Seminars

Benjamin Jodar

CEA/DAM

"In high-energy-density physics, Warm Dense Matter (WDM) physics has been identified as a challenging research area due to its unique location in the density-temperature map at the junction of plasma, solid and liquid states. Many of the assumptions and approximations that have been successfully applied either in plasma physics or in condensed matter theory do not apply, making it difficult to develop a consistent model for WDM. Over the past decades, exploring this regime has become crucial for laboratory astrophysics or Inertial Confinement Fusion.

For these reasons, a pulsed-power facility has been recently developed at CEA DAM Île-de-France for studying the expanded part of WDM regime. It is based on the pulsed Joule heating technique, originally proposed by Korobenko et al. [1], for inducing a solid to plasma phase transition to metallic foils confined into a sapphire cell [2]. In this presentation, we report about recent experiments conducted on aluminum and copper to assess electrical conductivity and thermodynamic properties across a density range from solid-state value down to 1/8 of the initial density, with pressure reaching up to 12 GPa and temperature up to 10 eV. Experimental results are compared to DFT-MD simulations and various equation of state and conductivity models extracted from the literature. As a result, our experimental data appear to be able to improve significantly the modelling of EOS and electrical conductivity in expanded WDM regime."

Dan Dolan

Washington State University

While mechanical states created by dynamic compression are well characterized, the corresponding temperatures states are much less constrained.  Dedicated and usually difficult techniques are required to determine temperature on nanosecond time scales.  This presentation describes fundamental challenges in any dynamic temperature measurement.  Specific emphasis is placed on optical pyrometry, linking the temperature of a sample to the visible/infrared light it emits.  This seemingly simple concept is prone to host of problems, but significant progress has been made.  Recent successes include low reflectance metals and water undergoing dynamic solidification.

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Hiroshi Sawada

University of Reno

High-intensity, short-pulse lasers enable the generation of energetic charged particles that can isochoric ally heat matter to extreme conditions relevant to laboratory astrophysics, materials science, and fast ignition for inertial fusion energy. While the properties of laser-driven charged particle beams are well understood, diagnosing the fast transient conditions they produce in solid and high-density targets remain challenging due to limited diagnostic capabilities with sufficient temporal and spatial resolutions. We present femtosecond and micron-scale resolved measurements of solid-density copper foils heated by laser-driven relativistic electrons, using an X-ray Free Electron Laser (XFEL). At the SACLA XFEL facility, relativistic-intensity thin copper foils irradiated by a relativistic-intensity femtosecond laser were probed with a 10-fs collimated XFEL pulse for two-dimensional X-ray imaging. Time-resolved images captured the electron-driven heat front propagating at approximately one-quarter the speed of light. By tuning the X-ray photon energy across the Cu K-edge, transmission changes were observed and used to infer electron temperatures and ionization states in the heated region, with support from two-dimensional particle-in-cell simulations. Our results reveal the formation of a highly ionized, hot plasma near the laser interaction region, surrounded by a Fermi-degenerate warm dense matter. These findings provide new insights into fast electron heating dynamics and demonstrate a powerful diagnostic for studying warm dense matter relevant to high-energy-density physics and fast ignition. Details of the experimental results and broader applicability will be discussed.

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Francesca Miozzi

Carnegie Institution of Science

Understanding the physicochemical properties of minerals and their relations under high pressure and high temperature conditions is fundamental to model and interpret observational data coming from planets inside and outside the solar system. The presence of different mineralogical phases can produce different interior structures which reflect in the model used to interpret exoplanet's mass -radius plots. Similarly, changes in the phases composing planetary cores can reflect in the planet's moment of inertia and global scale properties such as magnetic fields. In this presentation I will show how the range of information accessible with experiments can help unveiling these mineralogical properties and how they can be applied to the interpretation of current (or future) observational data.

Bethany Hopp

Los Alamos National Laboratory

The Earth and other terrestrial planets experienced one to several giant impacts during accretion and growth. Dynamic simulations of planetary impacts rely on equations of state that define the properties of materials under extreme pressure and temperature conditions. Recent experiments on forsterite, the Mg-endmember of the olivine mineral series, have shown that traditional analytical equation of state models have largely over-estimated the shock temperatures of this material, requiring a reformulation of the heat capacity to match the data. Here, we present shock compressibility and temperature measurements on the most abundant mineral compositions in Earth’s upper mantle, including olivine (Mg,Fe₂SiO₄) and bronzite (Fe-bearing pyroxene, (Mg,Fe)SiO₃) to above 1.5 TPa. By comparing the Fe-bearing compositions to Fe-free compositions over the same shock conditions, we see a distinct change in behavior above ~1 TPa when Fe is present in the mineral. We also present shock compression and temperature measurements on a bulk silicate Earth (pyrolite) glass composition, analogous to a magma ocean. Our experimental data are then combined to create a general analytical equation of state for silicates for use in planetary impact models.

