Talk Title: Studying gas puff Z-pinches experiments on CESZAR with FLASH. Towards designing ZEBRA experiments.

Abstract: Gas puff Z-pinches [1] have been studied for decades, with different variations on the materials and dimensions of the setup, to make it more stable and better suited for fusion. Previous experiments on the CESZAR platform [2] have demonstrated different behaviors of the pinch depending of the presence and the material used for the target. Here, we show that the new capabilities of the FLASH code have made it possible to simulate such setups in 2D, capturing the development of the Rayleigh Taylor instability (RTI), that we first validated with HYDRA comparisons [3]. Then, we took advantage of the AMR implementation to reproduce CESZAR experiments and thus validate FLASH with experimental data, also shedding light on the underlying RTI mitigation mechanism at stake [4]. Finally we designed, for the first time with FLASH, gas puff Z-pinches experiments to be conducted next fall on ZEBRA, based on previous experiments conducted by F.Conti [5]. They aim at studying the effects of liner radius on the pinch stability, a study suggested by the recent results obtained on the Double Eagle facility that suggests strong shock heating could mitigate RTI for particularly extended liners [6]. We obtained numerically a trend for RTI growth rate with respect to the liner radius, while taking a deeper look at the mitigation process during the implosion. These results, if validated experimentally, would show that the FLASH code is now suited to design gas puff Z-pinches experiments in the future.

We acknowledge support by the Department of Energy (DOE) National Nuclear Security Administration (NNSA) under award numbers DE-NA0004144, and DE-NA0004147, under subcontracts no. 536203 and 630138 with Los Alamos National Laboratory, and under subcontract B632670 with Lawrence Livermore National Laboratory. We acknowledge support from the U.S. DOE Advanced Research Projects Agency-Energy (ARPA-E) under Award Number DE-AR0001272 and the U.S. DOE Office of Science under Award Number DE-SC0023246.

REFERENCES

[1] M.G.Haines, “A review of the dense z-pinch” Plas. Phys. Contr. Fusion (2011).

[2] Conti, F., et al. "MA-class linear transformer driver for Z-pinch research." Physical Review Accelerators and Beams 23.9 (2020).[3] D. Michta et al., “Gas-puff Z-pinch modelling with the FLASH code”, soon to be submitted (2024)

[4] A. Williams et al., to be submitted (2024).

[5] Conti, F., et al. "Study of stability in a liner-on-target gas puff Z-pinch as a function of preembedded axial magnetic field." Physics of Plasmas 27.1 (2020).

[6] E. Ruskov et al. "Staged Z-pinch experiments and modelling on the 4 MA pulsed power generator Double Eagle." APS Division of Plasma Physics Meeting Abstracts (2023).

Bio: I am a french Postdoctoral Associate who obtained his Ph.D. in Physics and Astrophysics from the Sorbonne University in Paris, France, where he worked on radiation waves and mathematical modeling of new classes of laboratory astrophysics experiments. I am now part of the FLASH center, working on high energy density physics phenomena often involving the study of radiation effects wether it is on astrophysical scale or in the laboratory. Recently, my main interest has been on gas puff Z-pinches and radiation-matter coupling in those systems, with a focus on shocks and Rayleigh Taylor instability dynamics.

Talk Title: Ice Giant Interiors and Magnetic Fields

Abstract: There is still considerable ambiguity in the exact structure, composition, and thermal profile of ice giant planets Uranus and Neptune. While these planets are assumed to be primarily composed of complex mixtures of water, methane, and ammonia, the material properties of these mixtures are poorly known. As a result, there is no interior model of Uranus and Neptune based on material properties which adequately matches observed heat fluxes, magnetic fields, and gravitational fields simultaneously. My research focuses on calculating and applying equations of state and transport properties for water, methane, ammonia, and their mixtures using ab initio and machine learning simulations. My first project involved studying superionic phases of these materials at extreme temperatures and pressures, in which protons diffuse like a liquid through stable lattices of heavier nuclei. Through this work, we observed a novel state of matter: double superionicity. I am working further to develop dynamo models for ice giant planets, that fully represent the radial dependence of the parameters I calculate. In doing so, I seek to constrain the interior profile, compositions, and pressure/temperature conditions of Uranus and Neptune to provide a complete model of these planets' interiors. 

Bio: Kyla is a Ph.D. student to the Earth and Planetary Science Department at UC Berkeley! She is intrigued by the application of quantum mechanical calculations to study the properties of materials at high temperatures and pressures, such as in planetary interiors.

Title: Accelerating Analysis of Laboratory Astrophysics Experiments with Simulations and Deep Learning

Abstract: Laboratory experiments are the key component of developing our understanding and supporting the theory behind astrophysical phenomena. Simulations are often used to model these experiments and help gain insight into the data analysis. As datasets and simulations grow in complexity and size, it can become challenging to use conventional analysis methods. This talk investigates how deep learning can be used to help accelerate the analysis of laboratory astrophysics experiments. The work focuses on training neural networks to analyze ion acoustic wave (IAW) features from simulated Thomson scattering images and compares results with common analysis methods.

Bio: Michael is a Ph.D. student at UC San Diego, working under advisor Dr. Alexey Arefiev, and a graduate student at CMEC. He is a member of the Alfred P. Sloan Foundation’s Minority Ph.D. program and in the Lawrence Livermore National Laboratory Academic Cooperation Program. His research interests include data science and artificial intelligence applications in high energy density physics, laboratory astrophysics, and computational physics.

Title: Turning up the Heat on High Energy Density Materials in Silico — Case Studies

Abstract: Not Available

Bio: Dr. Zhang received a B.S. in Optical Information Science and Technology from Harbin Institute of Technology in 2008, a Master’s degree in Condensed Matter Physics from Peking University in 2011, and a Ph.D. in Earth and Planetary Science from the University of California at Berkeley in 2016. After a short-term postdoc at UC-Berkeley, he joined the Quantum Simulation Group at Lawrence Livermore National Laboratory as a postdoctoral research staff member in 2017 and worked there until joining LLE in 2019. His research is mainly in using theoretical tools to elucidate the extreme physics of matter that are relevant to high-energy-density experiments, inertial confinement fusion, and Earth and planetary science applications. The tools include state-of-the-art path integral Monte Carlo, auxiliary field quantum Monte Carlo, density functional theory, and first-principles molecular dynamics, among others.

