In 2017, the High Energy Density Science (HEDS) Center launched a HEDS seminar series at Lawrence Livermore National Laboratory. Contact grabowski5 [at] llnl.gov (Paul Grabowski) for more information.
All presentations are the works of the speakers and owned by their respective institutions. We thank the speakers for permission to post their work here.
Plasma-based Amplification and Manipulation of High-power Laser Pulses
In the last decade, the increasing availability of terawatt- and petawatt-class lasers with pulse durations on the order of 10 to 100 femtoseconds has intensified interest in the relativistic interaction between laser radiation and matter. Today laser intensities up to 1022 W/cm2 can be achieved. Most high-intensity lasers today rely on amplification schemes that can barely be scaled to higher power levels due to material damage thresholds. An alternative approach that allows circumventing these issues is the use of plasma as an amplification medium. In the presentation, Prof. Lehmann discusses Brillouin-type plasma-based laser amplifiers and show that the ion plasma waves, driven by the two laser pulses, eventually form photonic crystals.
The Relaxation Cascade in Driving High-Energy Density Matter
High-energy-density matter (HEDM) in the laboratory is usually created in states far from equilibrium as the large energy input needed for ionization and heating drives particles into specific states and distributes the energy unevenly between the species. The pathways to equilibrium, or at least the relaxation times, are therefore very important for interpreting most experiments. This talk will review the different stages of the equilibration process that span the time scales from femtoseconds, for establishing an equilibrium distribution for the electrons, to nanoseconds, for material rearrangements. Special focus is given to the effects of strong interactions inherent to HEDM. Finally, the nonequilibrium physics discussed is applied to a number of recent experiments.
Department of Physics and Astronomy, UC Irvine
September 14, 2017
Ultrafast Laser-driven Probes for Investigating High Energy Density Physics
Intense laser-plasma interactions are a robust source of radiation pertinent for investigating matter in extreme conditions, as evidenced by the Matter in Extreme Conditions beamline at the SLAC National Accelerator Laboratory and the Advanced Radiographic Capability beamline at NIF. Experiments showcasing the use of short-pulse lasers to create bright soft x-rays with circular helicity, white-light spectrum radiation suitable for near-edge x-ray absorption fine structure radiography, and radiography using high-energy electrons will be presented. Dynamic measurements of nano-plasmas will also be presented.
School of Engineering and Applied Science, Princeton University
August 31, 2017
Quantum mechanics–derived computer simulations can provide insights into the survivability of first-wall and divertor materials in prototype magnetic confinement fusion reactors. I present results of research aimed at assessing how hydrogen isotopes interact with solid tungsten and liquid lithium, candidates for plasma-facing components of fusion reactors. The research utilizes both standard Kohn-Sham density functional theory (KS-DFT) as well as orbital-free (OF) DFT. Over the last two decades, my research group has advanced the latter theory in terms of accuracy and efficiency. Our open-source code PROFESS exhibits quasilinear scaling with a small prefactor, rendering it orders of magnitude faster than KSDFT, thereby enabling significantly larger system-size (static and dynamic) simulations. The method also now works on leadership-class petascale computers (Titan at ORNL). However, OFDFT relies on kinetic energy density functionals, which at this point are still only as accurate as KSDFT for main group semiconductors and metals. Ongoing work aims to alleviate this problem, which ultimately should extend OFDFT to the rest of the periodic table.
Department of Physics and Astronomy, Stony Brook University
August 10, 2017
The seminar will describe ongoing simulations of Type Ia supernovae and x-ray bursts. Type Ia supernovae are the brightest thermonuclear explosions in the present-day universe, and are important for nucleosynthesis and measuring distances in cosmology. To date, however, there is no consensus on what the pre-explosion system looks like. The popular progenitor models, along with their strengths and weaknesses, will be discussed, along with the work being done to understand them. X-ray bursts provide a different set of challenges to the modeler, but ultimately, they can help us understand the nuclear equation of state. Stony Brook’s simulations use the publicly-available adaptive mesh refinement codes Castro and Maestro, built on the AMReX library. Maestro models subsonic stellar flows, while Castro focuses on highly-compressible flows. These codes share the same microphysics (reaction networks, equations of state) and parallelization strategy. In addition to the science results, the development of these codes for next generation architectures, including GPU-based supercomputers, will be discussed.
Departments of Physics and Astronomy and Electrical Engineering, University of California at Los Angeles
July 27, 2017
Exaflop, Petawatt, and Terabar Physics
Exaflop (1018 flop) computers are on the horizon. These computers are complex and expensive instruments that require significant preparation in developing software and analysis methods to use effectively. They have the potential to dramatically advance the rate of scientific discovery. Two areas where petaflop computers are impacting plasma physics research are plasma-based acceleration and the nonlinear optics of plasmas, both of which are part what is called high-energy-density (HED) plasma physics. In plasma-based acceleration, electrons or positrons surf plasma wave wakes excited by petawatt lasers or particle beams at rates in excess of 50 GeV/m (three orders of magnitude higher than current accelerator technology). At the National Ignition Facility (NIF), the fuel is to be compressed to hundreds of gigabars of pressure, causing ignition. It is essential that the laser energy hit and be absorbed into x-rays where it is aimed for such compression to be achieved.
Leung Center for Cosmology and Particle Astrophysics, National Taiwan University
July 20, 2017
Tabletop Analog Black Holes to Investigate Information-Loss Paradox
The question of whether Hawking evaporation violates unitarity, and therefore results in the loss of information, remains unresolved since Hawking's seminal discovery in 1974. So far the investigations remain mostly theoretical, as it is almost impossible to resolve this paradox through direct astrophysical black-hole observations. The seminar will describe how relativistic plasma mirrors can be accelerated drastically and stopped abruptly by impinging ultra-intense x-ray pulses on solid plasma targets with a density gradient. This is analogous to the late-time evolution of black-hole Hawking evaporation. An experimental concept will be proposed, and a self-consistent set of physical parameters is presented. Critical issues such as black-hole unitarity may be addressed through the measurement of the entanglement between the Hawking radiation and partner modes.
