypothesized that they arose due to ion enhanced filed emission. These deviations become increasing important for microplasmas, where one desires a reproducible breakdown voltage at small scale, and in microelectromechanical and nanoelectromechanical systems where one strives to avoid gas breakdown for device reliability.

The drive toward even smaller electronics motivates a detailed analysis of all relevant electron emission mechanisms to optimize system design to either create or avoid plasma formation as applicable. Several studies have experimentally, computationally, and analytically demonstrated the transition from Paschen’s law to field emission at microscale. More recent studies have shown that further reducing gap size at a given pressure causes electron emission to transition from field emission to space-charge limited emission either with collisions (Mott-Gurney) or in vacuum (Child-Langmuir). Even smaller gap sizes cause space-charge limited emission to transition to Schrödinger’s equation. Moreover, the importance of the electrode surface structure on gas breakdown increases for submicroscale gaps, particularly the nonuniform electric fields that arise due to field enhancement or surface roughness and the implications of multiple breakdown events on electrode surface structure and subsequent breakdown events. This further motivates the development of Monte Carlo and molecular dynamics simulations to assess the impact of collisions on electron emission and breakdown mechanisms at these small scales.
This minicourse will provide a historical overview of the relevant breakdown and electron emission mechanisms, a theoretical perspective into their unification, and the implications of the transition between these mechanisms for various system parameters. The talk will also discuss the role of Monte Carlo simulations in feeding crucial physical parameters to each of these models apart from elucidating the electron dynamics in non-traditional operating regimes. Moreover, the integration and assessment of ongoing experiments at microscale and nanoscale to the theory and the extension of these theories and models to AC fields, particularly at microwave and terahertz frequencies, will be discussed.

### Biographical Summary

**Allen L. Garner**
*Purdue U.*

Allen L. Garner received the B.S. degree (with high honors) in nuclear engineering from the University of Illinois, Urbana-Champaign, in 1996. He received an M.S.E. in nuclear engineering from the University of Michigan, Ann Arbor, in 1997, an M.S. in electrical engineering from Old Dominion University, Norfolk, VA, in 2003, and a Ph.D. in nuclear engineering from the University of Michigan, Ann Arbor, in 2006.

He was an active duty Naval officer from December 1997 to December 2003, serving onboard the USS Pasadena (SSN 752) and as an instructor of the Prospective Nuclear Engineering Officer course at Submarine Training Facility, Norfolk VA. He is currently selected for promotion to Captain in the United States Navy Reserves. From 2006 to 2012, he was an electromagnetic physicist at GE Global Research Center, Niskayuna, NY. Since August 2012, he has been an Assistant Professor of Nuclear Engineering at Purdue University, West Lafayette, IN. His research interests include the application of pulsed power and plasmas for studies of biodielectrics, gas breakdown at microscale and nanoscale, and directed energy technologies. In 2016, he also served as a Summer Faculty Fellow at Air Force Research Laboratory at Wright-Patterson Air Force Base.
Prof. Garner received a University of Michigan Reagents’ Fellowship and a National Defense Science and Engineering Graduate Fellowship. He has been awarded two Meritorious Service Medals, the Navy and Marine Corps Commendation Medal, and five Navy and Marine Corps Achievement Medal. He was the Session Chair for the Biological, Medical, and Environmental session in the 2012 IEEE International Power Modulator and High Voltage Conference (IPMHVC), Publications Chair for the 2014 IPMHVC, Technical Chair for the 2016 IPMHVC, and Treasurer for the 2018 IPMHVC. He also received the 2016 IEEE NPSS Early Achievement Award. He is a licensed Professional Engineer in Michigan.

- Nicholas Ouart (US Naval Research Laboratory)
*Modeling non-LTE Plasmas for X-ray Spectroscopy*

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### Abstract

The x-ray radiation emitted by a non-LTE plasma can be used as a valuable tool for diagnosing its properties. Consequently, this can require detailed atomic physics models and a radiation transport method. This lecture will focus primarily on non-LTE atomic physics and radiation transport in 1-D using results from the NRL Drachma II code. Diagnostically analysis will be presented using isocontours of line ratios and powers.

### Biographical Summary

**Nicholas Ouart**
*US Naval Research Laboratory*

Nicholas Ouart received the B.S. degrees in electrical engineering and engineering physics in 2004 and the Ph.D. degree in physics in 2010 from the University of Nevada, Reno. He was a National Research Council Postdoctoral Research Associate at the Naval Research Laboratory (NRL). In 2012, he joined the staff of NRL. His research interests include plasma diagnostics and x-ray spectroscopy, high-energy-density plasmas, and radiation transport.

- Howard Scott (LLNL)
*Understanding and using non-LTE atomic and radiation kinetics for plasma modeling*

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### Abstract

This lecture will discuss issues and methods concerning the use of non-LTE kinetics in plasma modeling. Topics to be addressed will include characterization of plasma conditions for which non-LTE modeling is required and a survey of methods to fill that need. Radiation transport is often an important component of non-LTE modeling. The strong interactions between radiation and atomic kinetics produce strong numerical coupling, necessitating numerical methods tailored to reflect that coupling. Computational approaches for these coupled systems will also be discussed.