Title:  Mixing Matters: Revealing Rock-Ice Miscibility in Massive Water World Interiors

Abstract:  Understanding the interior structure and composition of super-Earths and sub-Neptunes, which lack direct analogs in our solar system, is crucial for unraveling their formation, evolution, and geophysical properties. Dynamic material interactions at extreme pressures and temperatures play a pivotal role in comprehending these planetary interiors. Water worlds are generally characterized by a massive water layer overlaying a rocky mantle and iron core. In this study, we investigate the miscibility of rock materials bridgmanite (MgSiO3) and magnesium oxide (MgO) with water (H2O), all abundant materials in planetary formation. Density functional molecular dynamics (DFT-MD) simulations allow us to explore the conditions necessary for rock-ice miscibility within the interiors of water worlds. Covering a range of pressures (30-200 GPa) and temperatures (500-8000 K), our simulations reveal that rock and ice mix under conditions reached during graze and merge collisions, as confirmed by smoothed particle hydrodynamic simulations. These findings have significant implications for planetary evolution, as they indicate the presence of compositional gradients that impact convection and heat transport as water-rich planets cool. Moreover, our study calls for a reassessment of models assuming fully adiabatic interiors for water-rich worlds.

Bio: Tanja is a graduate student at UC Berkeley under advisor, Burkhard Militzer.  Her research interests include: planetary interiors, planetary formation, ab initio molecular dynamics, density functional theory simulations. 

Title:  TInvestigations of Phase Transitions and Metastability using Ultrafast Diffraction under Dynamic Loading

Abstract:  Combining dynamic compression with pulsed X-ray probes enables the investigation of a material's structural response to high-strain rate loading. Laser-driven experiments at XFEL, synchrotron, and high-power laser facilities allow us to explore crystallographic phase transitions and melting under nanosecond loading and release and identify under what conditions (pressure, temperature, strain rate) we observe phase transitions to stable and metastable phases. This talk will review recent in situ diffraction studies of carbides, oxides, and transition metals under laser-based shock and ramp compression. These studies demonstrate that high-pressure phase transitions can be explored on nanosecond timescales, improving our understanding of the high-pressure-temperature phase stability of materials and their time-dependent, metastable phase diagrams.

Bio: Sally June Tracy is interested in materials in extreme environments with applications to both mineral physics and materials science.

Sally June Tracy and her research group use high-pressure-temperature experiments to explore the physical properties and phase stability of materials under extreme conditions up to and exceeding those at the center of the Earth. This includes studies of crystal structures, phase stability, elasticity, and deformation behavior. 

Her main tools include laser-drive and gas-gun dynamic compression coupled with laser interferometry and X-ray probes. Additionally, we use diamond-anvil cells combined with synchrotron X-ray scattering to investigate the crystal structure, lattice dynamics, and spin state of materials under static high-pressure and temperature conditions. This work provides experimental constraints on subjects ranging from planetary formation, high-pressure phases of deep planetary interiors, and materials for extreme applications. 

Title:  Thermodynamics of Planetary Building Blocks

Abstract:  Temperature is an incredibly useful metric for better understanding material behavior and phase changes induced by shock compression, as well as post-shock states. In particular for silicates, insight on the processes of planetary formation and evolution benefit greatly with in-situ shock temperature measurements. First, we performed experiments on quartz and fused silica at the UC Davis Shock Compression Lab probing the region where these materials undergo shock melting and superheating. Second, we have two recent campaigns on the Sandia Z Machine and OMEGA EP laser establishing the principal Hugoniot on the pyroxenes enstatite and bronzite and a pyrolitic composition glass, focusing on temperature analysis with colored and Fe-bearing samples. These projects span a wide range of pressures and show the utility of shock experiments at a variety of P-T regimes.

Bio: Kaitlyn Amodeo is a 6th year PhD student at UC Davis working with Sarah Stewart. Her research focuses on shock compression experiments on minerals measuring temperature. This summer, she will be starting a postdoc at Sandia National Laboratory.

Title:  Simulating Shock in Silicon and Diamond Carbon

Abstract:  Silicon and Diamond Carbon are both materials of interest in the scientific and industrial areas of research. Silicon is a widely used material in many commercial applications, but also has a large number of experimental and simulated research performed on it due to the ease with which large single crystalline samples can be created. Diamond carbon is another important material for many applications, such as the material of choice for the capsules which held the fuel in the recent National Ignition Facility Inertial Fusion efforts that managed to reach net positive ignition. To better understand these materials, my research has focused on exploring the behavior of these materials when subjected to shocks, modeling phase transformations and dislocation emissions through the use of computational simulations.

Bio: Alex Li is a 4th year PhD student at UC San Diego under Professor Marc Meyers. He got his undergraduate degree from UC Berkeley and his master's degree from Columbia University, all studying the subject of Materials Science and Engineering. He has been working with Dr. Rob Rudd from Lawrence Livermore National Labs and has been attending the Computational Chemistry and Materials Science Internship Program hosted by the lab for the past several years.

Title:  Interface dynamics in ideal and realistic fluids

Abstract:  Interface and mixing and their non-equilibrium kinetics and dynamics couple micro to macro scales, and are ubiquitous to occur in fluids, plasmas and materials, in high energy density regimes. Stellar evolution, plasma fusion, reactive fluids, purification of water, and nano-fabrication are a few examples of many processes to which dynamics of interfaces is directly relevant. This talk presents the rigorous theory of the stability of the interface – a phase boundary broadly defined. We directly link the structure of macroscopic flow fields to microscopic interfacial transport, quantify the contributions of macro and micro stabilization mechanisms to interface stability, and discover the fluid instabilities never previously discussed. In ideal and realistic fluids, the interface stability is set primarily by the interplay of the macroscopic inertial mechanism balancing the destabilizing acceleration, whereas microscopic thermodynamics create vortical fields in the bulk. By linking micro to macro scales, the interface is the place where balances are achieved.

