By Neal Singer
It’s not immediately obvious why accelerating a projectile about the size of a stick of gum to 25 times the speed of a rifle bullet and smashing it into a target in central New Mexico would say anything about the state of diamonds on Neptune.
Or about efforts to produce nuclear fusion at Lawrence Livermore National Laboratory’s National Ignition Facility in California.
It does because the Sandia work — reported in the Dec. 19 issue of the journal Science — provides data 10 times more accurate than ever before achieved of the pressures needed to change diamond into a state of slush and then to a completely liquid state.
On the way, as a bonus to science and to the researchers — Marcus Knudson (1646), Mike Desjarlais (1640), and Daniel Dolan (1646) — a triple point was discovered at which solid diamond, liquid carbon, and a long-theorized but never before confirmed state of solid carbon called bc8 were found to exist together.
Accurate knowledge of these changes of state — changes similar to those undergone by ice as it melts into water, but under much more extreme conditions — are essential in simulating behaviors of celestial bodies.
On Neptune, for example, much of the atmosphere is composed of methane (CH4). Under high temperatures and pressures, methane decomposes, liberating its carbon. One question for astrophysicists in theorizing the planet’s characteristics is knowing the form that carbon takes in the planet’s interior. At what precise pressure does simple carbon form diamond? Is the pressure eventually great enough to liquefy the diamond, or form bc8, a solid that has yet other characteristics?
“Liquid carbon is electrically conductive at these pressures, which means it affects the generation of magnetic fields,” says Mike. “So, accurate knowledge of phases of carbon in planetary interiors makes a difference in computer models of the planet’s characteristics. Thus, better equations of state can help explain planetary magnetic fields that seem otherwise to have no reason to exist.”
At NIF in 2010, 192 laser beams are expected to focus on isotopes of hydrogen contained in a little spherical shell made of diamond. The idea is to bring enough heat and pressure to bear to evenly squeeze the shell, which serves as a containment capsule. The contraction is expected to fuse the nuclei of deuterium and tritium within.
The success of this reaction would give more information about the effects of a hydrogen bomb explosion, making it less likely the US would need to resume nuclear weapons tests. It could also be a step in learning how to produce a contained fusion reaction that could produce electrical energy for humanity from seawater, the most abundant material on Earth.
For the reaction to work, the spherical capsule must compress evenly. But at the enormous pressures needed, will the diamond turn to slush, liquid, or even to the solid bc8? A mixture of solid and liquid would create uneven pressures on the isotopes, thwarting the fusion reaction, which to be effective must offer deuterium and tritium nuclei no room to escape.
That problem can be avoided if researchers know at what pressure point diamond turns completely liquid. One laser blast could bring the diamond to the edge of its ability to remain solid, and a second could pressure the diamond wall enough that it would immediately become all liquid, avoiding the slushy solid-liquid state. Or a more powerful laser blast could cause the solid diamond to jump past the messy triple point, and past the liquid and solid bc8 mixture, to enter a totally liquid state. This would keep coherent the pressure on the nuclei being forced to fuse within.
The mixed-phase regions, says Dan, are good ones to avoid for fusion researchers. The Sandia work provides essentially a roadmap showing where those ruts in the fusion road lie.
Sandia researchers achieved these results by dovetailing theoretical simulations with laboratory work.
Simulation work led by Mike used density functional theory to establish the range of velocities at which projectiles, called flyer plates, should be sent to create the pressures needed to explore these high pressure phases of carbon and how the triple point would reveal itself in the shock velocities.
(Density functional theory is a powerful method for solving Schrödinger’s equation for hundreds to thousands of atoms using today’s large computers.)
Using these results as guides, experimental results from 15 flyer-plate flights — themselves powered by the extreme magnetic fields of Sandia’s Z machine — in work led by Marcus, then determined more exact change-of-state transition pressures than ever before determined. Even better, these pressures fell within the bounds set by theory, thus showing that the theory was accurate.
“These experiments are much more accurate than ones previously performed with laser beams,” says Marcus. “Our flyer plates, with precisely measured velocities, strike several large diamond samples, which enables very accurate shock wave velocity measurements.”
Laser beam results, he says, are less accurate because they shock only very small quantities of material, and must rely on an extra step to infer the shock pressure and density.
Sandia’s magnetically driven plates measure about 4 cm by 1.7 cm in cross section, are hundreds of microns thick, and impact three samples on each firing. Z’s target diamonds are each about 1.9 carats, while laser experiments use about 1/100 of a carat.
“No, they’re not gemstones,” says Mike about the Sandia targets.
The diamonds in fact are created through industrial processes and have no commercial value, says Dan, though their scientific value has been large. -- Neal Singer
Diamond-like carbon films created at Sandia are helping probe the far boundaries of the solar system as part of a NASA mission to study how the sun’s solar wind interacts with the interstellar medium — the matter that exists between the stars within a galaxy.
The films are in the low-energy sensor (IBEX-Lo) on board NASA’s Interstellar Boundary Explorer (IBEX), which lifted off in October on a mission to study the farthest fringes of the solar system. IBEX’s two bucket-sized sensors, covering high and low energy ranges, are designed to capture particles bouncing back toward Earth from the distant boundary between the hot wind from the sun and the cold wall of interstellar space.
The active conversion surface of the low-energy neutral atom detector is coated with Sandia’s diamond-like films created by Tom Friedmann (1112).