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Lorin Benedict

Lawrence Livermore National Laboratory

I will describe our initial work towards the construction of a variable-composition EOS model for Fe/Ni mixtures, aimed for eventual use in the study of planetary interiors. First, our recently released pure-Fe and pure-Ni EOS models will be discussed, and then I will outline our scheme for creating from them free energy models for the 2-component mixture. I will emphasize the additional constraints (e.g., from various atomistic calculations) that we are using to quantify the details of the mixture thermodynamics for this system, as well as an intellectual conundrum that arises when attempting to construct multiphase mixture EOS models from multiphase EOSs for the individual components.

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Alex Pettitt

Cal State Sacramento

Spiral galaxies, like our Milky Way, are some of the most striking objects in astronomy. Modern observational efforts have unveiled a wealth of detailed information concerning their gaseous and stellar components, providing unprecedented insights into their properties, such as internal dynamics and star-forming potential. However, understanding what drives their structure and evolution is extremely difficult due to their highly complex nature. Numerical simulations allow us a unique tool to study them in great detail and to better guide models of how real galaxies behave. In this talk I will present numerical work by myself and my students that investigates how a galaxy’s structure impacts its properties, including what kind of physical processes determine whether a given galaxy is a good “star formation engine”. Of particular interest are the distinct morphological components of a given galaxy, such as spiral arms and bars, with many standing issues concerning the exact role they play.

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Steve Jacobsen

Northwestern University

Extreme conditions of pressure, temperature, radiation, etc. are found throughout the solar system. The study of Earth and planetary materials in extreme environments can address big questions about the formation of the Earth-moon system, while training the next generation of NNSA scientists. New shock-ramp experiments performed using pulsed power on the Z machine are testing a hypothesis that iron enrichment in dense oxides could account for ultra-low velocity zones atop the Earth’s core-mantle boundary. I will also feature recent SSAA-supported work from my group employing extreme environments to change the energy landscape in proteins and molecular machines, along with powder bed fusion of lunar regolith for off world construction applications.

Martin Richardson

University of Central Florida

The attributes of high energy lasers that are suitable for defense applications of directed energy are similar to those that are, or will be, required in many advanced technologies of the future. This review of the activities of the CDE@UCF will cover some new lasers and some novel pulsed and cw laser modalities that are used to investigate several non-linear propagation phenomena in the atmosphere and novel laser-plasma interactions. The talk will also cover the challenges of propagating high-power lasers in complex atmospheric environments, the sustainability of optical components and supply chain issues including ensuring a multiskilled workforce.

Claire Zurkowski

Lawrence Livermore National Laboratory

The toroidal diamond-anvil cell (tDAC) can routinely achieve pressures under static compression above 300 GPa, pressures relevant to the center of Earth and the deep interiors of multi-Earth mass exoplanets. Building intricate sample environments for high-quality equations of state (EoS), phase relations, and melting studies of planetary and other condensed-matter materials remains difficult in the tDAC. The small tDAC sample chamber (~4 – 6 µm diameter) presents a great challenge for embedding micron-sized samples in soft media for measuring the room-temperature EoS and in insulating media for exploring high-temperature properties. Here we will discuss our recent advancements in microfabricating a tDAC sample environment where we test high-strength Mo fully encapsulated in a copper medium. We demonstrate that compressing samples in a softer metal in the tDAC improves the compression environment and results in measured sample volumes comparable to those collected in noble-gas media at multi-megabar conditions. To target high-temperature studies, we further develop a large-volume toroidal design capable of reaching pressures >4 Mbar while accommodating a sample compartment as large as a typical laser-heating spot size (~30 um). This larger-volume configuration also offers ample space to insulate the sample under high temperature conditions. The tDAC sample packages developed through this work expand capabilities to obtain high-quality pressure-volume-temperature data for planetary and other condensed matter studies at multi-megabar conditions.