Bio: Snezhana Abarzhi is theoretical physicist and applied mathematician specializing in the dynamics of fluids and plasmas and their applications in nature and technology. Her key results are the mechanism of interface stabilization, the special self-similar class in the interfacial mixing, and the fundamentals of Rayleigh-Taylor instabilities. Her key contributions to the community are the program ‘Turbulent Mixing and Beyond’ and the editorial work. Her achievements are recognized nationally and internationally (by, e.g., National Science Foundation and National Academy of Sciences in the USA, Japan Society for Promotion of Science in Japan, Alexander von Humboldt Foundation in Germany). She is elected Fellow of the American Physical Society (APS) for ‘for deep and abiding work on the Rayleigh-Taylor and related instabilities, and for sustained leadership in that community’. She serves the APS Committee on Scientific Publications. Snezhana I. Abarzhi is professor and chair of Applied Mathematics at the University of Western Australia. Before that she worked at Carnegie Mellon University, the University of Chicago, Stanford University, and SUNY Stony Brook in the USA, and at the Osaka University in Japan, and the University of Bayreuth in Germany.

Title: Extreme Material Dynamics Experiments on SNL’s Z Machine

Abstract:  Cutting edge shock compression research is moving towards ever increasing pressure or stress states into the terapascal range. The SNL Z machine is an “engine of discovery” for high energy density science. Shock experiments on Z are advancing understanding the high P-T behavior of materials and the measurement of accurate equation of state models based on experimental data. This talk will review how shock experiments are done on the Z machine and will focus on three examples of materials shock compressed into the terapascal range: the PMMA polymer, the Pt pressure standard, and the Ti64 alloy.

• https://journals.aps.org/prb/accepted/3c07cO90J741fd4061ee3b303fa03d1fb33f395c3
• https://journals.aps.org/prb/abstract/10.1103/PhysRevB.105.224109#
• https://aip.scitation.org/doi/10.1063/5.0128681

Bio: Pat Kalita is a physicist at SNL and the PI of several experimental campaigns on the Z machine. She also leads cross-platform projects on the kinetics of dynamically driven phase transitions.  She previously spoke in this series about dynamic x-ray diffraction and kinetics of shock processes.

Title: New Lens on the Frontier Matter in Extreme Conditions

Abstract:  The study of matter under extreme conditions is a highly interdisciplinary subject with broad applications to materials science, plasma physics, geophysics and astrophysics. Understanding the processes which dictate physical properties in warm dense plasmas and condensed matter, requires studies at the relevant length-scales (e.g., interatomic spacing) and time-scales (e.g., phonon period). Experiments performed at XFEL lightsources across the world, combined with dynamic compression, provide ever-improving spatial- and temporal-fidelity to push the frontier. This talk will cover a very broad range of conditions, intended to present an overview of important recent developments in how we generate extreme environments and then how we characterize and probe matter at extremes conditions– providing an atom-eye view of transformations and the fundamental physics dictating materials properties. Examples of case-studies closely related to geophysics, astro(bio)physics, planetary-, and fusion energy-sciences, as enabled by microstructure visualization from in situ, ultrafast X-ray imaging, diffraction and spectroscopy will be discussed.

Bio: Arianna Gleason received her Ph.D. in Earth and Planetary Science from the University of California, Berkeley in 2010. She joined Stanford University as a postdoctoral scholar in 2010 and then worked for Los Alamos National Laboratory in the Shock and Detonation Physics group before joining SLAC National Accelerator Laboratory as a staff scientist in 2018. Her work focuses on visualizing materials behavior and response across all length-scales at the most extreme environments possible in nature – from depths of the Earth’s crust to planetary cores and even stellar interiors. Her studies center on high-pressure mineral physics and planetary evolution from the atomic level up. In 2019 she received the Department of Energy’s Early Career Award from the Office of Science, Fusion Energy Science.

Title: Phase Behavior of Water and Hydrocarbons at Planetary Conditions

Abstract: Water and hydrocarbons are important building blocks in the Outer Solar System. Most of the water in the universe may be in a superionic state, and its thermodynamic and transport properties are crucial for planetary science but difficult to probe experimentally or theoretically. Hydrocarbon mixtures are also extremely abundant in the Universe, and diamond formation from them can play a crucial role in shaping the interior structure and evolution of planets. We use machine learning and free energy methods to overcome the limitations of quantum mechanical simulations and study the high-pressure phase behavior of these systems. For water we predict that close-packed superionic phases are stable over a wide temperature and pressure range, while a body-centered cubic superionic phase is only thermodynamically stable in a small window but is kinetically favored. Our phase boundaries, which are consistent with the existing-albeit scarce-experimental observations, help resolve the fractions of insulating ice, different superionic phases, and liquid water inside of ice giants. In the case of hydrocarbons, with first-principles accuracy, we first estimate the diamond nucleation rate in pure liquid carbon, and then reveal the nature of chemical bonding in hydrocarbons at extreme conditions. We finally establish the pressure-temperature phase boundary where diamond can form from hydrocarbon mixtures with different atomic fractions of carbon. Notably, we find a depletion zone in Neptune (but not Uranus) where diamond formation is thermodynamically favorable regardless of the carbon atomic fraction, due to a phase separation mechanism. These findings can lead to a better understanding of the physics of planetary formation and evolution, and help explain the dochotomy between Uranus and Neptune.

Bio: Dr. Sebastien Hamel is a physicist in the Physics and Life Sciences Directorate at Lawrence Livermore National Laboratory. He earned his Ph.D. in Physics in 2003 and his M.S. in Astrophysics in 1998 from the University of Montreal in Canada. After working as a post-doctoral researcher in Ecole Polytechnique in Montreal, Canada he was hired as a post-doctoral researcher at LLNL in 2005 and became a permanent member of the scientific staff in 2008. He is a main contributor to the equation of state effort at LLNL both on the theory side and as part of experimental teams where he uses quantum chemistry and other simulations to aid in the interpretation of experimental data. His interests include using large-scale parallel Monte-Carlo, classical and quantum molecular dynamics computations and deep learning algorithms to address issues in planetary science, in inertial confinement fusion and in projects centered on the structural, optical and transport properties of nanostructures and molecular crystals. He has led NASA and LDRD projects at LLNL and received a R&D100 Award for the invention of the first plastic scintillator for neutron and gamma discrimination.

