Focus on APS Topical Groups

Compression of Condensed Matter

Editor’s Note: This article is the first in an occasional series that will highlight the activities of APS’s ten topical groups, units that may be small in numbers but that are often the locus of cutting-edge research.

Shock compression of condensed matter, the study of the response of materials to rapid compression through the use of explosive, laser, magnetic, and gas gun drivers, is a dynamic field, and the APS topical group on shock compression of condensed matter (GSCCM) is helping its members keep up with the latest developments. GSCCM was founded in 1984 to promote the development and exchange of information regarding the dynamic high-pressure properties of materials, shock physics, and detonation physics research.

Shock compression physicists study the behavior of materials undergoing rapid compression, most often in the form of a shock wave propagating through the material. Impact creates a state where there is high pressure and often high temperature behind the propagating wave. Shock physicists then use velocimetry, spectroscopy, and diffraction techniques to analyze the response of the material, looking for phase transformations, chemical reactions (in the case of explosives), and the dynamic strength of the material.

These techniques are useful for understanding and developing armor for military use and for developing new defense mechanisms against attackers. They also contribute fundamental knowledge that can be used in the aerospace and automotive industries for many applications.

Because of the military applications of the field, many shock physicists work for national labs and/or are part of the defense community, said David Funk, current chair of the GSCCM.

In addition to the applications, shock physics has fundamental interest, said Funk. Scientists use shock techniques to understand a wide variety of materials’ properties. For instance, shock techniques are useful in the study of Earth and other planetary materials, because they can be used to generate extreme high temperature and pressure conditions such as those that might be found in giant planetary interiors.

Recently, increases in computing power have made it possible to simulate materials at the atomic level. Simulations can be done with up to several billion atoms. Previously, shock scientists had only been able to study materials at a composite level, but now they can use simulations to begin to connect what is happening at the atomic level with how it gives rise to the bulk properties of the material. This has opened up new opportunities, said Funk. “There’s still a lot of discovery science.”

With 367 members in 2007, GSCCM is one of the smaller topical groups. GSCCM helps its members stay connected and up to date on their field through biennial topical conferences on shock compression. This year’s meeting, which took place June 24-29 in Hawaii, attracted about 430 attendees.

The meeting included special sessions on shock waves in medical devices, isentropic compression of materials, and a town hall meeting on future directions in dynamic high pressure research.  Other topics included inelastic deformation, first-principles and molecular dynamics calculations, explosives and reactive materials, geophysics and planetary physics, optical spectroscopy and multiscale and continuum modeling. 

A number of recent developments were reported at the meeting. For instance, graduate student Cindy Bolme of MIT and Los Alamos described a new technique that uses femtosecond laser-driven shock waves that produce a wide range of pressures to determine the complete shock equation of state, not over the weeks or months usually needed, but on a single laser shot lasting just 300 picoseconds. Marcus Knudson of Sandia National Lab described using the Sandia Z-machine to study the shock melting properties of diamond. William Nellis of Harvard explained how several common and ordinarily soft materials, when compressed to pressures over one million atmospheres, become far stiffer than diamonds.

The topical group also presented the biennial Shock Compression Science Award, which this year was given to Dennis Grady of Applied Research Associates (Sandia National Laboratories retiree).

The topical group has recently launched a quarterly newsletter that contains information on upcoming conferences, news of award winners, job announcements, obituaries, and other items of interest to the topical group. The newsletter should help to keep the community involved, said Funk.

The topical group has also been working to hold dedicated sessions at the APS March Meeting. In recent years GSCCM attendance at the March Meeting has been about 45-50 people; the topical group would like to increase that to about 80. At this year’s March Meeting, the interests of GSCCM were represented at a focus session on Earth and planetary materials. GSCCM vice-Chair Marcus Knudson is leading the effort to plan sessions that will help to ensure strong GSCCM participation at the 2008 March Meeting in New Orleans.