Do-Kyeong Ko

Advanced Photonics Research Institute, Gwangju Institute of Science and Technology (GIST), The Department of Physics and Photon Science, Republic of Korea

Since its establishment in 2001, the Advanced Photonics Research Institute (APRI), a research institute under the Gwangju Institute of Science and Technology (GIST), has made remarkable achievements in the development of ultra-high-intensity lasers and high-field science research. APRI has a 4.2 PW ultrafast laser research facility, which has achieved a record-breaking laser intensity of over 1023 Wcm-2, and has conducted many relativistic laser-matter interaction studies with this laser system. This presentation will provide an overview of APRI and introduce recent research activities and achievements at APRI in the areas of high-field science, including acceleration of high-energy particles (electrons, protons, ions), generation of high-energy photons (X-rays, gamma-rays), and all-optical nonlinear Compton scattering.

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Paul Yang

Flatiron Institute

Quantum Monte Carlo (QMC) methods have been useful in providing benchmark quality equation-of-state data for highly compressed matter such as dense hydrogen. The method’s ability to accurately capture strong electron correlations makes it more reliable than commonly used density functional theory approximations. Despite its high accuracy, the wide-spread adoption of QMC methods has been hindered by two main challenges. The first is a lack of a reliable source of trial wavefunction, which limits the accuracy and predictive power of practical QMC calculations. The second is a high computational cost, which constrains molecular dynamics and path integral simulations using QMC forces to small system sizes. In this talk, I will discuss recent works aimed at overcoming these challenges with the help of machine learning tools. Firstly, a neural quantum state (NQS), a neural-network representation of the many-body electronic wavefunction, has been shown to be flexible and accurate enough to capture the Fermi liquid to Wigner crystal transition in the two-dimensional electron gas [1]. Not only did these calculations achieve state-of-the-art accuracy, but they revealed unexpected short-range nematic spin correlations in the liquid prior to crystallization, suggesting the existence of an intermediate phase between the liquid and the crystal. Secondly, machine learned interatomic potentials (MLIPs) have been trained on QMC forces to enable large-scale path integral simulations of dense hydrogen [2]. The melting temperature of molecular hydrogen was found to depend sensitively on the accuracy of the underlying electronic structure approximation. The most accurate simulations predict much higher melting temperatures than previous estimates, reaching around 1500 K at 150 GPa. The updated melting line creates new questions about the existence of a melting temperature maximum and the fate of the molecular-to-atomic transition [3]. 

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Jane Pratt

Lawrence Livermore National Laboratory

The plasma that makes up the interior of stars spans many orders of magnitude in temperature, pressure, and density. These extreme changes define the multi-scale nature of fluid mixing mechanisms in the stellar interior that are responsible for the radial transport of chemicals. In this talk, I will discuss convection, the highly compressible physics surrounding the convective boundary, and the excitation of internal gravity waves. The study of these fluid eBects contributes to the 321D link, the eBort to improve 1D stellar structure and evolution models through 2D and 3D hydrodynamic simulations. This discussion will be supported by results from realistic global simulations of pre-main-sequence, main sequence, red giant, and Cepheid variable stars produced over the last ten years with the Multidimensional Stellar Implicit Code (MUSIC). I will then describe our new eBorts to use the next-generate, higher-order ALE code Marbl to produce simulations of variable stars and rapid rotators.  This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNLABS-871426

Bruce Remington

National Ignition Facility, Lawrence Livermore National Laboratory

Highlights from research done on the National Ignition Facility (NIF) laser through the Discovery Science program will be presented. Plasma nuclear reactions relevant to stellar nucleosynthesis and nuclear reactions in high energy astrophysical scenarios are being studied. [1] Equations of state (EOS) at very high pressures (0.1-100 TPa or 1-1000 Mbar) relevant to planetary cores, brown dwarf interiors, and white dwarf envelopes are being measured on NIF, and show that the level of ionization can significantly affect the compressibility of the sample. [2-6] Studies of Rayleigh-Taylor instabilities in planar and cylindrical geometries at high Reynolds number, relevant to supernovae explosions and ICF implosions, are being investigated. [7-12] Relativistically hot plasmas [13,14] and target-normal sheath acceleration (TNSA) of protons [15-17] are also being studied on the NIF ARC laser. Experiments to study magnetic reconnection at high energy densities are underway. [18] High velocity, low density interpenetrating plasmas that generate collisionless astrophysical shocks, magnetic fields, bursts of neutrons, and that accelerate particles relevant to cosmic ray generation are also being studied on NIF. [19-21] And NIF experiments have demonstrated strong suppression of heat conduction in a laboratory replica of galaxy-cluster turbulent plasmas. [22] A selection from these results will be presented and a path forward suggested.

