Past Seminars

Past Seminars

Organized Most Recent First

Wednesday, September 7

Arianna E Gleason-Holbrook | SLAC National Accelerator Laboratory, Staff Scientist

Abstract & Bio

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.

Wednesday, August 3 - Special Joint Seminar with CDAC!

Sebastien Hamel | Lawrence Livermore National Laboratory
(THIS TALK WAS NOT RECORDED DUE TO A PENDING PUBLICATION IN NATURE)

Abstract & Bio

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.

Wednesday, July 6, 2022

Marissa B. P. Adams | Flash Center for Computational Science, Department of Physics and Astronomy, University of Rochester


Abstract & Bio

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.

Wednesday, April 6, 2022 - Special Joint Seminar with CDAC!

Ryan Rygg | University of Rochester’s Laboratory for Laser Energetics, Senior Scientist in the Experimental High-Energy-Density Physics Group, and an Assistant Professor of Research in the Departments of Mechanical Engineering and Physics and Astronomy
(THIS TALK WAS NOT RECORDED)

Abstract & Bio

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.

Wednesday, March 2, 2022

Leslie Welser Sherrill | Los Alamos National Laboratory, Group Leader for the Integrated Design and Assessment Group
(THIS TALK WAS NOT RECORDED DUE TO LANL REQUIREMENTS)

Abstract & Bio

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.

Wednesday, February 2, 2022 - Special Joint Seminar with CDAC!

Debra Callahan | Lawrence Livermore National Laboratory, Division Leader for Design Physics Division

Abstract & Bio

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.

[1] O. A. Hurricane, et al., Nature 506, 343 (2014)
[2] S. Le Pape, et al., Phys. Rev. Lett. 120, 245003 (2018)
[3] D. T. Casey, et al., Phys. Plasmas 25, 056308 (2018)
[4] A. B. Zylstra, O. A. Hurricane, et al. accepted for publication

*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.

Wednesday, January 5, 2022

Stephanie Hansen | Sandia National Laboratories, Distinguished Scientist | Cornell University, Visiting Associate Professor

Abstract & Bio

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.

"Studying Matter at Extreme Conditions at Sandia National Laboratories"

2021 Seminars

Wednesday, December 1, 2021 - Special Joint Seminar with CDAC!

Annie B. Kersting | Lawrence Livermore National Laboratory | Director of University Relations and Science Education

Abstract & Bio

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.


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

Wednesday, November 3, 2021 - Special Joint Seminar with CDAC!

Kim Budil | Lawrence Livermore National Laboratory | Director

Abstract & Bio

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:

https://www.llnl.gov/kim-budilhttps://www.llnl.gov/news/national-ignition-facility-experiment-puts-researchers-threshold-fusion-ignitionhttp://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.541.5827&rep=rep1&type=pdfhttps://www.sciencedirect.com/science/article/pii/0030401887903932

"Innovation and Impact – Science at Lawrence Livermore National Laboratory"

Wednesday, November 3, 2021

Ben Winjum, UC Los Angeles | Computational & Data Science Research Specialist | Center Member

Abstract & Bio

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.

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

Wednesday, October 6, 2021 - Special Joint Seminar with CDAC!

Gaia Righi, UC San Diego | Graduate Student, Materials Science and Engineering | Center Member

Abstract & Bio

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.

"Dynamic Failure in Laser Shock-loaded Iron"

Wednesday, August 11, 2021

Nick Aybar, UC San Diego | Graduate Student, Center for Energy Research | Center Member

Abstract & Bio

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.

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

Wednesday, July 7, 2021

Farhat Beg, UC San Diego | Prof. of Mechanical and Aerospace Eng. & Center for Energy Research | Center Director

Abstract & Bio

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].

[1] D. Ryutov, M. Derzon, M. Matzen, Reviews of Modern Physics 72, 167 (2000).[2] M. Haines, Plasma Physics and Controlled Fusion 53, 093001 (2011).[3] J. Giuliani, R. Commisso, IEEE Transactions on Plasma Science 43, 2385 (2015).[4] F. Conti et al., Physical Review Accelerators and Beams 23, 090401 (2020).[5] F. Conti et al., Journal of Applied Physics (in press).[6] J. Narkis et al., Physical Review Letters (under review).[7] S. M. Zakharov et al., Sov. Tech. Phys. Lett. 13, 115–121 (1987)[8] T. A. Shelkovenko et al., Phys. Plasmas 23, 103303 (2016).[9] G. W. Collins et al., Journal of Applied Physics 129, 073301 (2021).[10] M. Krishnan, IEEE Transactions on Plasma Science 40, 3189 (2012).[11] D. Housley et al., Journal of Applied Physics 129, 223303 (2021).[12] J. Narkis et al., Physics of Plasmas 28, 022707 (2021).[13] E. N. Hahn et al., Journal of Applied Physics 128, 143302 (2020).

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.

"Z-Pinch Research at UC San Diego"

Wednesday, June 2, 2021

Mario Manuel, General Atomics | Scientist | Center Member

Abstract & Bio

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.

"Collisionless-Weibel Filamentation under Varying Plasma Conditions"

Wednesday, May 5, 2021

Petros Tzeferacos, University of Rochester | Assoc. Prof. of Physics and Astronomy & Senior Scientist at the LLE | Center Site Lead, Co-PI

Abstract & Bio

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.

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

Wednesday, April 7, 2021

Jeff Narkis, UC San Diego | Postdoctoral Scholar, Center for Energy Research | Center Member

Abstract & Bio

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.

[1] F. Conti et al., Phys. Rev. Accel. Beams 23, 090401 (2020).

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.

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

Wednesday, March 3, 2021 - Special Joint Seminar with CDAC!

Thomas Mattsson, Sandia National Laboratories | Manager, R&D Science and Engineering

Abstract & Bio

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.


"Material Physics with Pulsed Power at Sandia"

Wednesday, February 3, 2021

Burkhard Militzer, UC Berkeley | Prof. of Earth and Planetary Sciences | Center Site Lead, Co-PI

Abstract & Bio

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].

[1] B. Militzer, F. Gonzalez-Cataldo, S. Zhang, K. P. Driver, F. Soubiran, "First-principles equation of state database for warm dense matter computation", Phys. Rev. E 103 (2021) 013203. DOI: 10.1103/PhysRevE.103.013203 Link to FPEOS webpage.[2] F. Soubiran, B. Militzer, "Anharmonicity and Phase Diagram of Magnesium Oxide in the Megabar Regime", Phys. Rev. Lett. 125 (2020) 175701. DOI: 10.1103/PhysRevLett.125.175701.

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.


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