Title: Disentangling Cosmic Magnetic Field Generation: From Laser-target Illumination in the Laboratory, to Ray-tracing on the Computational Domain

Abstract: The Weibel instability and the Biermann battery are two out of several mechanisms proposed to explain astrophysical seed magnetic fields in our Universe. The experiments performed by the Astrophysical Collisionless Shock Experiments using Lasers (ACSEL) Team at the Omega Laser Facility of the Laboratory for Laser Energetics, and those carried out by the Phoenix Laboratory at UCLA using the Peening laser have reproduced and measured both of these mechanisms respectively. In this talk I present numerical simulations that have modeled these two experimental campaigns using the multi-physics, magnetohydrodynamics (MHD), adaptive mesh refinement code FLASH. I discuss how we can use MHD simulations to interpret the plasma properties and the physical mechanisms occurring in such experiments. Furthermore, I demonstrate how experiments can be used to validate numerical implementations by example of the Biermann term in FLASH. This work illustrates how concerted modeling and experimental efforts can shed light on magnetogenesis within the context of laboratory astrophysics.

This work was supported by the U.S. Department of Energy (DOE) National Nuclear Security Administration (NNSA) under Award Numbers DE-NA0003842 (Center for Matter at Extreme Conditions, CMEC) and DE-NA0003856 (Laboratory for Laser Energetics, LLE). The Flash Center for Computational Science also acknowledges support from the U.S. DOE NNSA under Subcontracts 536203 and 630138 with LANL and B632670 with LLNL. The speaker acknowledges and thanks the Center for Integrated Research Computing (CIRC) at the University of Rochester, as well as the High Performance Computing Group of the Theory Division at the Laboratory for Laser Energetics, University of Rochester.

Bio: Marissa is a PhD Candidate in the Department of Physics and Astronomy at the University of Rochester with an upcoming defense. She has spearheaded the Z-pinch implementation and development in the FLASH Code since 2017, and has contributed to several magnetized plasma experimental campaigns through validated numerical modeling. Her research interests revolve around the concert of magnetohydrodynamics, turbulence, and how plasma properties impact the dynamics of its system when conducted in the spirit of verification and validation.

Title: Plasma Waves and the Compressibility of Warm Dense Hydrogen

Abstract: Collective oscillations in a plasma, much like phonons in a solid, can modify the internal energy and transport properties of a substance, but are difficult to simulate with today's ab initio techniques. For warm dense hydrogen, where the thermal and Fermi energies are both in the vicinity of 1 Ry = 13.6 eV, plasma waves offer a possible resolution to recently-reported compression differences between theoretical hydrogen models and shock experiments.

Bio: Ryan Rygg is the high-energy-density (HED) experiments group leader at the University of Rochester's Laboratory for Laser Energetics (LLE). He has been leading experiments at large HED facilities such as OMEGA and the National Ignition Facility for 20 years while at the Massachusetts Institute of Technology, Lawrence Livermore National Laboratory, and now LLE. His research includes development of novel experimental platforms for materials at HED conditions with applications in astrophysics, fundamental science, and inertial confinement fusion.

Title: Los Alamos National Laboratory: Mission Scope and Opportunities

Abstract: This talk will introduce the mission space of Los Alamos National Laboratory, and will focus primarily on introducing the type of work performed in the Weapons Physics Directorate. We will touch on career paths to and within the Laboratory, and will discuss the breadth of projects and challenges being worked on, as well as opportunities for students, postdocs, and early-career staff.

Bio: Leslie Sherrill has spent her career in the X Theoretical Design Division at Los Alamos National Laboratory, as a student, postdoctoral researcher, staff scientist, project leader, and now line manager. She is currently the Group Leader for the Integrated Design and Assessment Group, which contributes to sustaining the effectiveness of the current U.S. nuclear stockpile while also developing design and certification options for the future U.S. stockpile. Leslie completed her Ph.D. in Physics at the University of Nevada, Reno in 2006, under Professor Roberto Mancini. Her dissertation was focused on the spectroscopic characterization of Inertial Confinement Fusion (ICF) implosions. Leslie became a staff scientist in 2008, and was active early in her career in a range of projects centering around studying turbulent mix in high energy density physics experiments, which culminated in a successful multi-year experimental campaign to study reshock and shear-driven mix at the Laboratory for Laser Energetics’ OMEGA laser facility. Leslie is a 2011 graduate of the LANL Theoretical Institute for Thermonuclear and Nuclear Studies (TITANS) program. She has worked on and led a wide range of technical products associated with stockpile stewardship, verification and validation efforts, developing new capabilities in advanced simulations, and global security. In 2019, Leslie was named a 2020/2021 Fellow of the Oppenheimer Science and Energy Leadership Program (OSELP), which is a fellowship program for exceptional leaders from the Department of Energy’s National Laboratories.

Title: Achieving a Burning (and Igniting, by most definitions) Plasma on the National Ignition Facility (NIF) Laser*

Abstract: One of the scientific milestones in fusion research on the path to ignition is creating a burning plasma. A burning plasma occurs when the energy deposited by the fusion-produced alpha particles is the dominant source of heating of the plasma – this is a necessary step to reach ignition. Over the last year, experiments on the NIF laser have reached this state using two indirect-drive designs; these two designs use larger capsules than had been used previously while maintaining the other important parameters of implosion velocity, low-mode symmetry, late-time ablation pressure, and high Z mix. To drive larger capsules with the same amount of laser energy, the larger capsules had to be driven in a similar size hohlraum, which makes maintaining a symmetric drive more difficult, and required the use of additional techniques to mitigate low-mode asymmetry.

