EXPLORATION of material behavior under extreme pressures and temperatures is one of the foundational scientific pillars that undergirds Lawrence Livermore’s national security mission work. Extreme conditions, for instance, inform our assessments of conventional and nuclear munitions design and performance and help us to analyze and refine inertial confinement fusion experiments at the National Ignition Facility (NIF). Furthermore, enhancing our understanding of Earth’s response to nuclear detonations supports treaty verification efforts, while knowledge of how airplanes and other human-made structures respond to extreme events helps us to better prepare for potential terrorism scenarios. The more we understand about the behavior of materials at high pressures and temperatures, the better we can accomplish our missions.
To understand material behavior in the regimes of interest, we often must re-create extreme conditions in the laboratory with experimental platforms that use energy sources such as high explosives, gas guns, lasers, and diamond anvil cells coupled with sophisticated diagnostics. Most of these tools are used for dynamic compression, or shock physics, experiments. This area of research explores the physical and chemical changes that occur when a material is subjected to high pressures generated by extreme shocks, as discussed in the feature article (see Smashing Science), Livermore is one of a select number of institutions worldwide with a major, leading-edge shock physics experimental program. Since its establishment in the 1960s, the program has attracted talented scientists and launched a wide range of national security and fundamental science research efforts. Shock physics at Livermore has also produced some notable scientific breakthroughs, including the first observation of hydrogen’s elusive metallic phase and, more recently, the determination of iron’s melting point in Earth’s core.
Compression research is made possible in large part by Livermore’s rich array of experimental platforms, diagnostics, and computational tools. However, these efforts owe their biggest debt to the people involved, including the technicians and engineers who design and fabricate targets for NIF, the Joint Actinide Shock Physics Experimental Research Facility (see S&TR, April/May 2013, The Shot Heard 'Round the Complex), and other platforms; the theorists and computer scientists who support modeling and predicting materials behavior; and the technicians and physicists who execute and analyze experiments, among many others. Our skilled and multidisciplinary teams have developed and applied tools and techniques such as designer diamond anvil cells (see S&TR, December 2004, Putting the Squeeze on Materials) and photonic Doppler velocimetry (see S&TR, October/November 2012, Ten Times More Data for Shock-Physics Experiments). Over the years, these capabilities have transformed how high-pressure and high-temperature science are done.
Given the knowledge of material behavior, experience, and experimental resources we have amassed, Livermore is well equipped to take on problems that in the past seemed virtually intractable. One ongoing challenge we face in conventional munitions is providing the Department of Defense with options for targeting enemy combatants without injuring or killing nearby civilians or our own troops. In recent years, we have successfully used the understanding of material responses under extreme conditions developed through compression experiments and our supreme modeling tools to design lower collateral damage weapons (see S&TR, March 2013, Advanced Engineering Delivers More Exact Weapons Performance). In the coming years, I expect we will form even more effective solutions to this and other difficult problems. We will be aided in our efforts by Laboratory expertise in areas such as additive manufacturing, which lets us modify material properties beyond what nature gives us, as we have done through alloying in the past but to a greater extent.
Increased collaboration will also benefit our shock physics investigations. For instance, Livermore’s newly formed Center for High Energy Density Science, headed by laser experimentalist Gilbert (“Rip”) Collins, will work to create national and international research collaborations across academia, national laboratories, and industry. High-energy-density science studies the nature of matter and radiation under extreme and typically shock-driven temperature and density conditions, and has applications that range from astrophysics to stockpile stewardship. The new center, in the short time since its creation in October, has already established memoranda of understanding with several University of California campuses.
The success of many Laboratory missions will continue to rely on and benefit from advancements in our understanding of material properties. The prospect of tailoring those properties through additive manufacturing opens the door to a whole new level of creativity and innovation—hallmarks instilled by our founders in the DNA of Livermore. Compression research at Livermore is a dynamic area, and the outlook for it is bright not only for those involved directly with the research but also for those who look to apply that advanced understanding to accomplish our national security missions.