Department of Mechanical and Aerospace Engineering, University of California at San Diego
June 29, 2017
Fast Ignition: The Good, the Bad, and the Ugly
The fast ignition (FI) concept for inertial confinement fusion (ICF) has the potential to provide a significant advance in the technical attractiveness of inertial fusion energy. In FI, compression of the fuel to high density and heating are achieved in separate processes. Similar to conventional ICF, a number of long-pulse lasers compress a shell to create a high-density fuel plasma. The requirements on the symmetry of the target are less stringent in FI compared to conventional ICF due to the external heating source. In addition, higher gain is expected with the FI scheme because more fuel mass can be burned with less compression energy. This scheme involves some of the most challenging and complex physics of laser-matter interactions and energetic particle transport in varying density plasmas. In recent experiments and modeling, critical issues pertinent to electron source, transport through plasma, and target design have been identified. Experimental and integrated modeling provided detailed characterization of these issues and enabled validated measurements of total coupling of the laser energy to the compressed core.
SLAC National Accelerator Laboratory
May 25, 2017
Visualizing the Transformation of Matter in Extreme Conditions
At the SLAC National Accelerator Laboratory, we have developed powerful ultrafast pump-probe techniques to measure the structural transformations and the physical properties of matter in extreme conditions. We apply enormous pressures to our samples using high-power laser irradiation followed by x-ray laser pulses from the Linac Coherent Light Source to take split-second photographs of the states that result. This seminar describes our experiments that visualize compression, solid-solid phase transitions, and the formation of warm dense matter. These experiments deliver data of unprecedented accuracy that allow critical experimental tests of theory in the challenging near-Fermi degenerate regimes or in the non-ideal plasma state. Recently, we complemented our x-ray probing capability with high-energy electron diffraction techniques to investigate isochorically laser-heated matter. This data set holds surprises; our results do not support previous claims about bond hardening in warm dense matter and resolve previously undetermined melting regime boundaries.
Department of Earth and Planetary Sciences, University of California at Davis
May 11, 2017
Following the multicomponent phase diagram to the origin of the Moon
The giant impact hypothesis remains the leading theory for lunar origin. However, current models struggle to explain the Moon’s composition and isotopic similarity with Earth. Here we present a new lunar origin model. High-energy, high-angular momentum giant impacts can create a post-impact structure that exceeds the corotation limit (CoRoL), which defines the hottest thermal state and angular momentum possible for a corotating body. In a typical post-CoRoL body, traditional definitions of mantle, atmosphere and disk are not appropriate, and the body forms a new type of planetary structure, named a synestia. Using simulations of cooling synestias combined with dynamic, thermodynamic, and geochemical calculations, we show that satellite formation from a synestia can produce the main features of our Moon. The key to lunar origin is understanding the high energy density state of the Earth after a giant impact.
Department of Physics and Astronomy, University of California at Irvine
April 27, 2017
X-ray Wakefield Accelerator on a Chip
It is well established that an intense optical laser pulse can drive coherent and stable wakefields that can accelerate electrons to high energies in plasmas. The recent inventions of thin film compression of lasers and its associated relativistic compression can lead to the generation of a single-cycled optical laser pulse and its relativistically compressed single-cycled x-ray laser pulse. This introduces the possibility of an x-ray laser-driven wakefield now in materials at the solid density. We suggested nanoholed material as a possible medium. The nanoholed channel allows well collimated wakefields and avoids unnecessary collisions for the accelerated beam. Further, a corrugated nanochannel could result in wakefield-driven gamma-ray sources. Because the accelerating media in nanomaterials are now in a solid (rather than in a gas), it is easy to design the structure, although rastering over many holes may be necessary. Such precision design should further allow us to pick up ions, such as by the phase velocity gradation; or the single-cycled property of the laser could make ion acceleration more coherent.
Departments of Earth and Planetary Science, University of California, Berkeley
April 20, 2017
Path Integral Monte Carlo Simulations of Warm Dense Matter
The properties of materials at extreme pressure and temperature conditions are important in astrophysics and fusion science. When models for Jupiter’s interior are constructed to match gravity data from the NASA mission Juno, an accurate knowledge of the equation of state of hydrogen–helium mixtures is essential. Modern dynamic high pressure experiments typically probe megabar and gigabar pressures. In order to provide a comprehensive theoretical description of materials at such extreme conditions, results from path integral Monte Carlo simulations will be presented. Equation of state results for first-row elements including carbon, CH plastic, oxygen, water, nitrogen, and neon were derived with restricted path calculations that relied on free-particle nodes. Shock Hugoniot curves were computed and compared with experimental results. The talk will describe how bound states can be incorporated efficiently into the nodal structure, which enables the simulation of heavier elements, including sodium and silicon.
Departments of Physics and Chemistry, UC Irvine
March 2, 2017
Improving Simulations of Warm Dense Matter by Developing Thermal Density Functional Theory
In the past decade or so, quantum molecular dynamics—simulations of classical ions coupled to density functional theory (DFT) calculations for electrons—have provided unprecedented quantitative agreement between simulation and measurement for warm dense matter and tremendous insight into equilibrium and near-equilibrium processes. Routine calculations use modern density functional approximations that neglect thermal many-body effects. The talk will summarize recent efforts to generalize much ground-state DFT methodology to calculations at finite temperatures.