“The primary purpose of the diamond-like carbon films is to provide a surface that will efficiently ionize energetic neutral atoms,” Tom says, “so they can then be detected. Smooth surfaces are required so that the scattered particles can be efficiently collected. If the surface is rough, scattered particles are lost, decreasing efficiency. The diamond-like carbon films have an average surface roughness that is about one angstrom. This is less than the diameter of a carbon atom.”
To create the 30 films aboard the system, Tom used pulsed-laser deposition to deposit the films on the conversion surfaces. Carbon was used because it has relatively high conversion efficiency, low sputter yield, and is very smooth, he says. Single crystal diamond has the highest efficiency but is too expensive to grow over large areas and difficult to polish to the extremely low surface roughness needed. The diamond-like carbon films naturally grow smooth and require no polishing.
Tom says the project took about one and a half months to complete and he says he was pleased with the outcome. Now the IBEX team is awaiting the results from the mission.
The IBEX team received a shock when the satellite was initially activated. A high-voltage system failed in the low- energy sensor, and it was initially feared that the mission would be diminished by the loss of that sensor’s data. But the team found a workaround that enables successful IBEX-Lo operation after all and that will allow the mission to achieve most of its goals.
Eric Hertzberg, from Lockheed Martin Advanced Technology Center, approached Tom to create the films. Hertzberg is the lead engineer for the IBEX-Lo Sensor. Bob Nemanich, Arizona State University, also played a key role in passivating the films. Tom says Sandia uses similar films in studies of electron field emission and in microelectromechanical systems (MEMS) devices.
Voyager 1, launched in 1977, made the first direct measurements of this boundary (the heliopause) as it was the first spacecraft to leave the inner solar system and head toward interstellar space. Voyager 2, launched the same year, will also relay observations of the boundary — but these measurements are of only one place and time. IBEX is designed to provide a three-dimensional map of the boundary. — Michael Padilla
By Mike Janes
At a press conference in New York City on Feb. 10, General Motors and Sandia announced that biofuels made from plants, forestry waste, and dedicated energy crops could sustainably replace nearly a third of US gasoline usage by 2030. The announcement was made at the Biotechnology Industry Organization (BIO) CEO & Investor Conference.
Bob Carling, director of Transportation Energy Center 8300, presented the results of the GM-funded “90 Billion Gallon Biofuel Deployment Study.” The goal was to assess if and how a large volume of cellulosic biofuel could be sustainably produced, processed, and delivered assuming technical and scientific progress continues at expected rates. The study was conducted at Sandia and GM over a period of nine months.
“This wasn't just GM coming to us to ask us to do a study for them,” said Bob at the news conference, “but instead it was a teaming opportunity where we were able to collectively address a critical national need alongside our GM partners.”
Sandia and GM researchers examined the interdependencies of land, water, infrastructure, workforce, economic, technology, and environmental factors and assessed the feasibility, implications, limitations, and enablers of annually producing 90 billion gallons of ethanol — sufficient to replace more than 60 billion of the estimated 180 billion gallons of gasoline expected to be used annually by 2030. Ninety billion gallons a year exceeds DOE’s goal for ethanol production established in 2006.
“In this study, Sandia leveraged its systems analysis expertise to develop a framework for open and transparent decision making,” says Terry Michalske, director of Energy Innovation Initiatives Center 6100. “This approach will prove invaluable in supporting investment and policy decision making and in helping to monitor and assess progress going forward.”
The 90 Billion Gallon Study assumes that 75 billion gallons would be ethanol made from nonfood cellulosic feedstocks and 15 billion gallons from corn-based sources. The study examined four sources of biofuels: agricultural residue, such as corn stover and wheat straw; forest residue; dedicated energy crops, including switchgrass; and short-rotation woody crops, such as willow and poplar trees. It examines the costs of producing, harvesting, storing, and transporting these sources to newly built biorefineries.
Using a newly developed tool known as the Biofuels Deployment Model, or BDM, Sandia researchers determined that 21 billion gallons of cellulosic ethanol could be produced each year by 2022 without displacing current crops. The Renewable Fuels Standard, part of the 2007 Energy Independence and Security Act, calls for ramping up biofuels production to 36 billion gallons a year by 2022.
The 90 Billion Gallon Study, which focused only on starch-based and cellulosic ethanol, found that an increase to 90 billion gallons of ethanol could be sustainably achieved by 2030 within real-world economic and environmental parameters.
The industrial processes by which nonfood forms of biomass are converted into sugars suitable for production of biofuels were a focus of the study.
Sandia’s analysis also included land use, water availability, energy used to produce cellulosic biomass, transportation of feedstocks, and other potential leverage points for the development and use of cellulosic biofuels. In conducting its research, Sandia utilized models that examined current and future technologies for development of ethanol.
Future enhancements to Sandia’s BDM are planned, contingent on additional partnerships. Such improvements to the current software tool, says Carrie Burchard, from Business Development Support Dept. 8529, would provide an even more comprehensive systems understanding of the biofuels industry.
Sandia enjoys a longstanding relationship with all the major US automakers and engine manufacturers, and has worked previously with GM on a variety of automotive research activities. Sandia also plays a major role in the Joint BioEnergy Institute (JBEI) and several other transportation energy and biofuels projects.
An executive summary of the 90 Billion Gallon Biofuel Deployment Study can be found at www.hitectransportation.org.
Larry Burns, GM’s VP for Research & Development and Strategic Planning, in remarks at the news conference put the Sandia/GM work in real-world perspective: “If you really want to impact imported oil and move the needle quickly, there’s nothing more attractive than biofuels in the automotive sector.”