One of these designs, Hybrid E, has also achieved ignition by the Lawson criterion. Under that definition of ignition, the fusion-produced alpha heating dominates the power balance in the hotspot – overcoming radiative and conduction losses. The experiment on Aug 8, produced 1.35 MJ, which is a capsule gain (yield/capsule absorbed energy) of about 6x. The target gain, yield/laser energy, was 0.7 – which did not meet the NAS definition of ignition = gain 1. This design is likely on the ignition cliff, which means it is in a sensitive part of parameter space – repeat experiments to date have all achieved capsule gain > 1 but with lower yields than the August experiment.

Since the start of experiments on NIF, progress has been made in steps. At each step, a combination of experimental data (including improved diagnostics), theory, and modeling is used to identify and understand the limiters in performance. New designs are then developed using this understanding – this generally results in an increase in performance until the next limiter becomes dominant. This cycle has produced several physics milestones on the way to ignition. First was fuel gain, where the neutron yield exceeds the energy in the deuterium-tritium (DT) fuel [1]. Next was “alpha heating,” in which the neutron yield is doubled due to the additional energy deposited in the DT fuel by alpha particle stopping [2,3]. Now, we have achieved the burning plasma state [4]. In this talk, we will review these new designs and experiments and show how the August experiment compares with several published ignition metrics.

*Work performed under the auspices of the U. S. Department of Energy by LLNL under contract DE-AC52-07NA27344

Bio: Debbie came to the Lawrence Livermore National Lab as a graduate student in the U.C. Davis Department of Applied Science and received her PhD in 1993. Debbie’s technical expertise is in hohlraum physics and design. She has participated in experiments on the National Ignition Facility laser since they began in 2009 and her work played a role in the recent 1.35 MJ shot. Debbie became a Fellow of the American Physical Society (APS) in the Division of Plasma Physics in 2014 and was a co-recipient of the APS John Dawson Award for Excellence in Plasma Physics in 2012 for work on NIF. She was recently named the division leader for Design Physics Division at LLNL. When not working, she enjoys traveling and spending time with her daughter, her daughter’s fiancé, and her friends. During COVID, she started baking sourdough bread.

Title: Studying Matter at Extreme Conditions at Sandia National Laboratories

Abstract: High energy density matter spans an enormous range of temperatures and densities and can be produced by a variety of experimental drivers. Here, we survey a range of pulsed power experiments that produce plasmas with Mbar to Gbar pressures. This range of material conditions challenges atomic-scale models, which must incorporate thermal excitation, ionization, and non-equilibrium effects for hot and warm plasmas as well as pressure ionization, degeneracy, and strong coupling effects for dense plasmas. We describe an atomic-scale modeling effort based on a self-consistent-field model that generates constitutive data and direct observables. Finally, we survey research opportunities at the Pulsed Power Sciences Center at Sandia National Laboratories.

This work was supported by SNL's LDRD program, project number 218456. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

Bio: Stephanie Hansen is a Distinguished Member of the Technical Staff in the ICF target design group at Sandia National Laboratories, where she studies the atomic-scale behavior of atoms in extreme environments and develops atomic, spectroscopic, equation-of-state, and transport models to help predict and diagnose the behavior of high energy-density plasmas. She is the author and developer of the SCRAM non-LTE spectroscopic modeling code and MUZE, a self-consistent field code used for equation-of-state, scattering, and transport calculations. She received an Early Career grant from the Department of Energy’s Office of Fusion Energy Sciences in 2014, was awarded the Presidential Early Career Award for Scientists and Engineers in 2017, and was elected a Fellow of the American Physical Society’s Division of Plasma Physics in 2019. She holds degrees in Physics and Philosophy from the University of Nevada, Reno and has been a Visiting Associate Professor at Cornell University since 2012.

Title: Lawrence Livermore National Laboratory: Student, Postdoc and Faculty Research and Job Opportunities

Abstract: Our mission at Lawrence Livermore National Laboratory (LLNL) is to make the world a safer place. We apply science and technology to advance knowledge in basic and applied science. With expertise that spans world-class basic science to advanced technologies, we have always been at the forefront of the world’s most important scientific discoveries.

The goal of LLNL’s University Relations & Science Education Program (URSE) is to foster university collaborations that sustain long-term academic partnerships between Lab researchers and the academic community. We engage students, postdocs, and faculty in collaborative research and development. I will present an overview of some of the research areas we invest in, and conclude with a range of student, postdoc and faculty opportunities for engagement and collaboration.

Speaker Bio: Dr. Annie Kersting is the Director of University Relations and Science Education at Lawrence Livermore National Laboratory. She oversees a broad range of educational science and technology programs and initiatives that advance the mission and vision of the Laboratory, including the Lab’s postdoctoral program, student programs, institutes & centers, and our STEM education outreach program. She works with the Laboratory’s senior leadership to develop and execute strategies, build strategic partnerships with universities and foster collaborative research and education initiatives to ensure a workforce pipeline of top-tier science and technology talent.

Dr. Kersting is an environmental radiochemist with an active research group in environmental radiochemistry. Her current research is focused on identifying the dominant bio-geo-chemical processes and the underlying mechanisms that control contaminant cycling in the environment. She has co-authored over 60 publications and was awarded the ACS Garvan-Olin in 2016 award for outstanding research in chemistry, leadership and service.

She is also the Research Integrity Officer for LLNL.

Title: Innovation and Impact – Science at Lawrence Livermore National Laboratory

Abstract: Lawrence Livermore National Laboratory is a Department of Energy national laboratory dedicated to applying leading edge science and technology to address the most pressing challenges facing the nation and the world today, from pandemic disease to climate change to national security and beyond. This talk will explore the mission applications, science and technology foundations, and unique environment of LLNL and offer insight into building a career at the national labs.

Speaker Bio: Dr. Budil has a BS in physics from UIC (1987), and a PhD in engineering/applied science from UC Davis (1994).