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Mingsheng Wei

Laboratory for Laser Energetics, University of Rochester

The Omega Laser Facility at the University of Rochester’s Laboratory for Laser Energetics is one of the premier high-energy-density (HED) facilities funded by the National Nuclear Security Administration (NNSA). It comprises the 60-beam, 30-kJ OMEGA Laser System and the four-beam high-energy, high-intensity OMEGA EP Laser System. The two lasers share over 100 diagnostics and perform approximately 2000 highly diagnosed experiments annually. The Facility is primarily used to support NNSA’s Inertial Confinement Fusion Program. About one-third of the experimental time is provided to general user programs for basic research via the National Laser Users’ Facility and Laboratory Basic Science Programs with additional shot time on OMEGA EP through LaserNetUS (supported by the Department of Energy’s Office of Fusion Energy Sciences). The user programs currently support the education and training of 80 graduate students from over 20 universities. I will provide an overview of the basic science user programs and highlight user research in broad HED areas including laboratory astrophysics, high-pressure materials relevant to planets and exoplanets, magnetized HED plasmas, equations of state, warm dense matter, relativistic laser–plasma interaction and intense beam physics, nuclear physics, and inertial fusion energy. This material is based upon work supported by the Department of Energy [National Nuclear Security Administration] University of Rochester “National Inertial Confinement Fusion Program” under Award Number(s) DE-NA0004144 and by the Office of Science under Award Number DE-SC0024415 (LaserNetUS).

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Michael Bonitz

Kiel University

Recent decades have seen tremendous progress in experimental developments to produce and diagnose WDM. At the same time, the accuracy of measurements is necessarily finite, and often models are invoked to interpret the results. On the other hand, there has been an explosion of computer simulations of WDM that often successfully reproduce experimental results (including erroneous ones). So, how accurate are the simulations? In a recent review article [1] 27 experts have addressed the above questions for the (comparatively) simple, yet important example of dense hydrogen. I will present an overview which includes novel results for the thermodynamic properties, conductivity, and ionization potential depression. I will conclude with an outline about how accurate and predictive simulations can be achieved. [1] M. Bonitz et al., Towards first principles-based simulations of dense hydrogen, Phys. Plasmas in press (feature article), arxiv:2405.10627.

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Frank Graziani

High Energy Density Science Center, Lawrence Livermore National Laboratory

In 2025, the High Energy Density Science Center (HEDSC) will be celebrating its 10th anniversary. The HEDSC was established in late 2015 through a joint agreement between the Physical and Life Sciences, Strategic Deterrence (then Weapons and Complex Integration), and NIF and Photon Science directorates. The Center’s goal is to help build a high energy density science community through support of, and collaboration with, academic partners and to integrate those efforts with the programs at LLNL. The Center is built around four focus areas: (1) education, (2) outreach through workshops and seminars, (3) workforce pipeline to the programs, and (4) enabling research collaborations between LLNL and academic partners. In this talk, we will present the year FY24 in review and look at what lies ahead in FY25. Highlights of FY24 include a 10-week course offering in collaboration with UCSD in high energy density diagnostics, the hiring of a new HEDSC Fellow, support for workshops such as “Current Challenges in the Physics of White Dwarf Stars”,  a vibrant seminar series and summer student program, a sabbatical visit by Professor Ivan Oleynik of the University of South Florida, welcoming an IFE workforce coordinator, facilitating international engagements in HEDS with Japan and Israel, and our continued involvement in the Consortium for High Energy Density Science  funded by the NNSA Minority Serving Partnership Program. In FY25, we look forward to developing a new 10-week course on warm dense matter physics, a new 5-year strategic plan, welcoming Martin Richardson as our joint NIF-HEDSC sabbatical visitor, working with the University of California Livermore Collaboration Center on hosting workshops and a summer school, and much more.

