Studying matter under extreme conditions

High-energy-density (HED) science is the study of matter under extreme pressure and temperature. Matter subject to these conditions exhibits a wide range of interesting and often unpredictable behavior that transforms atomic bonds and material structures, creating complex chemical reactions, highly ionized materials, and plasmas. HED science exemplifies the dual-purpose research we conduct at Lawrence Livermore—working to support both our core nuclear weapons research and the fundamental science explorations that underpin our mission-focused work.

Today, HED science is a growing research discipline at the Laboratory. It has proven essential to modeling nuclear weapons, advancing the pursuit of controlled fusion energy, and understanding the composition and dynamics of planets and stars. An increasingly multidisciplinary field, HED leverages Livermore strengths in high-performance computing (HPC), materials science, chemistry, physics, and engineering.

A major focus of HED experiments is determining a material’s equation of state (EOS), or the relationship between pressure, temperature, and density. As described in a recent Science & Technology Review magazine article, “Gently Compressing Materials to Record Levels,” a useful technique for obtaining an EOS is ramp (or quasi-isentropic) compression. In this technique, refined over the past decade with important contributions from Livermore researchers, a material is pressurized “gradually,” over small fractions of a second. As a result, heating is limited to lower temperatures, maintaining a solid crystalline state at higher pressures. In contrast, a standard, nearly instantaneous shock raises temperatures significantly, melting or even ionizing a sample under investigation and limiting the study of its properties.

The 192-beam National Ignition Facility (NIF), the largest and most energetic laser in the world, is superbly equipped for conducting ramp compression experiments. NIF routinely creates temperatures and pressures similar to those that exist in the interiors of stars, the cores of planets inside and outside our solar system, and detonating nuclear weapons. The laser’s high energy and power, pulse shape control, and state-of-the-art diagnostics make NIF the premier facility for ramp compression at pressures measured in terapascals (10 million times Earth’s ambient air pressure).

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