Fundamental Research in High Energy Density Science (2023) / Chapter Skim
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3 Opportunities and Grand Challenges
3 Opportunities and Grand Challenges
Pages 39-67
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From page 39... ...
Experiments and theory are intertwined in all three instances, with implications for disciplines ranging from astrophysics and chemistry to condensed-matter, materials, and plasma physics. GRAND CHALLENGES AND OPPORTUNITIES FOR HIGH ENERGY DENSITY SCIENCE Discoveries in HED science that transform the fabric of society materialize when breakthroughs in laboratory and computational technologies can test and put 1 Rather than the inherently negative "gaps" noted in the statement of task, the committee chose to use "opportunities" with the intent that the National Nuclear Security Administration (NNSA)
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From page 40... ...
How can burning fusion plasmas be controlled and harnessed for society's energy, security, and technology needs? Fundamental HED science is essential to the development of the technologies and processes required for controlling nuclear fusion in the laboratory, taking current experiments that are documenting the onset of nuclear ignition to the point of fully exploiting the output of nuclear reactions.
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A concerted effort is required, integrating experiments and advanced simulations, including artificial intelligence and machine learning for both quantum systems and multicomponent chemistry.
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A new generation of experiments and model ing, including simulation and theory, is beginning to define the linkages between these different scales, helping to characterize the stability of inertial confinement fusion (ICF) implosions; translating microscopic viscosity estimates to magnetic dynamo processes in planets; defining the strength of bulk matter; and correlating between kinetic, thermal, plasma-wave, Coulomb, and nuclear energy scales in the warm dense matter of low-mass stars.
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The energy density of such light already exceeds 1017 J m–3, sur passing by a million-fold the onset of the HED regime described in this report. In interacting with matter, this large energy density represents an enabling technology for HED applications.
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science and address future national needs, the NNSA should exploit and enhance the capabilities of its flagship HED facilities (e.g., the National Ignition Facility, Z Pulsed Power Facility, and Omega Laser Facility) by establishing plans over the next 5 years for (1)
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From page 45... ...
. Magnetically confined fusion experiments operate at low densities for long times, and inertial fusion experiments operate at high densities for short times; however, both must reach or exceed this simple product to produce net energy from fusion reactions.
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From page 46... ...
But ICF also offers unique opportunities for HED science itself -- the extreme temperatures, densities, and radiation fields created by an igniting plasma lead to new pressure–temperature–radiation regimes that cannot be accessed in other terrestrial environments. Finally, inertial fusion also has deep intellectual ties to stockpile stewardship, which has enabled the United States to maintain a safe, secure, and reliable nuclear weapons stockpile without nuclear explosion testing since 1992.
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From page 47... ...
Extending this density and temperature coverage will make possible extrapolation to yet more extreme conditions, such as those near the degeneracy boundary in white-dwarf stars. Oxygen opacity is a dominant issue for carbon-rich white dwarfs, and such experimental benchmarks will have a significant impact on stellar and white-dwarf modeling.
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From page 48... ...
Such condi tions are beyond current HED facilities, but during the past decade, HED facilities have explored nuclear properties by coupling hot plasma and nuclear processes in the laboratory. For example, cross-sections of nuclear processes measured using accelerators must be corrected for screening effects, which are dominant at collision energies relevant to nuclear processes in stellar environments, supernovae and big-bang nucleosynthesis (BBN)
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Creating conditions suitable for reliably characterizing laboratory experiments and material properties in this regime is a Grand Challenge. Non-Equilibrium Models and Analysis The vast majority of existing models and measurements assume that materials are in local thermodynamic equilibrium (LTE)
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. This is a significant gap because these are the only facilities capable of generating the most extreme HED conditions, including matter at atomic scale pressures and dense plasmas with significant fusion yield.
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. FIGURE 3-3 High-intensity laser beams that can now be controlled to unprecedented length and time scales enable future advanced high energy density sources Top: Traditional, nonlinear, Thomsonscattering configuration generates a divergent photon source (purple)
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Models that enforce these relationships and use them to constrain observables for comparison with data can enormously increase the impact of any single, high precision measurement. Opportunity: Hydrodynamic Properties In comparison with matter in other HED regimes, warm dense plasmas are characterized by relatively high densities and low temperatures.