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Felicie Albert

Jupiter Laser Facility, Lawrence Livermore National Laboratory

The Jupiter Laser Facility (JLF) at Lawrence Livermore National Laboratory (LLNL) is a mid-scale, kilojoule-class laser facility enabling experiments in laser, optical and high energy density science. This HEDS center seminar will present an overview of the JLF history, capabilities, impact on academic and programmatic research, as well as its role within LaserNetUS. The facility has just completed a 4-year long refurbishment and is welcoming users back through the LaserNetUS network. In addition to scientific discovery, JLF has historically served as a steppingstone to larger experiments at the NIF and OMEGA lasers.  JLF supports multiple laser platforms: Titan, Janus TA1, and COMET. Titan’s two-beam system is composed of a nanosecond, kilojoule long-pulse beam and a short- pulse beam with 1 to 10 ps pulses and energies up to 300 J, depending on pulse duration, and these beams can be used together or independently. JLF’s Janus system has two independent beams, each of which can produce 1 kJ at 1.053 μm with pulse lengths from 1 to 20 ns. The system fires approximately every 30 minutes and offers frequency doubling, as well as a variety of pulse shapes. COMET’s flexible configuration, which was designed primarily to generate laboratory x-rays, offers uncompressed pulse lengths from 500 ps to 6 ns, compressed pulses down to 0.5 ps, and beam energies up to 10 J.

Ben Idini

University of California, Santa Cruz

The search for habitable environments is at minimum a quest for unraveling the trails of water. In the early solar system, the formation of Jupiter may have played a key role in the delivery of water into an otherwise dry inner solar system. In this talk, I will present recent advances in planet formation and deep interior structure of the giant planets Jupiter and Saturn from observations obtained by NASA missions Juno and Cassini. I will put particular emphasis in our current challenges in determining Jupiter’s core extension due to uncertainties in the equation of state of the H-He system in the partially ionized regime. I will discuss how future experiments and computer simulations of the H-He system could help us unravel key mysteries of planet formation and the origin of water in our own planet Earth. 

Matt Caplan

Illinois State University

Abstract: Strongly coupled plasmas have Coulomb energies orders of magnitude greater than thermal energies and can be found in systems spanning electrically charged dusts to the cores of white dwarfs. As such, many of the physically relevant temperatures and densities are inaccessible to laboratory experiments on earth - but computation does not have these restrictions. I will present recent results of molecular dynamics simulations used to determine transport coefficients of strongly coupled plasmas, including plasmas at such high densities that they have crystallized.  

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Lucas Stanek

Sandia National Laboratory

Reliable simulations of high-energy-density plasma systems, such as inertial confinement fusion targets, require accurate descriptions of constitutive material properties such as equations of state, opacities, and transport coefficients. Usually, these properties are pre-computed using microscale models with varying levels of accuracy across a wide range of conditions and tabulated into datasets. The influence of uncertainties in these datasets on simulation output is application-dependent and largely unknown.  In this presentation, we describe state-of-the-art computations of conductivity and viscosity and present an efficient approach for generating families of tables with physics-informed uncertainties.  First, we present a summary of the recent Charged-Particle Transport Coefficient Code Comparison Workshop, which revealed significant variations in the values of transport coefficients computed by multiple approaches. We discuss some of these approaches and demonstrate an approach to generating ionic transport coefficients of plasmas that reduces the computational cost by orders of magnitude: from weeks to minutes. Next, we present an automated framework for generating tables useful for simulations: the framework couples a parameterized conductivity model, reference data, and Bayesian inference to generate an ensemble of datasets suitable for uncertainty quantification. Finally, we illustrate how this framework can be used in large-scale integrated magnetohydrodynamic simulations of inertial confinement fusion experiments underway on the Z Machine of Sandia National Laboratories.  This work was supported by SNL’s LDRD program, project numbers 230332 and 229428. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525; SAND2024-09336A.

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Ivan Oleynik

University of South Florida

The behavior of carbon under extreme pressures and temperatures is crucial for understanding the interiors of carbon-rich exoplanets and harnessing diamond ablators for inertial confinement fusion. The advent of powerful laser and pulsed-power compressions, in-situ X-ray synchrotron and free electron laser (XFEL) diffraction characterization, and exascale supercomputers opens up a new era of exploration of materials at extremes at an unprecedented level of detail. In this talk, I will discuss the transformative advances in the investigation of dynamically compressed carbon enabled by quantum-accurate, billion-atom molecular dynamics shock simulations on the DOE exascale supercomputer Frontier. By employing the most powerful computer in the world, we are able to simulate the atomic-scale dynamics of material responses at experimental time (nanosecond) and length (micrometer) scales. This includes the synthesis of the long-sought BC8 high-pressure post-diamond phase of carbon, the shock response of nanocrystalline diamond, and phase transitions in shocked amorphous carbon. These groundbreaking simulations guide our experimental campaigns at NIF, Omega, and EuXFEL facilities towards observing the predicted phenomena.

