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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Fluorescence and absorption spectroscopy for warm dense matter studies and ICF plasma diagnostics

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. In this work, we show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated by the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Lastly, analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 10 24 e/cm 3 ) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

A technique for extending by ∼10{sup 3} the dynamic range of compact proton spectrometers for diagnosing ICF implosions on the National Ignition Facility and OMEGA

Wedge Range Filter (WRF) proton spectrometers are routinely used on OMEGA and the NIF for diagnosing ρR and ρR asymmetries in direct- and indirect-drive implosions of D{sup 3}He-, D{sub 2}-, and DT-gas-filled capsules. By measuring the optical opacity distribution in CR-39 due to proton tracks in high-yield applications, as opposed to counting individual tracks, WRF dynamic range can be extended by 10{sup 2} for obtaining the spectral shape, and by 10{sup 3} for mean energy (ρR) measurement, corresponding to proton fluences of 10{sup 8} and 10{sup 9} cm{sup −2}, respectively. Using this new technique, ρR asymmetries can be measured during both shock and compression burn (proton yield ∼10{sup 8} and ∼10{sup 12}, respectively) in 2-shock National Ignition Facility implosions with the standard WRF accuracy of ±∼10 mg/cm{sup 2}.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Nuclear diagnostics for Inertial Confinement Fusion (ICF) plasmas

The field of nuclear diagnostics for Inertial Confinement Fusion (ICF) is broadly reviewed from its beginning in the seventies to present day. During this time, the sophistication of the ICF facilities and the suite of nuclear diagnostics have substantially evolved, generally a consequence of the efforts and experience gained on previous facilities. As the fusion yields have increased several orders of magnitude during these years, the quality of the nuclear-fusion-product measurements has improved significantly, facilitating an increased level of understanding about the physics governing the nuclear phase of an ICF implosion. The field of ICF has now entered an era where the fusion yields are high enough for nuclear measurements to provide spatial, temporal and spectral information, which have proven indispensable to understanding the performance of an ICF implosion. At the same time, the requirements on the nuclear diagnostics have also become more stringent. To put these measurements into context, this review starts by providing some historical remarks about the field of ICF and the role of nuclear diagnostics, followed by a brief overview of the basic physics that characterize the nuclear phase and performance of an ICF implosion. A technical discussion is subsequently presented of the neutron, gamma-ray, charged-particle and radiochemistry diagnostics that are, or have been, routinely used in the field of ICF. This discussion is followed by an elaboration of the current view of the next-generation nuclear diagnostics. Since the seventies, the overall progress made in the areas of nuclear diagnostics and scientific understanding of an ICF implosion has been enormous, and with the implementation of new high-fusion-yield facilities world-wide, the next-generation nuclear diagnostics will play an even more important role for decades to come.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Exploring Sensitivity of ICF Outputs to Design Parameters in Experiments Using Machine Learning

We report building a sustainable burn platform in inertial confinement fusion (ICF) requires an understanding of the complex coupling of physical processes and the effects that key experimental design changes have on implosion performance. While simulation codes are used to model ICF implosions, incomplete physics and the need for approximations deteriorate their predictive capability. Identification of relationships between controllable design inputs and measurable outcomes can help guide the future design of experiments and development of simulation codes, which can potentially improve the accuracy of the computational models used to simulate ICF implosions. In this article, we leverage developments in machine learning (ML) and methods for ML feature importance/sensitivity analysis to identify complex relationships in ways that are difficult to process using expert judgment alone. We present work using random forest (RF) regression for prediction of yield, velocity, and other experimental outcomes given a suite of design parameters, along with an assessment of important relationships and uncertainties in the prediction model. We show that RF models are capable of learning and predicting on ICF experimental data with high accuracy, and we extract feature importance metrics that provide insight into the physical significance of different controllable design inputs for various ICF design configurations. These results can be used to augment expert intuition and simulation results for optimal design of future ICF experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Degradation of performance in ICF implosions due to Rayleigh–Taylor instabilities: A Hamiltonian perspective

The Rayleigh–Taylor instability (RTI) is an ubiquitous phenomenon that occurs in inertial-confinement-fusion (ICF) implosions and is recognized as an important limiting factor of ICF performance. To analytically understand the RTI dynamics and its impact on ICF capsule implosions, we develop a first-principle variational theory that describes an imploding spherical shell undergoing RTI. The model is based on a thin-shell approximation and includes the dynamical coupling between the imploding spherical shell and an adiabatically compressed fluid within its interior. Using a quasilinear analysis, we study the degradation trends of key ICF performance metrics (e.g., stagnation pressure, residual kinetic energy, and areal density) as functions of initial RTI parameters (e.g., the initial amplitude and Legendre mode), as well as the 1D implosion characteristics (e.g., the convergence ratio). We compare analytical results from the theory against nonlinear results obtained by numerically integrating the governing equations of this reduced model. Our findings emphasize the need to incorporate polar flows in the calculation of residual kinetic energy and demonstrate that higher convergence ratios in ICF implosions lead to significantly greater degradation of key performance metrics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Extensions of a classical mechanics “piston-model” for understanding the impact of asymmetry on ICF implosions: The cases of mode 2, mode 2/1 coupling, time-dependent asymmetry, and the relationship to coast-time

