The Laboratory in the News

Nation’s Renewable Energy Use on the Rise

Each year, the Laboratory releases flowcharts that track the nation’s consumption of energy resources. According to the most recent U.S. charts released, Americans used less coal and more natural gas, solar panels, and wind turbines to generate electricity in 2012.

“Natural gas use is up particularly in the electricity generation sector,” says A. J. Simon, a Livermore energy systems analyst. Sustained, low natural-gas prices have prompted a shift from coal to gas in this sector. According to Simon, the rise in renewables is tied to prices (the underlying cost of solar panels and wind turbines has gone down) and policy (government incentives to equipment installers as well as renewable energy targets in various states). Overall, Americans used 2.2 quadrillion British thermal units, or quads, less coal in 2012 than the previous year, while natural gas use jumped to 26 quads from 24.9 quads the previous year.

Once again, wind power saw the highest percentage gains, from 1.17 quads produced in 2011 to 1.36 quads in 2012. In response to government-sponsored incentives to invest in renewable energy, new wind farms continue to come online with larger, more efficient turbines than have been previously developed. Solar also jumped from 0.158 quads in 2011 to 0.235 quads in 2012. Extraordinary declines in the price of photovoltaic panels because of global oversupply drove this shift.

“This year is the first in at least a decade that we’ve seen a measurable decrease in nuclear energy,” says Simon. “The cut is likely permanent because four nuclear reactors recently went offline. A couple of nuclear plants are under construction, but they won’t come online for another few years.”

The majority of energy use in 2012 was for electricity generation (38.1 quads), followed by the transportation, industrial, residential, and commercial sectors. However, energy use in the residential, commercial, and transportation sectors decreased while industrial energy use increased slightly.

Record Pressure for Solid Iron Achieved

In a series of experimental campaigns led by Livermore’s Yuan Ping using the OMEGA laser at the University of Rochester’s Laboratory for Laser Energetics (LLE), researchers compressed iron up to 5.6 million atmospheres (5.6 million times the pressure at Earth’s surface), a record for solid iron. Iron is the most abundant element in Earth’s core and the sixth most abundant element in the universe. As a key component of terrestrial planets and exoplanets, it is one of the materials most often studied under extreme conditions.

The record pressure was achieved using multishock compression. A series of shocks (rather than a single shock) keeps the entropy low during material compression, which is key to maintaining the temperature lower than iron’s melting point and allowing it to remain solid. The team used an x-ray technique called EXAFS (extended x-ray absorption fine structure) to diagnose iron’s material properties under the extreme pressure. This effort resulted in the first EXAFS data in high-energy-density (HED) matter.

The data show that the close-packed structure of iron is stable in the regime explored, confirming simulation predictions and experimental studies using x-ray diffraction up to 3 million atmospheres. Unexpectedly, the team found that the temperature at peak compression is significantly higher than that from pure compressive work, and the dynamic strength of iron is many times greater than the static strength based on lower pressure data.

Ping says, “The measurement technique can now be scaled up to larger laser systems, such as the National Ignition Facility, to reach higher pressures or to study dynamics in HED materials.” The research was reported in August 9, 2013, issue of Physical Review Letters. The work was funded by the Laboratory Directed Research and Development Program and the Department of Energy’s HED Laboratory Plasmas Program. Livermore coauthors are Federica Coppari, Damien Hicks, Dayne Fratanduono, Sebastien Hamel, Jon Eggert, James Rygg, Raymond Smith, Damian Swift, David Braun, and Gilbert Collins. The team also includes two coauthors from LLE, Barukh Yaakobi and Tom Boehly.

Efficient Energy Harvesting Garners Journal Cover

Black metals could someday provide a pathway to more efficient photovoltaic solar cells to improve harvesting solar energy. A team of Livermore researchers led by engineer Tiziana Bond is experimenting with plasmonic black metals, which are nanostructured materials that have low reflectivity and high absorption rates of visible and infrared light. The nanopillar structures are trapping and absorbing sunlight. When black silicon, a semiconductor material, is roughened at the nanoscale level, it traps light by multiple reflections, increasing absorption to more efficiently trap the Sun’s wavelengths. Team member physicist Mihail Bora reported this study in the cover article of the June 24, 2013, issue of Applied Physics Letters.