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Stefano Racioppi

University of Buffalo

Experimentally obtained X-ray diffraction (XRD) patterns can be challenging to interpret, hindering the full characterization of materials, pharmaceuticals, and geological compounds. In this talk, I will introduce a method based on a multi-objective evolutionary search that utilizes both a structure’s enthalpy and its similarity to a reference XRD pattern (comprised of a list of peak positions and their intensities) to streamline the structure solution of inorganic systems. By computing the similarity index for locally optimized cells that are then distorted to find the best match with the reference, this process overcomes both computational (e.g., choice of theoretical method and 0 K approximation) and experimental (e.g., external stimuli and metastability) limitations. I will demonstrate the efficacy of this methodology in uncovering complex crystal structures through a range of test cases, including inorganic minerals, pure elements subjected to extreme conditions, and molecular crystals. Our results show that this approach not only enhances the accuracy of structure prediction but also significantly reduces the time required to achieve reliable solutions, offering a powerful tool for advancing materials science and related fields. 

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Lance Labun

Tau Systems

Taking advantage of GV/cm acceleration gradients, laser-plasma accelerators appear poised to reduce the cost and footprint of high-energy particle beam facilities for a wide variety of applications.  Combining cutting-edge laser technology with centimeter-scale gas cells can, in a few hundred square meters of floor space, yield 8-10 GeV electron bunches with charge density comparable to that obtained from radio-frequency accelerators.  Laser Wakefield accelerator beams have a few unique advantages, such as naturally short (<30 fs) bunches, and the ability to produce secondary particles, such as photons and neutrons that naturally inherit the short pulse duration.  Tuning the laser and plasma enables the same machine to produce either higher-charge/lower-energy bunches or lower-charge/higher-energy bunches.  Tau Systems is a start-up headquartered in Austin, Texas, that is commercializing the laser Wakefield accelerator for several industrial applications.  I will describe some of Tau's activities and interests, highlighting progress on Wakefield-driven free-electron laser experiments at BELLA, electronics testing prototype experiments at UT, proposed laser-driven neutron and photon sources, and simulation and data analysis development.

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Alina Kononov

Sandia National Laboratory

Hydrodynamic simulations used to design and interpret fusion experiments rely on tabulated material properties over a wide range of pressures and temperatures as the target evolves from ambient conditions to a burning plasma. The intermediate warm dense regime presents unique challenges because models struggle to capture coexisting thermal and quantum effects accurately, while experimental characterization is rare and often suffers from large uncertainties. Here, we review ongoing work to advance computational methods for predicting electronic response properties of warm dense matter, including stopping power, x-ray scattering spectra, and optical conductivity. Using real-time time-dependent density functional theory (TDDFT), we benchmark and constrain efficient treatments based on average-atom methods and model dielectric functions. Since the credibility of these more approximate models then depends on the reliability of the first-principles data, we scrutinize the methodological choices of the TDDFT calculations and show that sensitivities to pseudopotential details, projectile trajectory, and finite-size effects can lead to significant errors in computed stopping powers of around 15%. We also discuss collective, nonlinear, and subtle band structure effects that are predicted by TDDFT, carry important implications for accurately simulating and diagnosing warm dense matter, and remain difficult for simplified models to capture. Finally, we consider the prospects of emerging quantum computing technologies enabling even more precise benchmark calculations. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

Geun Woo Lee

Korea Research Institute of Standards and Science/University of Science and Technology, Republic of Korea

Abundant H₂O phases form due to various configurations of hydrogen-bonded networks under wide ranges of temperature and pressure. In particular, at low temperature, the slow kinetics of the cooperative motion of H₂O molecules in the hydrogen-bonded networks can increase the chances that an ice phase takes place at deep metastable states across its equilibrium phase boundaries with high density and high bonding energy. Circumstantially, the most effective way to reduce the total Gibbs free energy of the ice is to create metastable phases which have slightly less energy than the ice. This process produces complicated transition pathways. Therefore, finding metastable ice phases are of importance to understand the phase transition mechanism.

