These are a few of the Laboratory's achievements during 2016 in ST&E.
Updated November 16th, 2016
A recent experiment conducted on the Janus laser at Livermore’s Jupiter Laser Facility has established the feasibility of plasma-based lasers. Such devices, based on the interaction of plasma—a medium consisting of freely moving ions and free electrons—and lasers, are ultrafast, more damage-resistant than conventional optics, and easily tunable. Developing high-power lasers with greater control over beam characteristics is essential to Livermore’s pursuit of inertial confinement fusion (ICF), and science-based stockpile stewardship to ensure the safety and reliability of the nuclear deterrent.
In a Physical Review Letters paper published online on May 18, 2016, Livermore researchers and colleagues report on the first experimental demonstration of a high-power plasma wave plate, a device used to modify the polarization, or electric-field orientation, of an independent probe laser beam. The experiment indicates that high-power, tunable laser–plasma photonic devices operating at intensities millions of times greater than those withstood by traditional (crystal-based) optics are possible. The work could have an impact on laboratory astrophysics and particle accelerators as well as on inertial confinement fusion experiments at Livermore’s National Ignition Facility—plasma-based optical components could be used to redirect, focus, and improve the contrast of laser beams, to tune the implosion symmetry of ICF targets by facilitating power transfer between intense lasers and other components. The Laboratory Directed Research and Development (LDRD) supported this research.
For the first time, Livermore researchers have shown that carbon nanotubes as small as 0.8 nanometers diameter can transport protons faster than bulk water, by an order of magnitude. The research validates a 200-year-old mechanism of proton transport. The transport rates in these nanotube pores, which form one-dimensional water wires, also exceed those of biological channels and man-made proton conductors, making carbon nanotubes the fastest known proton conductor. The research appears in the April 4, 2016, online edition of the journal Nature Nanotechnology.
When water is forced into the nanotube, protons move through that water even faster than through normal or bulk water. Livermore scientists used carbon nanotube pores to line up water molecules into perfect one-dimensional chains. The proton motive force is a major factor in many biological processes such as energy production and storage in bacteria, and respiration. Unfortunately, synthetic proton conductors have lagged behind their biological counterparts because of the difficulty of forming and maintaining the structured one-dimensional water chains that enable proton hopping. The Livermore research could advance the development of practical applications such as improved proton exchange membranes in fuel cells, proton-based signaling in biological systems, and the emerging field of proton bioelectronics (protonics). The U.S. Department of Energy’s Office of Basic Energy Sciences supported this work.
One of the key research goals at Livermore’s National Ignition Facility (NIF) is demonstrating inertial confinement fusion ignition for both stockpile stewardship and as a potential source of clean energy. A paper published in the April 11, 2016, online issue of the journal Nature Physics reviews recent progress towards this goal. In the paper, Livermore scientists and colleagues analyze the series of National Ignition Facility “high-foot” inertial confinement fusion (ICF) experiments conducted in 2013 and 2014 that reached the highest levels of alpha heating ever achieved on any laser facility. Alpha heating, or self-heating, is a key step on the path to ignition in which the deuterium–tritium fusion reaction products deposit their kinetic energy locally within the fusion reaction region, thus increasing the temperature there and continually reinforcing the reaction rate.
The alpha particle heating of the plasma dominated, with the produced fusion yield exceeding that of the work done by the compression of the fuel alone. Recent three-dimensional simulations of the fusion targets have shown reasonable agreement with the experimental results and suggest that an improved understanding of the implosions is emerging that can be used to guide future work. Current ICF experiments are working toward the goal of increasing implosion densities and temperatures by a factor of two to four, which researchers estimate is the threshold for ignition. The National Nuclear Security Administration funds NIF.
Livermore material scientists have found that 3D-printed foams have higher durability and better long-term mechanical performance than standard cellular materials. The research appears in the April 27, 2016, edition of Scientific Reports. Foams, also known as cellular solids, are an important class of materials with applications ranging from thermal insulation and shock-absorbing support cushions to lightweight structural and flotation components. Foams are essential in the automotive, aerospace, electronics, marine, biomedical, packaging, and defense industries. At Livermore, better foam materials through advanced materials and manufacturing research have applications to national security missions in such areas as stockpile stewardship science, and energy. Traditionally, foams are created by processes that lead to a highly non-uniform structure with significant variety in size, shape, thickness, connectedness, and topology of constituent cells.
