Fundamental Research in High Energy Density Science (2023) / Chapter Skim
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2 Recent Progress and Opportunities
2 Recent Progress and Opportunities
Pages 19-38
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. Finding: HED science has produced spectacular advances in basic science (see, e.g., Table 2-1 and Box 2-3)
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184503 PNAS 105 (2008) 11071 Crystalline metallic oxygen characterized PRL 102 (2009)
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862 NOTE: ApJ, Astrophysical Journal; ARCMP, Annual Review of Condensed Matter Physics; PNAS, Proceedings of the National Academy of Sciences; PRE, Physical Review E; PRL, Physical Review Letters; RSI, Review of Scientific Instruments; Sci Adv, Science Advances. PHYSICS AND MATERIALS: MATTER MANIPULATION ON THE QUANTUM SCALE Pressure Metallization and Un-metallization One of the most dramatic effects of pressure is the transformation of many chemical elements and compounds into the metallic state, characterized by high electrical conductivity, as well as high opacity to and reflectivity of visible light.
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The dashed lines labeled Jupiter and Sun show the conditions of temperature and pressure within those bodies; ICF (inertial confinement fusion) indicates the conditions of a capsule undergo ing laser compression.
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The metallization of carbon, theoretically predicted and supported by experimental results, may limit diamond-anvil cells to maximum pressures of about 1 TPa. The reason that pressure tends to metallize elements and compounds is that as atoms are squeezed together, their electrons tend to avoid each other, both because the negatively charged electrons repel one another and for quantum mechanical reasons (see Figure 2-1)
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, thereby pinning down the electrons and transforming the metal to a non-metallic state. Each atom consists of a positively charged nucleus (dark blue point)
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, and the most accurate dynamic experiments use magnetic- or laser-driven planar compression to achieve 2-10 TPa, respectively. These experiments provide some of the first experimental checks of "statistical atom" theory that is widely used to understand the interiors of stars and giant planets, confirming as well as extending these atomic models (e.g., Thomas-Fermi-Dirac theory)
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cold compression of atoms to the point that their core electron orbitals begin to combine and hybridize, and (2) compres sion at high enough temperatures that electronic transitions occur between inner atomic core orbitals or mixed core and outer orbitals (see Figure 2-2-1)
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at which chemical bonding is changed, from static compression using diamond-anvil cells to mechanical impact and laser- and magnetic-driven dynamic compression. Finding: High-quality measurements are possible well into the HED regime, to 0.5-1 TPa statically, and to 1-10 TPa through shock or ramp loading; pio neering laboratory measurements are exploring the 10-100 TPa (0.1-1 billion atmosphere)
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The difficulty of calculations, which require not only extensive atomic structure but also dense-plasma effects, is compounded by the relatively few atomic physicists who focus on HED conditions. The recent experimental measurement of iron opacity was therefore widely considered a major contribution, not only as a technical accomplishment -- the fact that the opacity of ionized iron could be successfully measured -- but also because it helps address a problem in understanding the Sun's composition.
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Another perspective on HED science addresses the role of impacts during the gravitational accumulation of mass as a planet forms. Typical orbital velocities around the Sun show that impacts associated with planet formation generate terapascal-scale pressures; that is, create HED conditions at the planet's growing surface.
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REDEFINING CHEMICAL BONDS Low-Temperature Plasma and Electrochemistry The electron distributions between atoms define the chemical bonds in a molecule, solid, liquid, or gas, determining the physical and chemical properties of matter. Not only do HED conditions of high pressure and temperature reshape the distribution of electrons between atoms, relative to ambient conditions, but the electromagnetic fields used to achieve these conditions in laboratory experiments also contribute to changing the electron clouds around atoms.
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, and evidence of significant energy being released in ICF experiments is among the most exciting recent breakthroughs in HED science. For the first time, more energy has been produced by nuclear fusion than was directly accessible to the material being compressed.
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Finding: NIF, Omega, and Z, the major NNSA HED laser and pulsed-power facilities, are producing breakthrough science, including through their external user programs for Discovery Science. Targets One of the key enabling technologies for performing HED science is the targ etry, which is required in virtually all experiments.
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Patel, R Betti, et al., "Physics Principles of Inertial Confinement Fusion (ICF)
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Energy yield of 3.15 MJ Target gain ~1.5 3 2.05 MJ of laser energy Fusion Energy Yield (MJ) 2 Max laser energy 1 0 2012 2014 2016 2018 2020 2022 Year FIGURE 2-3-1 Researchers have made huge strides in producing energy from nuclear fusion in the laboratory, with the bar colors representing different design approaches used at the National Ignition Facility.
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The significance of HED science is that it greatly enhances the quantum regime of superconductivity, with several room-temperature superconductors having now been discovered at high pressures. In particular, hydrogen-rich compounds are found to exhibit superconductivity at the highest of temperatures, consistent with current HED understanding of hydrogen itself -- these crystalline metal hydrides apparently exhibit some of the exotic quantum properties expected for metallic atomic hydrogen.
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The figure shows experimentally measured superconducting transition temperatures as a function of time, with room temperature superconductors having been discovered above 180 GPa pressure by 2020. Although currently synthesized at high pressures, research suggests that it is possible to produce room temperature superconductors at or near ambient conditions.
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In short, HED science spun off the modern $500 billion per year computer micro-chip manufacturing industry based on EUV lithography, and the reason that the United States is home to the majority of EUV lithography tools is because of this specific program emerging from the national laboratories and the support provided by it. controlled as a function of pressure and deformation.
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The increasing fidelity, flexibility, and reliability of these critical tools -- and the underlying experiments -- is one of the triumphs of HED science. Finding: The integration of approaches from theory, simulation, and experi mentation is critical in the HED regimes, for which the multiplicity of time and lengths scales leads to challenges in understanding basic material properties and macroscale system behavior.
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