However, such metastable phase formations and complicated transition pathways have been rarely observed at near and above room temperature, where thermodynamics is dominated for the phase transitions. Nevertheless, recent studies have raised the possibility to find metastable phases at room or high temperature, when deep metastability (or large driving force) can be achieved. Such examples are metastable ice VII in the stable regime of ice VI, high-density amorphous (HDA) at room temperature, and plastic ice VII at high temperature. In this regard, the ice crystallization due to the high degree of metastability and fast transition kinetics is a very interesting subject at high temperature and pressure conditions. By the aid of dynamic diamond anvil cell and XFEL techniques, we will discuss a new discovery of a metastable phase at room temperature which exists in the stable ice VI phase regime and report the hidden multiple crystallization pathways of H₂O via the new metastable ice phase and metastable ice VII phase.

Michael Wadas

California Institute of Technology

The mixing induced by a shock wave passing through a fluid interface can stimulate the ejection of high-velocity projectiles of one fluid into the other, which severely disrupt implosion symmetry in inertial confinement fusion (ICF) and transport stellar core elements during supernovae. Recent improvements in experimental diagnostics and numerical simulations reveal that such projectiles share key characteristics with classical fluid vortex rings, thus enabling a path to understand their dynamics. Our objective is to isolate the ejection of vortex rings from shocked interfaces and determine their scaling through numerical simulations and physical experiments. We find that the strength of the rings expectedly scales with the intensity of density and pressure gradients but saturates beyond a critical protrusion size, enabling an a priori prediction of the energy transported by vortex rings in ICF and supernovae.  Vortex dynamics may have also shaped the environment surrounding the progenitor of Supernova 1987A, which consists of evenly spaced gaseous clumps immersed in an equatorial ring. Our analysis suggests that the ring could have formed an unstable vortex dipole after acquiring vorticity from the progenitor wind, with a dominant wavenumber remarkably consistent with the number of observed clumps. Recent observations by the James Webb Space Telescope further confirm the plausibility that the present vortex instability mechanism induced clump formation.

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Krista Soderlund

University of Texas

Planetary magnetic fields exhibit remarkable variations that reveal clues to their deep interiors and internal histories. The Voyager 2 flybys, nearly 40 years ago, discovered that Uranus and Neptune have multipolar (i.e., non-dipole dominated) surface magnetic fields with comparable intensities, no clear symmetries along any axis, and unknown temporal variations. In contrast, Saturn and Mercury have strikingly axisymmetric fields and slow secular variation, while Jupiter and Earth have axial-dipole-dominated fields and more rapid secular variation. These observations lead to fundamental questions about what processes control the morphology, intensity, and temporal evolution of planetary magnetic fields. Despite general consensus that Uranus' and Neptune's magnetic fields arise from convection of electrically conducting fluids in their interiors, the mechanisms behind their asymmetric nature remain elusive. To address this gap, we present new results from numerical dynamo models integrating a background density profile that encompasses both interior and deep atmospheric layers, thereby incorporating critical coupling effects between these regions and consistently producing multipolar magnetic fields. Looking ahead, I will conclude by proposing future directions for missions, modelling, experiments, and theory necessary to answer outstanding questions about the dynamos of giant planets, both within our solar system and beyond.

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Dominik Kraus

Helmholtz-Zentrum Dresden Rossendorf

The interiors of planets and stars exhibit extreme conditions: High temperatures and enormous pressures create environments which are not fully understood and hard to encompass for state-of-the-art physics models. Applying the largest and most brilliant laser light sources, it is now possible to investigate such conditions in the laboratory. Recent efforts provide seminal insights into chemistry and phase transitions occurring deep inside giant planets and elucidate the electronic structure of elements in the interiors of brown dwarfs and stars. At the same time, highly interesting new materials may be formed via these conditions. Finally, creating stellar interior states in the laboratory may also allow to harvest nuclear fusion, the energy source of the stars, on Earth. I will present a showcase of recent experiments investigating these topics and provide an outlook for future developments, including prospects of the ambitious program "Fusion 2040" initiated very recently by the German government and its potential impact on high energy density science activities in Germany.