For addition background, see:

Title: Particle-In-Cell Simulations of Stimulated Raman Scattering in Magnetic Fields

Abstract: Stimulated Raman scattering (SRS) has been an important topic throughout ICF history, but it is only relatively recently that the behavior of SRS in magnetic fields has been closely studied. SRS can be mitigated in ICF-relevant regimes by weak magnetic fields (wc/wp << 1) due to the damping of electron plasma waves (EPWs) propagating perpendicular to the magnetic fields. However, we have also found that magnetic fields can potentially enhance SRS activity by interfering with the nonlinear frequency shift of SRS-driven EPWs, thereby indirectly enhancing the frequency resonance between the light and plasma waves involved in SRS. Furthermore, in some parameter regimes, the SRS waves can themselves be unstable (e.g. the backscattered light wave can decay via rescatter and the backscattered EPW can decay via LDI), and for finite-width waves in multi-dimensions, the damping and transverse evolution of SRS EPWs depends sensitively on wave-particle interactions that can be impacted by magnetic fields. We show particle-in-cell simulations that illustrate how magnetic fields impact SRS and EPWs across a wide range of laser and plasma parameters.

Speaker Bio: Ben Winjum uses computer simulations to study the nonlinear behavior of plasma waves and laser-plasma interactions relevant to inertial fusion, specifically stimulated Raman scattering. He obtained his Ph.D. at UCLA in 2010 and currently works as a staff member in UCLA’s Institute for Digital Research and Education, where he works on advanced computing and data analytics projects in support of both research and education.

Title: Dynamic Failure in Laser Shock-loaded Iron

Abstract: The spall response of pure iron was studied using high power pulsed laser experiments at the LLNL Janus Laser Facility (JLF) and the Dynamic Compression Sector (DCS). Thin iron foils of varying initial microstructures were subjected to peak pressures of 40 – 60 GPa and strain rates ranging from 10^6 s^-1 – 10^7 s^-1. Simultaneous time-resolved free surface velocity measurements and recovery techniques at JLF were used to investigate spall strength and failure mechanisms. At DCS, simultaneous free surface velocity measurements and in-situ X-ray diffraction were used to investigate phase transitions during spall. These uniaxial strain experiments yielded strengths between 5 and 10 GPa for nanocrystalline and single crystal iron, respectively. Post-shock characterization and Molecular Dynamics simulations verify that this difference in strength is due to void initiation sites: grain boundaries in nano and polycrystalline iron and twin boundaries in single crystal iron. The complete α-ϵ phase transition during compression was observed, followed by a rapid transformation back to α-Fe. The grain structure during compression and release/spall failure is still being investigated.

Speaker Bio: In my research I investigate the behavior of iron under extreme pressure and strain rate conditions. I primarily use laser shock experiments to measure mechanical properties, supplemented with simulations. Iron strength under compression is studied using Rayleigh-Taylor instability growth to infer the yield strength in extreme regimes. Iron strength under tension is studied though spallation, a dynamic failure process. In both cases the effect of material microstructure and composition is investigated through pre- and post-shock material characterization.

Title: Magnetic Field Distribution of Z-pinches Driven by the CESZAR Linear Transformer Driver

Abstract: Gas-puff Z-pinches serve as powerful x-ray and neutron sources and have been studied in a number of configurations for their potential use in nuclear fusion. Understanding the Z-pinch process requires diagnosis of the evolution and behavior of the currents and magnetic fields which drive the implosion. Presented here are experimental results on the current distribution by measuring local magnetic field measurements using emission spectroscopy. The oxygen gas-puff experiments were performed on the 500-kA peak current, 180 ns rise time linear transformer driver (LTD) CESZAR. Azimuthal magnetic field measurements were made using ultraviolet emission from oxygen in a liner-on-target configuration, exploiting the polarization properties of the Zeeman effect. The fusion-relevant liner-on-target arrangement allowed for measurements of Bθ at the liner-target interface when oxygen was used as the inner target gas, resulting in values of Bθ of up to 4 T. Local measurements at the plasma-vacuum interface when oxygen was used as the shell liner resulted in measured values of Bθ ranging from 2 – 8 T. In addition to the magnetic field diagnostic, a multi-frame XUV pinhole camera was utilized, providing information of the implosion dynamics. Experimental results are compared with calculated values of Bθ and discrepancies are discussed. 

Speaker Bio: Nicholas Aybar is a PhD candidate at UC San Diego in Prof. Farhat Beg's Z-pinch group. He uses spectroscopy in pulsed power experiments to study high energy density plasmas, primarily by measuring magnetic fields to investigate physical processes in Z-pinch plasmas. He is a co-founder of the IEEE student branch chapter of Nuclear & Plasma Sciences Society (NPSS) at UCSD which promotes outreach and interest in nuclear and plasma research & technology.

Title: Z-Pinch Research at UC San Diego

Abstract: The Z-pinch is one of the most well-studied methods for high energy density plasma generation. Z-pinches have been used for a variety of applications such as thermonuclear fusion and as intense x-ray sources, among others. These applications are made possible due to the simplicity and flexibility in configurations of these devices, including gas puffs, wire arrays, fiber pinches, gas-embedded pinches, and dense plasma foci, among others [1,2]. The High Energy Density Physics Group at UC San Diego has an extensive experimental and modeling program in a variety of pulsed power Z-pinch devices. The focus in this presentation will be on i) gas puff Z-pinches, ii) X-pinches and iii) dense plasma focus work.

Gas puff Z-pinches are attractive x-ray and neutron sources [3]. We have carried out gas puff experiments on the newly-commissioned 1 MA linear transformer driver (LTD) CESZAR [4], which shows energy coupling to the load with an efficiency that is an order of magnitude greater than conventional Marx bank based generators [5]. These pinches are highly susceptible to the Magneto Rayleigh Taylor Instability (MRTI), which develops during the implosion and can disrupt the plasma column, preventing the achievement of conditions required for thermonuclear fusion and intense x-ray pulses. The MHD simulations predict that a combination of both external magnetic field and density tailoring can mitigate MRTI with reduced yield penalty [6].