To develop an improved alternative, Laboratory researchers demonstrated the feasibility of 3D-printing uniform foam structures through the direct-ink-write process. Their research examined the long-term mechanical stability of 3D-printed foams through accelerated aging experiments, subjecting samples of traditional foam and 3D-printed materials to elevated temperatures under constant compressive strain. They monitored the stress condition, mechanical response, and permanent structural deformation of each sample for one year or more, and quantitatively modeled the evolution of these properties over decades. The study convincingly demonstrated that 3D-printed materials age slowly—they better retain their mechanical and structural characteristics compared to their traditional counterparts.
In a paper published in the April 15, 2016, edition of Nature Communications, a multi-institutional team including nine Livermore researchers present spectrally resolved x-ray scattering measurements on dynamically compressed deuterium. Hydrogen, the most abundant element found in the universe, has applications to planetary science, inertial confinement fusion, and fundamental physics, and therefore, its high-pressure properties have been the subject of intense study. However, questions about hydrogen’s high-pressure phase diagram have remained unresolved.
The team determined deuterium’s ionization state as a function of pressure. The onset of ionization occurs at about three times compression, close in pressure to where density functional theory–molecular dynamics simulations predict molecular dissociation, suggesting that hydrogen transitions from a molecular and insulating fluid to a conducting state without passing through an intermediate atomic phase. This work is important to understanding the physics of the interiors of giant planets such as Jupiter, where details of hydrogen’s dissociation under pressure and its transition to electrical conductivity influence the processes that result in planetary magnetic fields. The research also advances implosion modeling at Livermore’s National Ignition Facility, where designers must understand the high-pressure properties of hydrogen in order to produce targets that enable progress toward fusion ignition. Livermore’s Laboratory Directed Research and Development program supported this research.
In a paper appearing in the April 12, 2016, issue of Physical Review B, a team of researchers from Lawrence Livermore and Sandia national laboratories present an absolute pressure–density relationship for elemental copper up to 450 gigapascals (GPa), extending the previous 250-GPa calibration. Copper is an important material for the engineering and academic communities and is often used at Sandia’s Z pulsed-power facility as an electrode for materials dynamics experiments, at Livermore’s National Ignition Facility (NIF) as an ablator, and within the diamond-anvil-cell community as a high-pressure standard.
Using the Z facility, the team leveraged magnetically driven uniaxial compression waves to compress thick copper samples to more than 450 GPa (approximately 4.4 million times surface atmospheric pressure). They determined the stress-density compression path from sound velocity measurements. In this paper, the team presents a method for correcting for the effects of strength and heating caused by plastic deformation. They show that their technique is inherently more accurate at high pressures than current methods. These results should provide the community of static high-pressure researchers with an easy-to-use pressure standard at extreme conditions. The National Nuclear Security Administration (NNSA) funds Sandia’s Z machine and Livermore’s NIF, two of NNSA’s experimental capabilities that are essential components of assessing nuclear performance issues as part of the stockpile stewardship program.
The Presidential Early Career Award for Science and Engineering (PECASE) is the highest honor bestowed by the U.S. government on science and engineering professionals in the early stages of their independent research careers. Lawrence Livermore astrophysicist Tammy Ma was selected for a PECASE award, one of 106 recipients nationwide and one of 13 from the Department of Energy. Ma was recognized for her “innovation and leadership in quantifying hydrodynamic instability mix in the hot spot of inertial confinement fusion implosions on the National Ignition Facility (NIF); key contributions to experiments demonstrating fusion fuel gains exceeding unity; and broad educational outreach and service to the scientific community.” In addition, former LLNL engineering postdoc Jonathan Hopkins was awarded a PECASE, largely for work he did as an LLNL postdoc. Hopkins is currently an assistant professor of mechanical engineering at the University of California, Los Angeles. After earning her Ph.D. from the University of California, San Diego, Ma completed a postdoc at LLNL before becoming a staff scientist in 2012, where she currently heads the X-Ray Analysis Group for the inertial confinement fusion (ICF) program.
Fundamental to Lawrence Livermore’s primary mission of ensuring the safety, security, and reliability of the nation’s nuclear stockpile is obtaining a better understanding of the shape, structure, stability, and behavior of atoms, particularly under extreme conditions. In an effort to find evidence of rare octupole deformation—pear-shaped atomic nuclei—an international team including Livermore postdoc Brian Bucher and scientist Ching-Yen Wu performed experiments on the Argonne Tandem Linac Accelerator System at Argonne National Laboratory. The accelerator generates high-intensity, high-energy beams to shed light on the structure of atomic nuclei. The team found evidence that the neutron-rich nuclei of Barium–144 are “squashed” or pear-shaped. In a March 18, 2016, paper in Physical Review Letters, first-author Bucher and the research team described their experiments. The team’s experimental results show the barium nuclei appear to be considerably more deformed than predicted by theory. Confirmation of these observations may require scientists to revise their current understanding of octupole deformation. Postdoc Bucher’s research is focused on the structure of how nuclei evolve with the addition or subtraction of individual nucleons; he is particularly interested in how nuclear structure influences astrophysical processes. The primary funding for the octupole deformation research was provided by the Department of Energy’s Office of Science.