Sébastien Thevenin

CEA/DAM
University Paris-Saclay

In this work, we consider the problem of inferring the initial conditions of a Rayleigh-Taylor mixing zone by measuring the 0D turbulent quantities at an undetermined time. To this aim, we generate a large dataset of direct numerical simulations (DNS) within the framework of small-density contrast miscible fluids and where the initial interface deformations are determined by an annular spectrum parameterized by four non-dimensional numbers. In order to study the sensitivity of 0D turbulent quantities to the initial interface perturbation distributions, we build a surrogate model for the simulations using a physics-informed neural network (PINN). This allows to compute the Sobol indices for the turbulent quantities, disentangling the effects of the initial parameters during the mixing layer growth. Within a Bayesian framework, we use a Markov chain Monte-Carlo method to determine the posterior distributions of initial conditions given various state variables. This sheds light on the inertial or diffusive trajectories along with how the initial conditions are progressively forgotten during transition to turbulence. Besides, it selects which turbulent quantities are more suitable to predict the dynamics of Rayleigh-Taylor mixing zones as keeping better the memory of the flow. By inferring the initial conditions and forward propagating its maximum a posteriori (MAP), we then propose a strategy to model the Rayleigh-Taylor transition to turbulence.

Graeme Sutcliffe

Lawrence Livermore National Laboratory

The Biermann battery is thought to be the mechanism which generates the seed magnetic field in interstellar plasmas after which turbulent dynamo must be invoked to explain how seed fields (~10-20 G) are amplified up to the observed levels (~10-6 G). The Weibel instability is another candidate for the generation of seed fields: PIC simulations suggest that Weibel-generated fields might scale much more favorably for the long astrophysical length scales (𝐵∝𝐿0) than the Biermann-generated fields (𝐵∝𝐿-1). This possibility, however, requires a mechanism to explain how the Weibel fields might grow to larger length scales. Existing theory and simulations describing various details of Weibel filament mergers provide models that can be compared to data: a model agnostic to the magnetic-reconnection microphysics suggests that the long-term evolution of filaments progresses like 𝜆∝𝑡2, while a model invoking magnetic reconnection as the limiting factor in filament mergers suggests that filament wavelengths should follow 𝜆∝𝑡1/2. Distinguishing these models requires linearly saturated ion Weibel filaments, which were demonstrated in an array of prior experiments at OMEGA. One previous study made time-resolved measurements of CH-interpenetrating ion Weibel filaments and found a reasonable fit to the model but did not cover later times where the largest difference between models exists. The experimental campaign described in this talk seeks to investigate this question by pushing measurements to later times and testing the dependence of the merger rate on Lundquist number to see if magnetic reconnection is indeed the limiting physical mechanism in nonlinear Weibel filament evolution.

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Steeve Greaux

Ehime University Geodynamics Research Center

Laboratory studies of the elastic wave velocities in minerals under high pressure play a major role in enabling scientists to interpret seismic observations in term of composition and structure of the Earth’s deep mantle. While such studies show that the origin of positive seismic discontinuities are mostly attributed to phase transitions, temperature variations, and mineral composition of mantle rocks, the origin of anomalous zones—with low seismic velocities, widespread at multiple depths across the globe—remain much less understood. The mantle transition zone (MTZ) appears to be a very complex layer with seismic velocity increments at the main discontinuities (410’ and 660’) whereas velocities decrements, in addition to high attenuation, are observed in adjacent areas such as between 350-410 km depths atop 410’ and beneath 660.’ The MTZ marks the boundary between the upper and lower mantle and therefore plays a fundamental role in regulating mantle circulation, hence understanding the nature (e.g. mineral composition, presence/absence of melts, etc.) of seismological observations is essential to understand the material cycle of impurities such as water in the Earth's interior. Several hypotheses have been proposed to explain the observed seismic anomalies, among them, phase transitions associated with mantle temperature variations, the effect of chemistry, and mineralogy or the presence of partial. Here, I will present laboratory measurements of elastic wave velocities by ultrasonic interferometry combined with synchrotron x-ray techniques and the multianvil apparatus. I will show how these techniques are readily used to measure P- and S-wave velocities of mantle minerals and rock aggregates under simultaneous high-pressure and high-temperature, and how those data can be used to constrain the MTZ composition across its major seismic discontinuities. Then, I will show some recent advances for these techniques that allow for investigating the effect of partial melting on the elastic wave velocities of mantle rock aggregates and discuss how those data can be used to investigate anomalous seismic zones in the MTZ.

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