### Biographical Summary

**Howard Scott**
*Lawrence Livermore National Laboratory*

Howard Scott is a physicist at Lawrence Livermore National Laboratory, specializing in computational methods for non-LTE physics, radiation transport, plasma spectroscopy and large-scale simulations. He has authored or co-authored over 100 refereed articles and multiple book chapters. He has lectured at the International Centre for Theoretical Physics and has served as a consultant to the IAEA. He is the developer of the well-known non-LTE radiation transfer code Cretin.

Howard received his Ph.D. in astrophysics from Cornell University in 1982 with a thesis on accretion flows in active galactic nuclei. He then worked in the light ion fusion program at Sandia National Laboratories for two years before returning to astrophysics as a visiting faculty member at Virginia Tech. There he became interested in numerical approaches to multiphysics problems and began a computational effort, originally aimed at modeling accretion disk spectra, to efficiently combine atomic physics, radiation transport and hydrodynamics. In 1986, he brought those interests to LLNL where he has since applied them to numerous applications, including inertial confinement fusion, magnetic fusion, X-ray lasers, plasma spectroscopy, EUV lithography, and (occasionally) astrophysics. The original computational effort developed into the Cretin code and provides non-LTE capabilities to radiation-hydrodynamics codes at LLNL.

- Charles Seyler (Cornell University)
*Hall Physics in HED Plasmas: Methods and Results*

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### Abstract

Fluid models of plasma can have an enormous advantage over fully kinetic methods, such as the particle-in-cell methods, in the speed of numerical computation as well as for interpreting the results of simulations and experiments. The main limitation of fluid models is their domain of validity is restricted to collision-dominated phenomena. Assuming this is the domain of interest, then the question of what physics should one include in a fluid model becomes critically important. The magneto-hydrodynamical (MHD) model is the simplest model that retains the conservation laws of mass, momentum, and energy when properly formulated, and for this reason it is widely used to model many plasma phenomena. It is even used in parameter regimes that are well outside of its domain of validity due to its computational simplicity. When one must use a model that goes beyond MHD, the question becomes: how does one extend the MHD model while still retaining the computational advantages of a fluid description and the MHD model in particular? The Hall effect is manifested in a term in the Generalized Ohm’s law and is the most important extension of MHD to a class of models often referred to as Hall-MHD (HMHD) or extended MHD (XMHD). However, including the physics of the Hall term can significantly increase the computational complexity and dramatically decrease the speed of the computation. For these reasons, progress in the development of robust HMHD computational models has been slow. In this talk I will introduce the Hall-MHD model and discuss the difficulties in the development of efficient methods. As the main focus of the talk, I will discuss a method that we have used with great success that is both computationally simple and efficient when compared to most other methods for simulating Hall physics. I will show results of relevance to the high-energy density plasma regime that exemplify the importance of the Hall physics.

### Biographical Summary

**Charles Seyler**
*Cornell University*

Charles Seyler is a Professor of Electrical and Computer Engineering at Cornell University. Upon receiving his Ph.D from the University of Iowa in plasma physics he became a post-doctoral researcher in the Magneto-fluid Dynamics Division at the Courant Institute of Mathematical Science at New York University. He then went to Los Alamos National Laboratory to work in controlled fusion and in particular on the field reversed configuration (FRC). He came to Cornell in 1981 starting in magnetic fusion, but over the years he developed an interest in ionospheric and magnetospheric plasma phenomena and then in high-energy density (HED) plasmas. His current research focus is on development and application of efficient computational methods for simulating HED plasmas that include the notoriously difficult Hall effect.

- Brian Spears (LLNL)
*Deep learning: techniques for practitioners in the plasma sciences*

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### Abstract

Often without realizing it, we employ machine learning every day as we use our phones or drive our cars. Over the last few years, machine learning has found increasingly broad application in the physical sciences. This most often involves building a model relationship between a dependent, measurable output and an associated set of controllable, but complicated, independent inputs. The methods are applicable both to experimental observations and to databases of simulated output from large, detailed numerical simulations.

In this tutorial, we will present an overview of current tools and techniques in machine learning – a jumping-off point for researchers interested in using machine learning to advance their work. We will discuss supervised learning techniques for modeling complicated functions, beginning with familiar regression schemes, then advancing to more sophisticated neural networks and deep learning methods. Next, we will cover unsupervised learning and techniques for reducing the dimensionality of input spaces and for clustering data. We’ll show example applications from both magnetic and inertial confinement fusion. Along the way, we will describe methods for practitioners to help ensure that their models generalize from their training data to as-yet-unseen test data. We will finally point out some limitations to modern machine learning and speculate on some ways that practitioners from the physical sciences may be particularly suited to help. We will also share curated fusion simulation data and sample network code to provide practical tools for learning.