As long suspected, low mode asymmetry in inertially confined fusion (ICF) implosions has been implicated as a performance limiting factor [Casey et al., “Evidence of three-dimensional asymmetries seeded by high-density carbon-ablator nonuniformity in experiments at the national ignition facility,” Phys. Rev. Lett. 126, 025002 (2021)]. Recently a non-linear, but solvable, theory [Hurricane et al., “An analytic asymmetric-piston model for the impact of mode-1 shell asymmetry on ICF implosions,” Phys. Plasmas 27, 062704 (2020)] based upon the simple picture of a pair of asymmetric pistons has generated new insights and provided some practical formulas for estimating the degradation of an implosion due to mode-1 asymmetry and demonstrated a previously unrecognized connection between measured hot-spot drift velocity, nuclear down-scatter ratio asymmetry, and the concept of residual kinetic energy (RKE). Asymmetry of the implosion “shell,” as opposed to asymmetry of the hot-spot, was key to the classical mechanics model because the majority of the kinetic energy in an implosion is carried by the shell. Herein, the two-piston model is extended to a six-piston model in order to capture mode-2 asymmetry and coupling between mode-1 and mode-2. A key result of this new six-piston model is that the weighted harmonic mean of shell areal density is the fundamental quantity that determines the RKE and performance degradations for a three-dimensional implosion. Agreement is found between the scalings coming from the theory and ICF implosion data from the National Ignition Facility and to large ensembles of detailed simulations. The connection between the piston model's dependence upon the radius of peak velocity and coast-time is also highlighted in this paper. Finally, by extending the two-piston model to include time-dependent “swing,” it is shown in the Appendix that the shell asymmetry at the time of stagnation dominates the solution for RKE.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Double cylinder target design for study of hydrodynamic instabilities in multi-shell ICF

Cylindrical implosions are used to study hydrodynamic instability growth for inertial confinement fusion (ICF) applications, as the cylindrical geometry allows for easier diagnostic access while retaining convergence effects. In this work, we use the established cylindrical implosion platform [Palaniyappan et al., Phys. Plasmas 27, 042708 (2020)] to inform the double shell ICF campaign [Montgomery et al., Phys. Plasmas 25, 092706 (2018)]. We present a design for a double cylindrical target as an analogue to the double shell ICF capsule in order to study hydrodynamic instability growth on the high-Z inner shell. Our design work is done with two-dimensional (2D) Eulerian radiation-hydrodynamics simulations, considering the axial uniformity of the implosion and feasibility of measuring the instability growth of pre-seeded single mode sinusoidal perturbations. We discuss in depth the design for a target to be directly driven at the OMEGA laser facility [Boehly et al., Opt. Commun. 133, 495 (1997)]. We evaluate the design for axial implosion symmetry and visibility of instability growth using synthetic radiographs constructed from the simulations, as the instability growth on the inner cylinder is experimentally measured using x-ray radiography of the implosion. We find that the seeded perturbation growth on the inner cylinder should be visible in an experiment, even with axial implosion asymmetry and preheat. We compare our 2D simulations with linear theory predictions for perturbation growth and show that a cylinder with lower azimuthal mode number (mode-20) perturbations compares more favorably with linear theory, while a cylinder with higher azimuthal mode number (mode-40) perturbations at the same starting amplitude saturates and is over-predicted by linear theory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Modeling ablator grain structure impacts in ICF implosions

High-density carbon is a leading ablator material for inertial confinement fusion (ICF). This and some other ablator materials have grain structure which is believed to introduce very small-scale (~nm) density inhomogeneity. In principle, such inhomogeneity can affect key ICF metrics like fuel compression and yield, by, for example, acting as a seed for instabilities and inducing mix between ablator and fuel. However, assessments of such effects are uncertain due to the difficulty of modeling this small-scale structure in ICF simulations, typically requiring reduced-resolution modeling that scales these features. We present a grain model and show both the impact of de-resolving grains and the complex mixing dynamics such structures can induce. We find that different methods for de-resolving grains can yield both different total deposition of kinetic energy perturbations and different fuel–ablator mixing. We then show a simple-to-implement approach for approximately conserving the deposition of perturbed kinetic energy and demonstrate that, for the present grain model and test cases, this approach yields a reasonably matched time history of mix width between less and more resolved grain models. The simulations here also demonstrate the complex interaction history between grain-induced mixing and instability around the fuel–ablator interface, showing, for example, that the grain-induced perturbations typically trigger instability of conduction-driven density gradients in the DT fuel, enhancing mix penetration early in the acceleration of the shell. Furthermore simulating both microscale and nanoscale grains, we find initial evidence for larger mixing in the microscale case of the present model, despite smaller deposited kinetic energy perturbation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Kinetic physics in ICF: present understanding and future directions