Wire X-pinches (WXPs) have been studied comprehensively as fast (∼1 ns pulse width), small (∼1 μm) x-ray sources, created by twisting two or more fine wires into an “X” to produce a localized region of extreme magnetic pressure at the cross-point [7] Recently, two alternatives to the traditional WXP have arisen: the hybrid X-pinch (HXP) [8], composed of two conical electrodes bridged by a thin wire or capillary, and the laser-cut foil X-pinch (LCXP), cut from a thin foil using a laser. We have carried out experiments to compare copper wire, hybrid, and laser-cut foil X-pinches on a single experimental platform (∼200 kA, 150 ns rise time GenASIS driver). All configurations produced 1–2 ns pulse width, ≤5 μm soft x-ray (Cu L-shell, ∼1 keV) sources (resolutions diagnostically limited) with comparable fluxes. WXP results varied with linear mass and wire count, but consistently showed separate pinch and electron-beam-driven sources. LCXPs produced the brightest (∼1 MW), smallest (≤5 μm) Cu K-shell sources (~8 keV), and spectroscopic data showed both H-like Cu Kα lines indicative of source temperatures ≥2 keV, and cold Kα characteristic of electron beam generated sources [9].

The Dense Plasma Focus (DPF) is a long-studied Z-pinch variant. In a Mather-type DPF, the plasma is first accelerated axially and later implodes radially, with applications including neutron/fusion sources, soft x-ray sources, and ion beam sources [10]. Our work on DPFs has featured two devices: a 10 kJ, 300 kA, 2.5 μs risetime tabletop DPF at UCSD, and the 2 MJ, 2 MA, 6 μs risetime Gemini DPF at the Nevada Test Site. Experiments using the UCSD DPF demonstrated the significance of insulator conditioning on soft x-ray production in neon gas; machined insulator sleeves disrupt the azimuthal symmetry of the incipient plasma sheath and result in off-axis focusing, reduced hot-spot formation, and reduced x-ray yield [11]. Ongoing studies investigating the role of insulator length on neutron production using a deuterium fill have also revealed several interesting trends in optimal fill pressure as a function of insulator length. In the Gemini experiments, we investigated the effect of 0.01-1.0% Kr doping of deuterium on neutron production. MHD simulations revealed that the increased radiation due to the Kr results in a tighter pinch and affects both the thermonuclear neutron yield and pulse shape [12]. Experimentally, we found that the addition of 0.1% Kr is an optimized concentration at 2 MA, which placed in context of data from previous Kr-doped deuterium DPF experiments at lower currents interestingly suggests that the optimal concentration of Kr decreases with increasing driver current [13].

Speaker Bio: Farhat Beg is a Professor of Engineering Physics at the Department of Mechanical and Aerospace Engineering at the University of California, San Diego. He received his Ph.D. from Imperial College London. He joined University of California San Diego as a faculty in 2003. His expertise is in the field of inertial and magneto inertial fusion, laser plasma interaction, pulsed power driven X- and Z-pinches, and neutron sources. He has published over 240 papers in refereed journals, including Nature, Nature Physics, Nature Communications and Physical Review Letters, with total citations exceeding 9000 with and H-index of 49, according to the ISI Web of Knowledge. He is the fellow of the American Physical Society (APS), the Institute of Electrical and Electronics Engineers (IEEE) and the American Association for the Advancement of Science (AAAS). He been a winner of the Department of Junior Faculty Award (2005) and IEEE Early Career Award (2008). He has served twice as the Chair of the High-Energy Density Science Association (HEDSA) in 2009/2010 and in 2017/2018. The HEDSA is an association of scientists from academia that promote High-Energy Density Laboratory Plasma in universities and small businesses, as well as in national laboratories. He also served as the Chair of the National Ignition Facility User Group from 2017-2019. Dr. Beg served as the Director of CER from 2015 to 2019.

Title: Collisionless-Weibel Filamentation under Varying Plasma Conditions

Abstract: The ion-Weibel instability is a leading candidate mechanism for the formation of collisionless shocks observed in many astrophysical systems. Experimental and computational studies have shown that the ion-Weibel instability drives filamentary B-field structures in interpenetrating plasma flows with the capability to mediate collisionless shock formation and subsequent particle acceleration. Recent experimental results will be discussed that focused on studying the ion-Weibel instability under various plasma conditions through utilization of different ion species and experimental geometries. Filamentary B-field structures are observed under all conditions and characterized through Fourier analysis of processed proton images. Linear instability analysis is performed using benchmarked FLASH simulations to address the temporally varying plasma conditions and their effect on Weibel-filament evolution. Results from these analyses suggest that the initial plasma conditions tend to set the Weibel spectrum characteristics in counter-streaming plasma experiments.

Speaker Bio: Mario Manuel received his PhD in Applied Plasma Physics from MIT in 2013 for the observation and measurement of self-generated B-fields from that ablative Rayleigh-Taylor instability in high-energy-density (HED) systems. This work earned him the Marshall N. Rosenbluth Outstanding Doctoral Thesis Award from the APS Division of Plasma Physics in 2014. As a NASA Einstein Postdoctoral Fellow at the University of Michigan, Dr. Manuel's research interests turned to laboratory astrophysics and the study of magnetized jets. Dr. Manuel is now a research scientist at General Atomics, where he provides target-physics support to many researchers in inertial confinement fusion, laboratory astrophysics, and radiation source development. His direct research interests are in magnetized HED plasmas and the development of new technologies to foster rep-rated HED science.

Title: Extended MHD with FLASH: A Numerical Toolset for Magnetized Plasma Experiments

Abstract: In this talk I discuss the new capabilities of the FLASH code and its application to magnetized plasma experiments. FLASH is a publicly available, finite-volume Eulerian, spatially adaptive radiation magnetohydrodynamics (MHD) code developed by the Flash Center for Computational Science, which can treat a broad range of physical processes. FLASH performs well on a wide range of computer architectures and has a broad userbase spanning numerous research communities. Extensive high energy density physics (HEDP) capabilities exist in FLASH, making it a powerful open toolset for modeling magnetized plasma experiments. I summarize these capabilities and outline recent extended-MHD additions that significantly expand FLASH’s range of plasma applications, enabling the modeling of Z-pinch, fusion, and magnetized HEDP experiments. I showcase FLASH’s ability to simulate ab initio complex laboratory astrophysics experiments of magnetized plasmas, performed by the Turbulent Dynamo (TDYNO) collaboration. Finally, I describe several collaborations with the HEDP community in which FLASH simulations were used to design and interpret magnetized plasma experiments.

