The Quality of Science and Engineering at the NNSA National Security Laboratories by unknow

Author:unknow
Language: eng
Format: epub
Publisher: The National Academies Press
Published: 2013-08-24T00:00:00+00:00

CONDENSED MATTER/MATERIALS SCIENCE AT EXTREME CONDITIONS

An in-depth understanding of how materials behave under extreme dynamic loading (very large compressions, high temperatures, large deformations, and short timescales) is at the core of the S&E base for the weapons program and is important for related national security missions at the laboratories. The intellectual vitality and excellence of the S&E that provides this understanding is essential to the health of the Stockpile Stewardship Program (SSP), non-proliferation and threat reduction, and applications related to conventional munitions. Although dynamic loading is of primary interest to the SSP, static high-pressure/high-temperature studies add considerable value to broader scientific and programmatic objectives. Within the umbrella of dynamic compression science, the focus is on condensed matter at extreme conditions (CMEC). Broadly speaking, CMEC involves thermo-mechanical loading of a material that is initially in a condensed-matter state. Depending on the specifics of the thermo-mechanical loading, the end state can be either a condensed-matter state, warm dense matter, or a dense non-ideal plasma. This section is focused only on those loading conditions where the resulting final state is also a condensed-matter state.

All three laboratories are engaged in CMEC activities, but there are significant variations in the levels of effort and the scientific emphasis at each. In a large measure, the majority of the scientific activities at each laboratory reflect the favored experimental platform of that laboratory to produce dynamic compression in materials: lasers at LLNL, explosives and high-velocity impacts at LANL, and pulsed power at SNL. Although each experimental platform creates significant benefits (and unique attributes) for CMEC efforts, each platform also has associated limitations. However, the coordination and prioritization of CMEC activities across the different platforms was not clearly defined.

Some noteworthy CMEC achievements in recent years are shockless (or ramp) compression at hundreds of gigapascals (using pulsed power and laser platforms) to produce thermodynamic states that were previously inaccessible; significant advances in multiscale-theory and computations to examine a broad range of condensed matter phenomena; effects of pulse shape and loading path on dynamic fracture; and advances in static pressure research through synchrotron measurements. Each of these achievements, scientifically noteworthy, also provides significant benefits for NW programmatic objectives.

Looking first at LLNL, the committee observed that scientific achievements in multiscale-theory and computations for a wide range of materials, including high explosives, are impressive and represent a longstanding strength at LLNL—that is, the lab’s ability to integrate theoretical advances at different length scales with continuing advances in hardware and software to benefit both scientific and programmatic activities. Lasers achieve shockless compression of materials to peak stresses of several terapascals, achieving condensed-matter states previously unattainable. This development opens up a new field—cold dense matter science. The static high-pressure, high-temperature research activities at LLNL are likely the strongest among the NNSA laboratories, and synchrotron measurements have been used very effectively for both scientific and programmatic needs. The combination of static pressure and laser-shock capabilities has been creatively used to study light elements and their mixtures. Overall, the scientific productivity, as measured by publications and professional recognition, is excellent, and the transition of scientific results to mission needs is commendable.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.