Kinetic physics has the potential to impact the performance of indirect-drive inertial confinement fusion (ICF) experiments. Systematic anomalies in the National Ignition Facility implosion dataset have been identified in which kinetic physics may play a role, including inferred missing energy in the hohlraum, drive asymmetry in near-vacuum hohlraums, low areal density and high burn-averaged ion temperatures (T i ) compared with mainline simulations, and low ratios of the DD-neutron and DT-neutron yields and inferred T i . Several components of ICF implosions are likely to be influenced or dominated by kinetic physics: laser-plasma interactions in the LEH and hohlraum interior; the hohlraum wall blowoff, blowoff/gas and blowoff/ablator interfaces; the ablator and ablator/ice interface; and the DT fuel all present conditions in which kinetic physics can significantly affect the dynamics. This review presents the assembled experimental data and simulation results to date, which indicate that the effects of long mean-free-path plasma phenomena and self-generated electromagnetic fields may have a significant impact in ICF targets. Finally, simulation and experimental efforts are proposed to definitively quantify the importance of these effects at ignition-relevant conditions, including priorities for ongoing study.

42 ENGINEERING↗
DOE OSTI2017

Ion kinetic dynamics in strongly-shocked plasmas relevant to ICF

Implosions of thin-shell capsules produce strongly-shocked (M > 10), low-density (ρ ~1 mg/cc -1 ), high-temperature (T i ~keV) plasmas, comparable to those produced in the strongly-shocked DT-vapor in inertial confinement fusion (ICF) experiments. A series of thin-glass targets filled with mixtures of deuterium and Helium-3 gas ranging from 7% to 100% deuterium was imploded to investigate the impact of multi-species ion kinetic mechanisms in ICF-relevant plasmas over a wide range of Knudsen numbers (N K ≡ λ ii /R). Anomalous trends in nuclear yields and burn-averaged ion temperatures in implosions with N K > 0.5, which have been interpreted as signatures of ion species separation and ion thermal decoupling, are found not to be consistent with single-species ion kinetic effects alone. Experimentally inferred Knudsen numbers predict an opposite yield trend to those observed, confirming the dominance of multi-species physics in these experiments. In contrast, implosions with N K ~ 0.01 follow the expected yield trend, suggesting single-species kinetic effects are dominant. In conclusion, the impact of the observed kinetic physics mechanisms on the formation of the hotspot in ICF experiments is discussed.

42 ENGINEERING↗
DOE OSTI2016

Wetted foam liquid fuel ICF target experiments

We are developing a new NIF experimental platform that employs wetted foam liquid fuel layer ICF capsules. We will use the liquid fuel layer capsules in a NIF sub-scale experimental campaign to explore the relationship between hot spot convergence ratio (CR) and the predictability of hot spot formation. DT liquid layer ICF capsules allow for flexibility in hot spot CR via the adjustment of the initial cryogenic capsule temperature and, hence, DT vapor density. Our hypothesis is that the predictive capability of hot spot formation is robust and 1D-like for a relatively low CR hot spot (CR~15), but will become less reliable as hot spot CR is increased to CR>20. Simulations indicate that backing off on hot spot CR is an excellent way to reduce capsule instability growth and to improve robustness to low-mode x-ray flux asymmetries. In the initial experiments, we will test our hypothesis by measuring hot spot size, neutron yield, ion temperature, and burn width to infer hot spot pressure and compare to predictions for implosions with hot spot CR's in the range of 12 to 25. Larger scale experiments are also being designed, and we will advance from sub-scale to full-scale NIF experiments to determine if 1D-like behavior at low CR is retained as the scale-size is increased. The long-term objective is to develop a liquid fuel layer ICF capsule platform with robust thermonuclear burn, modest CR, and significant α-heating with burn propagation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

The ICF syndrome protein CDCA7 harbors a unique DNA binding domain that recognizes a CpG dyad in the context of a non-B DNA

CDCA7, encoding a protein with a carboxyl-terminal cysteine-rich domain (CRD), is mutated in immunodeficiency, centromeric instability, and facial anomalies (ICF) syndrome, a disease related to hypomethylation of juxtacentromeric satellite DNA. How CDCA7 directs DNA methylation to juxtacentromeric regions is unknown. Here, we show that the CDCA7 CRD adopts a unique zinc-binding structure that recognizes a CpG dyad in a non-B DNA formed by two sequence motifs. CDCA7, but not ICF mutants, preferentially binds the non-B DNA with strand-specific CpG hemi-methylation. The unmethylated sequence motif is highly enriched at centromeres of human chromosomes, whereas the methylated motif is distributed throughout the genome. At S phase, CDCA7, but not ICF mutants, is concentrated in constitutive heterochromatin foci, and the formation of such foci can be inhibited by exogenous hemi-methylated non-B DNA bound by the CRD. Binding of the non-B DNA formed in juxtacentromeric regions during DNA replication provides a mechanism by which CDCA7 controls the specificity of DNA methylation.