The plasmonic substrate studied by the researchers is composed of a square array of vertically coupled nanowires coated with gold, silver, or aluminum. The team’s design is based on a cavity with multiple closely spaced resonances to form an oscillating system. The excitation end of the cavity is engineered to form an ultrasharp groove that broadens the plasmonic resonances and dissipates most of the incident energy into the metal, thus creating higher absorption rates.

The team’s experiments have increased the average absorbance of the substrates to more than 75 percent above the visible range (400 to 800 nanometers). This achievement is remarkable considering all three metals are used to fabricate highly reflective optical mirrors. According to Bora, the significance of aluminum nanostructures for large-scale applications is underscored by the fact that aluminum is the least expensive pure metal and the third most abundant element in Earth’s crust after oxygen and silicon. Coauthors include Elaine Behymer, Allan Chang, Keiko Munechika (now at Lawrence Berkeley National Laboratory), Dietrich Dehlinger (now at Illumina, Inc.), Cindy Larson, Hoang Nguyen, and Jerald Britten.

Meteorite Mineral Named for Livermore Cosmochemist

A mineral discovered in a refractory inclusion of the Allende meteorite has been named in honor of Livermore cosmochemist Ian Hutcheon, who has made numerous contributions to the study of meteorites and what they reveal about the evolution of the early solar system. The discovery of the mineral by Sasha Krot from the University of Hawaii and Chi Ma from the California Institute of Technology was formally announced at the annual meeting of the Meteoritical Society in Edmonton, Canada, this past summer. The hutcheonite mineral structure and name have been officially approved by the International Mineralogical Association.

Refractory inclusions within meteorites are the oldest objects in the solar system. Hutcheon has been studying these, specifically in the meteorite Allende, since the 1970s, when he was a postdoctoral researcher at the University of Chicago. Allende is the largest carbonaceous chondrite meteorite ever found on Earth. It fell to the ground in 1969 over the Mexican state of Chihuahua and is notable for possessing abundant inclusions.

Hutcheon says, “I’m not in the business of discovering minerals, but I am interested in dating when these minerals formed and what happened to them several million years after they formed.” Hutcheon is also interested in determining when water formed on the asteroid from which Allende and other carbonaceous chondrite meteorites originated. By looking at the concentrations of elements and isotopes in minerals found in the Allende inclusions, Hutcheon and his team can trace how water got there and ultimately how water developed in the early solar system. Hutcheonite, which is clear with a tinge of blue, is less than one-tenth the width of a human hair and can be seen only with high-powered scanning electron microscopes.

Journal Cover Features Plutonium Cluster Study

Laboratory researchers Jim Tobin, Sung Woo Yu, and Brandon Chung, along with collaborators from the Russian Academy of Sciences and the E. I. Zababakhin Institute of Technical Physics, have developed a new approach to calculating the electronic structure of atomic clusters, specifically plutonium atom clusters. Their research appeared on the cover of the August 15, 2013, issue of International Journal of Quantum Chemistry.

For years, scientists have grappled with understanding how electronic structure changes as a function of the number of atoms in a cluster. “It has become clear over the past decade that an important mechanism for the long-distance transport of plutonium in groundwater is via suspended plutonium clusters or colloids,” says Tobin. “The electronic structure of such clusters controls their reactivity with mineral surfaces and hence their transport characteristics.”

The team’s research combines theoretical results with spectroscopic data, confirming the validity of the approach. Many groups have worked toward understanding the electronic structure of solids as a function of system size. Progress on actinide-containing materials has been slowed by experimental limitations related to the highly radioactive and chemically toxic nature of these materials and by theoretical difficulties of correlated electron systems characteristic of high-atomic-number elements.