Speaker Bio: Dr. Petros Tzeferacos is the director of the Flash Center for Computational Science, an associate professor at the Department of Physics and Astronomy, and senior scientist at the Laboratory for Laser Energetics at the University of Rochester. He received his degree in Physics from the Physics Department of the University of Athens, Greece, in 2006, and earned his Ph.D. in Physics and Astrophysics from the Physics Department of the University of Turin, Italy, in 2010. His doctoral research was on jet-launching mechanisms in astrophysical accretion disks. From 2010-2012 he was a postdoc at the Department of Physics of the University of Turin, where he worked on accretion disk dynamics, numerical methods for computational astrophysics, and the development of the astrophysics code PLUTO. In 2012 he joined as a postdoc at the Department of Astronomy & Astrophysics of the University of Chicago, where he became research assistant professor in 2013 and research associate professor in 2019.

Tzeferacos has been responsible for the development of the FLASH code since 2013; FLASH is a publicly available multi-physics high-performance computing code used in plasma physics and astrophysics research. He became the associate director of the Flash Center in 2013 and its director in 2018. In 2020, Tzeferacos relocated the Flash Center for Computational Science to the University of Rochester. Tzeferacos works on plasma physics and astrophysics, combining MHD theory, numerical modeling, and laser-driven laboratory experiments, to study fundamental astrophysical plasma processes with a focus on magnetized turbulence, dynamo (2019 John Dawson Award from the APS-DPP), and charged particle acceleration. He was elected vice chair of the High Energy Density Science Association in 2017, member of the Omega Laser User Group Executive Committee in 2018, and vice chair of the NIF User Group Executive Committee in 2019.

Title: Pre-magnetized Triple Gas-puffs as a Magento-inertial Neutron Source

Abstract: The Z-pinch has a long history of diverse applications as an efficient neutron and X-ray source. This talk will place the gas-puff Z-pinch within that context, and it will discuss two fundamental challenges for the gas-puff Z-pinch as a neutron source: the magneto-Rayleigh-Taylor instability and thermal conduction losses. We predict with radiation-magnetohydrodynamic simulations that these challenges could be successfully addressed by using a triple-nozzle (two annular “liners” and an on-axis deuterium target) with a pre-embedded axial magnetic field using the nominal parameters for the CESZAR linear transformer driver (850 kA, 160 ns) [1], at which current level yields of order 108-109/cm are predicted. These simulations also predict material-dependent effects on pinch stability and target heating and compression, suggesting an optimal configuration is a high-Z outer liner and lower-Z inner liner. The talk concludes with a discussion of scaling the concept to hypothetical drivers with peak currents of up to 20 MA, at which current yields of order 1014/cm are predicted.

Speaker Bio: Jeff Narkis is a postdoctoral scholar at UC San Diego who conducts simulations using various codes as part of Prof. Beg’s Z-pinch group, where he received his PhD in 2019. His primary area of interest is in magneto-inertial fusion as a neutron source for commercial applications, inspired in part through his PhD research funded through ARPA-E’s ALPHA program. He chairs CMEC’s subcommittee on Diversity, Equity, Inclusion, and is proud to be part of a growing coalition of scientists and students that supports more aggressive implementation of DEI best practices within the plasma physics community. 

Title: Material Physics with Pulsed Power at Sandia

Abstract: The behavior of materials in extreme conditions is not only fascinating with many scientific challenges, a quantitative understanding is vital for our ability to model stars, planets, and nuclear weapons with high fidelity. At Sandia, we employ pulsed power technology and facilities like the Z-machine and THOR to investigate materials over a range of conditions from normal to High Energy Density (HED). In this presentation, I will describe how we utilize pulsed power to drive materials to high pressure without making them hot and present a broad range of recent work on equation of state, phase transitions, phase transition kinetics, and material strength for different materials.

Speaker Bio: After obtaining a Master of Science in Engineering Physics and realizing that there was so much more to explore in the study of physics, I continued on in graduate school modeling hydrogen diffusion using path-integral Monte Carlo. In particular, I investigated the transition from classical hopping diffusion to quantum tunneling for hydrogen on metal surfaces in Goran Wahnstrom's group at Chalmers University. Following graduate school, I was a postdoctoral scholar in Horia Metiu's group at University of Santa Barbara, California, modeling growth on metal surfaces, accelerating simulations by a multi-scale coarse-graining approach.

During 1999-2000, I returned to Sweden and first worked on defects in solids, in particular formation energies and diffusion barriers for vacancies at the Royal Institute of Technology in Stockholm. I then did research in telecommunications at Allgon Systems in Taby. My work on vacancies continued at Sandia National Laboratories, New Mexico. After a few years a colleague, Michael Desjarlais, introduced me to high energy-density physics as a very interesting area of research for density functional theory (DFT) and that's where my main focus has been since then.

Title: First-Principles Equation of State Database for Warm Dense Matter Computation

Abstract: We put together a first-principles equation of state (FPEOS) database for matter at extreme conditions by combining results from path integral Monte Carlo and density functional molecular dynamics simulations of eleven elements and ten compounds [1]. For all these materials, we provide the pressure and internal energy over a wide density-temperature range from 0.5 to 50 g/cc and from 105 to 109 K, which are based on 5000 first-principles simulations. Here we focus on isobars, adiabats and shock Hugoniot curves of different silicate in the regime of L and K shell ionization. We discuss the validify of the linear mixing approximation that we employ in our FPEOS database to study the properties of mixtures and compounds at high density and temperature. This talk concludes with discussing the phase diagram of magnesium oxide. The B1, B2, and liquid phases and anharmonic effects are analyzed [2]. 

Speaker Bio: Burkhard's research uses computer simulations to understand the interior and evolution of giant planets. Materials in planetary interiors are exposed to extreme temperature and pressure conditions that cannot yet be reached with laboratory experiments. Instead the group relies on highly accurate first-principles computer simulations techniques. With these methods, the group recently explained why neon is depleted in Jupiter's atmosphere and provided strong, though indirect evidence for helium rain to occur in giant planets. The group's recent simulations predict core erosion to occur in gas giant planets.