Nuclear Security

Can Exascale Computing Help Us Understand Extreme Materials?

Some things are difficult to understand—higher math, relationships, the appeal of reality TV—whereas other things are understood to be difficult—brain surgery, two-year olds, learning to speak Finnish. Then there’s the response of a material hit by a shock wave, which is not only difficult to understand, but trying to simulate it, even using the world’s most powerful computers, is sufficiently difficult that it currently can’t be done.

A shock wave is an extremely energetic disturbance that moves through matter at supersonic speeds. Like a flash flood tearing through a slot canyon, it arrives without warning. Matter suddenly finds itself immersed in the wild pressure and temperature maelstrom that trails the wall-like shock front. As the shock propagates through, say, a solid, it generates enormous mechanical stresses that can deform, crack, even shatter the material. Even if there is no structural damage, will the material properties be the same as they were before?

Read more: Understanding Extreme Materials

Plutonium is the most complex element in the periodic table, yet it is also one of the most poorly understood ones. But now a well-known scientific technique, nuclear magnetic resonance (NMR) spectroscopy, may turn out to be the perfect tool for uncovering some of plutonium’s mysteries.

Scientists at Los Alamos National Laboratory (LANL) and the Japan Atomic Energy Agency (JAEA) have detected the faint signal of plutonium-239’s unique nuclear magnetic resonance signature. This signal promises to become a Rosetta stone for deciphering the complex atomic-scale electronic properties of this perplexing element. Their paper on the subject, "Observation of 239Pu Nuclear Magnetic Resonance," was published in the May 18 issue of Science magazine."

Read more: Plutonium Less Mysterious Now

Physicists at Lawrence Livermore National Laboratory developed the grating-actuated transient optical recorder (GATOR), which won an R&D 100 Award. This optical instrument is designed to capture and record fleeting, sequential images of x rays and other radiation emitted from the miniature “stars” created in the National Ignition Facility target chamber. This work was derived from LDRD investigator Bruce Remington's project “From Super-Earths to Nucleosynthesis: Probing Extreme High-Energy-Density States of Matter with X-Rays."

Read more: High-Speed Imager for Fast Events

Researchers at Lawrence Livermore National Laboratory are developing a suite of tiny, rugged sensors that could be embedded inside every nuclear weapon to report on the health of critical components as well as on the external environment. The embedded sensors would relay information, perhaps through a USB-like port, whenever scientists deem it necessary. The sensors would thus make possible for the first time “persistent surveillance,” that is, continuous monitoring of a weapon’s state of health. Livermore’s Laboratory Directed Research and Development Program funded much of the original proof-of-principle research through the “Transformational Materials Initiative” (06-SI-005).

Read more: Enhancing Nuclear Stockpile Confidence

From its beginning, Sandia’s LDRD program has supported development of microelectromechanical system (MEMS) technologies, each MEMS a very small, selfcontained device integrating electrical and mechanical components that detect a change and respond with a micromechanical or micro-electrical control that has consequences in the macroscopic world. For example, imagine that you drop your laptop computer. Before it hits the ground, it has automatically shut down its hard drive: a MEMS inertial sensor that detects its acceleration toward the floor has responded with a shut-down control signal so that the read-write heads don’t crash down on the hard drive’s spinning platters.

Read more: MEMS Technologies

After toiling in the Boston-area world of high-technology, this Sandia LDRD PI perceived the need for greater intellectual challenge in his life, and it initially appeared that it would be the academic world from which that challenge would come. And so, in 1997, when the offer of a faculty position came from the University of New Mexico’s Mechanical Engineering Department, he decided that life had presented him with a rare opportunity, that is, to test the actual parameters of a vision.

Read more: Measuring Mesoscale Weapons Components

Pulsed power machines rely on gas breakdown phenomena. High-power gas breakdown switches are critical components in the ZR upgrade of the Z machine, for example, and will likely play roles in future larger power drivers. Gas switches rely on high-density electronegative gases and insulator barriers, which are often weak links in the lifetime of the components and are the most-common sources of failure in these machines. This project is attempting to secure a more fundamental understanding of how discharges interact with surfaces in dense electronegative gases from both modeling and experimental perspectives.

Read more: Understanding Surface Breakdown

Significant Advances Through New Materials

The Transformational Materials Initiative (TMI) developed new materials to transform stockpile surveillance—sensors to detect changes in stockpile weapons, more robust and less expensive weapon materials, and reformulated high explosives to make weapons inherently safer. These results will achieve significant immediate and long-term cost savings for the nuclear weapons complex.

Read more: Transformational Materials

Understanding the complex processes present in hot, dense radiative plasmas—mixtures of fast-moving gas and subatomic particles in nuclear decay—is vital to problems as varied as nuclear fusion energy and the physics of stars. The study of high-energy-density plasmas requires an understanding of matter at extreme conditions with pressures in excess of 1 megabar. This LDRD project targets hot, dense radiative plasmas incorporating intense levels of nuclear reactions. These plasmas have temperatures of a few hundred electronvolts to tens of kiloelectronvolts and densities of tens to hundreds of grams per cubic centimeters. The high temperature and density of these plasmas means there is a complex interplay of atomic, radiative, and thermonuclear processes that needs to be accurately described.

Read more: Understanding Radiative Plasmas