### Biographical Summary

**Brian Spears**
*Lawrence Livermore National Laboratory*

Brian Spears is a target design physicist in the inertial confinement fusion (ICF) program at Lawrence Livermore National Laboratory. His current work focuses on the intersection of experimental science, high-performance simulation, and machine learning. Brian leads a strategic initiative aimed at developing deep learning methods for improved scientific prediction. He has designed ICF experiments for almost 15 years, including the first cryogenic layered experiments at the National Ignition Facility. He developed new ICF ignition metrics using the first large-scale ensembles of 2D ICF simulations. Brian completed his PhD at the University of California, Berkeley where he studied topological methods for high-dimensional dynamical systems. He also holds a BS in mechanical engineering and a BA in liberal arts from the University of Texas at Austin. When not doing science, he can be found racing his bike or chauffeuring his two daughters to swim and gymnastics.

- Petros Tzeferacos (U. Chicago)
*A tutorial on HEDP modeling with FLASH: How to design and interpret laboratory experiments using numerical simulations*

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### Abstract

In this lecture a tutorial on high energy density physics (HEDP) modeling with the FLASH code will be presented. FLASH is a publicly available, high performance computing (HPC), adaptive mesh refinement (AMR), finite-volume radiation hydrodynamics and magneto-hydrodynamics code, with extended HEDP capabilities. This tutorial will cover the basic elements of the code’s capabilities and infrastructure, demonstrate with examples how to model HEDP laboratory experiments with FLASH, and showcase the importance of numerical modeling using as a case study recent breakthrough experiments conducted by Chicago and Oxford, which demonstrated fluctuation dynamo in a controlled laboratory environment for the first time.

### Biographical Summary

**Petros Tzeferacos**
*University of Chicago*

Dr. Petros Tzeferacos is a Research Assistant Professor at the Department of Astronomy & Astrophysics at the University of Chicago. He studied physics at the University of Athens in Greece and received his PhD in theoretical and computational plasma astrophysics from the University of Turin in Italy. Dr. Tzeferacos is the Director of the Flash Center for Computational Science, the vice chair of the High Energy Density Science Association (HEDSA), the vice chair of the Executive Committee of the National Ignition Facility User Group, and a member of the Omega Laser User Group (OLUG) Executive Committee. He is leading the development of the FLASH code, a publicly available multi-physics high-performance computing code that is widely used by the astrophysics and laboratory plasma research communities. Dr. Tzeferacos’ research focuses on plasma astrophysics and combines MHD theory, numerical modeling, and laser-driven laboratory experiments to study fundamental plasma processes in astrophysical objects. He has been a key participant in Discovery Science experimental campaigns at the National Ignition Facility, as well as in academic-led and laboratory-led experiments at the OMEGA laser facility at the Laboratory for Laser Energetics.

- Dale Welch (Voss Scientific)
*PIC methods and results in plasma simulations*

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### Abstract

Recent advances in implicit and hybrid techniques have demonstrated that finite-difference-time-domain particle-in-cell (PIC) simulation codes can effectively model volumetric and electrode plasmas at high density. Energy-conserving implicit kinetic algorithms greatly relax the spatial Debye length and temporal plasma frequency constraints allowing for larger simulations volumes and times. Including PIC hybrid techniques further accelerates the computational speed. These new capabilities allow for more accurate simulation of pulse-power accelerators, high power diodes, laser-plasma interactions, as well as magnetic and inertial confinement machines. In this course, we will explore PIC methodologies for kinetic, multi-fluid and quasi neutral fluid simulation. Hybrid techniques for blending the various PIC descriptions into a single integrated simulation will be discussed. Finally, practical usage of these techniques in stressing plasma physics environments will also be discussed.

### Biographical Summary

**Dale Welch**
*Voss Scientific*

Dr. Welch received his PhD in the simulation of inertial confinement fusion target at the University of Illinois (1985) where he developed implosion models for the study of shock-compression dynamics in laser-fusion experiments. This work centered on the modeling of laser-fusion implosions, diagnostics and simulation codes. While at Mission Research Corporation, Dr. Welch studied atmospheric electron beam propagation and ion beam transport in a fusion chamber assisting in the development of the 3D particle-in-cell codes Lsp and IPROP. Dr. Welch has made several contributions to the beam transport field involving advances in the simulation of density plasma, laser plasma interaction.

Dr. Welch joined Voss Scientific in 2005 where he serves as Computational Physics Division leader as well as principal investigator for multiple programs serving National Laboratories and Universities. He is involved with laser interaction with matter, fusion plasmas, charged-particle beam propagation in partially ionized gases, high-power particle beam accelerators and numerical analysis including the development of cutting edge plasma simulation tools. He is leading the development of the Chicago(TM) hybrid plasma simulation code focusing on advanced implicit techniques.