Science & Technology - Other Topics↗
DOE OSTI2012

LANL Campaign 10 (ICF) FY2012 Year-End Highlights

The Los Alamos ICF program focused on ignition experiments and modeling and the continued development of HED experiments using both Omega and NIF. The first LANL ICF experiments on NIF took place in July for the DIME campaign. Diagnostic development for neutron imaging, gamma reaction history, and radiochemistry continued, also with experiments at NIF and Omega. The Trident laser facility supported the ICF, Science, and HEDLP programs by providing 550 shots to twelve different user groups.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Development of ICF Mix Code

Our project over the summer of 2012 was to develop an ICF mix code. The code we developed is a simplified arbitrary Lagrange Eulerian (ALE) method written from scratch in C++ and is designed to run on unstructured grids. We have performed initial verification of our code, comparing to analytical solutions of a Sod-like shock tube problem and the Sedov blast wave problem. The code was then extended to 2D and verified with respect to the 1D solutions. We also show the capability of our code to handle turbulent instabilities, such as Richtmyer-Meshkov (RM), which are commonplace within ICF experiments. Finally we present an ICF-like initial condition setup in our 1D Lagrange Hydro code.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Developing Quantum Levitation of ICF Capsules Coated with MgB 2 Thin Films

Current inertial confinement fusion (ICF) capsule support technologies create implosion perturbations which reduce fusion yield, driving the search for new support paradigms. Quantum levitation of the capsule will eliminate the requirement of a physical support structure, increasing fusion yield. The application of an external magnetic field to a capsule coated with a superconducting film can provide the necessary conditions for levitation. Magnesium diboride (MgB 2 ) is an attractive option for ICF applications as it has a high reported superconducting transition temperature of 39 K and is a low Z compound. This project is part of an ongoing effort which seeks to coat ICF capsules with a thin layer of superconducting MgB 2 . This project studied the synthesis of MgB 2 and diffusion/reaction kinetics of B/Mg/B m ultilayer thin films. These films were sputter deposited on flat glassy carbon substrates. Films were annealed in a tube furnace at temperatures between 400 °C and 650 °C for a total of 29 hours with film characterization done at predetermined intervals. At each interval, superconducting properties of the samples were evaluated with superconducting quantum interference device (SQUID) magnetometry, while Rutherford backscattering (RBS) with 2 MeV 4 He + ions was done to determine the composition and depth profile of the films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize surface morphology. Superconducting behavior was observed in thin films annealed at and above 450 °C. Formation of superconducting MgB 2 at 450 °C h as not been previously reported below 500 °C. The surface of the samples annealed at 500 °C and below was smooth with a measured roughness of ~3 nm. After 29 hours of annealing time, the 450 °C sample had a transition temperature of 27.3 K. The highest transition temperature measured was 30.9 K and was associated with a sample annealed for 29 hours at 650 °C. Transition temperatures were weakly positively correlated with annealing temperature and showed dependence on initial structural quality and oxygen contamination. Current research is attempting to synthesize superconducting MgB 2 coatings on spherical Si beads with the findings of this study. Future efforts are focused on the construction and testing of a levitation apparatus.

36 MATERIALS SCIENCE↗
DOE OSTI2025

60 years of science in ICF: from conception to scientific breakeven on the National Ignition Facility

The recent achievements of a burning plasma, fusion ignition, and scientific energy gain with deuterium-tritium (DT) fuel at Lawrence Livermore National Laboratory’s National Ignition Facility (NIF) represents a major milestone in the development of inertial confinement fusion (ICF) and all of fusion research. In these experiments, fuel pressures well in excess of hundreds of GBars were achieved in the compressed fuel, and robust alpha heating of the fuel, far in excess of the energy provided by the implosion, were demonstrated for the first time. These achievements occurred 60 years after the inception of ICF and the first laser demonstration, and were made possible by more than five decades of research at laser facilities around the world. Advances in laser technology both in wavelength and precision, motivated by improved understanding of laser-plasma interaction physics and the demands of targets; improvements in target fabrication inspired by the need to control and minimize hydrodynamic instabilities in the implosion; and multi-dimensional simulations and diagnostics have been critical to this achievement. This paper will summarize the scientific and technical advances, the surprises, and the challenges that had to be overcome to achieve these goals.

fusion↗