For more than two decades, LLNL researchers have worked to understand and mitigate climate change. Quantifying how much heat is accumulating in the ocean is critical to understanding climate change because the ocean absorbs more than 90 percent of Earth’s excess heat associated with global warming. Livermore scientists, together with colleagues from the National Oceanic and Atmospheric Administration, Princeton University, and Pennsylvania State University, have found that half of the global ocean heat content increase since 1865 has occurred during the past two decades and that the warming is reaching deeper into the ocean. Livermore researcher Peter Gleckler was lead author of a paper published in the January 18, 2016 online journal Nature Climate Change. The paper detailed a study that combined a diverse set of historical observations together with current climate models to identify changes in the ocean greater than 700 meters depth. The analysis suggests that nearly half of the industrial-era increases in global ocean heat content have occurred in recent decades, with over a third of the accumulated heat occurring below 700 meters. The estimates of ocean warming are consistent with results from the latest generation of climate models. Livermore’s contribution to the study was funded by the Department of Energy’s Office of Science.
Livermore scientists have been among the leaders in adopting, advancing, and demonstrating the capabilities of additive manufacturing, also called three-dimensional (3D) printing. In this revolutionary process, objects are built up one ultra-thin layer at a time. Researchers from LLNL and the University of California Santa Cruz achieved an important milestone when they used a 3D printer to manufacture grapheme aerogel supercapacitors that are extremely stable and capable of nearly fully retaining their energy capacity even after 10,000 consecutive charging and discharging cycles. The results were released online in the journal Nano Letters on January 28, 2016. The experimenters used a 3D-printing process called direct-ink writing and an extrudable graphene-oxide composite ink designed at LLNL. Graphene-based inks feature ultrahigh surface area, lightweight properties, elasticity, and superior electrical conductivity. The novel LLNL graphene composite ink has an engineered porous (aerogel) architecture. The researchers predict that future 3D-printed supercapacitors may make possible new products that are currently difficult or impossible to manufacture using other methods. Examples include efficient energy storage systems for smartphones, wearables, implantable devices, electric cars, and wireless sensors. Livermore’s Laboratory Directed Research and Development program funded this work.
A major security concern is the threat of nation-states or terrorists obtaining radiological or nuclear materials for illicit purposes. To help address this threat, Lawrence Livermore researchers have applied their expertise in nuclear weapons and isotopes to the discipline of nuclear forensics. In this field, investigators analyze nuclear or radioactive materials for clues to a material’s source to identify where legal control was likely lost. In an article appearing on the cover of the February 2, 2016, issue of Analytical Chemistry, LLNL researchers Mike Kristo and Ruth Kips, in collaboration with colleagues at the Australian Nuclear Science and Technology Organization, described the current science of nuclear forensics, including work performed at Lawrence Livermore under several sponsors. The team cited examples of nuclear forensic signatures that allowed investigators to identity unknown nuclear material. Signatures describe material characteristics such as isotopic abundances, elemental concentrations, physical and chemical forms, and physical dimensions that can link a material to individuals, locations, or processes. There is currently no single nuclear forensic signature capable of identifying all unknown nuclear materials. This fact reflects the diverse materials that make up the nuclear fuel cycle, from natural materials such as uranium ores to highly processed materials such as nuclear fuels. Therefore, scientists must apply analytical techniques from several disciplines, including analytical chemistry, radiochemistry, and materials science.
Additive manufacturing, or three-dimensional (3D) printing, holds great promise as a way to tailor material behavior. In research illustrated on the cover of the March 9, 2016, issue of Advanced Materials, a team of Livermore and Harvard researchers demonstrated that 3D printing can be used to tailor the dynamic behavior of reactive materials, which produce controlled releases of energy, as in airbag initiation. The team created two different reactive material architectures—channels and hurdles, both composed of silver nanoparticle ink. The team used 3D printing to create conductive electrodes from the ink, and then used electrophoretic deposition to coat them with aluminum/copper oxide thermite films. The channel and hurdle architectures offered different orientations of the multiphase expansion event relative to the flame propagation direction. Observations revealed that the precise spacing and orientation of these architectures played an important role in manipulating the resultant energy transport, offering a pathway for tailoring the energy release rate apart from the conventional method of changing the mixing scale or formulation. The researchers suggest that controlling reactivity using architected design will lead to new types of materials for initiation systems, propellants, and pyrotechnics. This work was funded by the Laboratory Directed Research and Development Strategic Initiative Program.