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which makes it more viscous, in turn leading to faster dissipation. This positive feedback results in what has been theoretically predicted as a "sudden dissipation effect." The sudden dissipation, with sudden increase in temperature, could result in a sudden onset of nuclear fusion or intense radiation.
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Moreover, there is significant potential for plasma based X-ray "lasers," generated with compact laser pumps these would change dramatically the characterization capabilities for compression facilities. Finding: The technology of advanced, ultrashort pulsed sources (e.g., XFELs, compact plasma-based lasers, monoenergetic particle beams)
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when there is limited resolution in experimental measurements. Hence, simulation is crucial to the future of HED science, and increasing efforts in theory, simulation, and machine learning at universities and national laboratories is key to progress. The scope of traditional HED science funding can also be broadened to support the discovery of new materials (e.g., hydride superconductors)
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A broad developer base that includes experts with training in modern computing architectures could enormously benefit the field. Conclusion: Modernization of legacy computer codes, and the development of codes by the academic community, need to be systematically supported, including the development of strategies for sharing codes that leverage the experience gained by computational centers, such as those supported by the Department of Energy Basic Energy Sciences program3 in condensed-matter and materials science.
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It is essential to define physical models, from atomistic to continuum, including first principles and kinetic theory, to obtain robust comparisons. Finding: Machine learning and other artificial intelligence methods are emerg ing as powerful scientific tools.
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Increased efforts to integrate theory, experiment, computation, data sci ence, and machine learning have the potential for significant impact. Standards for machine learning and data bases are needed, with suitable efforts for adoption and adaptation by the research community.
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strategy for high energy density science over the next 2 years. This strategy should include benchmarking and the verification and validation of codes, code compari sons, the close integration of simulations using HPC with experiments, co development of hardware and software for the research community, open source documentation of codes and experimental results in a standardized open format (e.g., to enhance use and effectiveness of machine learning and artificial intelligence tools)
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This can also benefit from the comparison of computed results obtained using different physical models. Benchmarking: Establish well-defined reference points from theory and experiment, often the key step in verification and validation.
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Both uncertainty quantification of multi-physics codes and theory itself can be used to determine which materials and conditions are the most important for different HED applications. EXTREME HIGH ENERGY DENSITY SCIENCE: BEYOND WARM DENSE MATTER AND NUCLEAR FUSION Opportunity: Frontiers in High Energy Density Radiation and Particle Acceleration Pair Production State-of-the-art laser intensities of 1022 W cm−2 have energy densities on the order of 3 × 1017 J m−3, a million-fold greater than the onset of HED at 1011 J m−3.
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To reach the QED critical field for pair production, a 50 GeV electron-beam collides with a 1018 W/cm2 laser pulse. The e-beam has energy density of about 1015 J m−3, and the laser has energy density of about 1013 J m−3.
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From page 63... ...
The present report therefore focuses on HED involving matter rather than light, yet the committee emphasizes the fundamental importance of research on HED radiation fields. Interest in the HED radiation regime additionally stems from its role as an enabling technology for future experiments.
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A Klesman, 2019, "This Supermassive Black Hole Sends Jets Ricocheting Through Its Galaxy," Astronomy February 18, https://astronomy.com/news/2019/02/this-supermassive-black hole-sends-jets-ricocheting-through-its-galaxy.
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Notably, relativistic electron temperatures can now be produced and measured in subrelativistic laserplasma experiments, suggesting great promise for breakthroughs in laboratory astrophysics.4 Conclusion: There is a great opportunity for discovering the behavior of HED matter in extreme fields, including radiation and velocity as well as temperature and density. Opportunity: Nuclear Reactivities in HED Matter Astrophysically relevant nuclear reactions are just now beginning to be studied using inertial confinement fusion (ICF)
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h i n H i In g h Section E n e r g3, y we Density Science ust be emphasized that the pyc- estimate the fusion rate by WKB method and show ction itself is generally accepted that the pycnonuclear reactions might be observable general acceptance has not been in an experiment. In Section 4, we show the fusion ffects to which it has been asso- rate is further enhanced by electron screenings.
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From page 67... ...
To do this project, we were going to need a very intense laser to force the interaction between the ions and a large number of photons, and such a laser did not yet exist. Gerard and I developed a new laser technology, now known as chirped pulse amplification (CPA)
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