Lawrence Livermore National Laboratory

The overwhelming majority of the yield from a nuclear weapon is produced in the high-energy-density (HED) state with temperatures and pressures similar to those of the sun. Livermore's Inertial Confinement Fusion (ICF) program aims to understand these regimes to ensure the current and future nuclear stockpile is safe and reliable.

Inertial Confinement Fusion

An ICF ignition target consists of a tiny metallic case called a hohlraum that holds a capsule filled with deuterium–tritium fuel. Within 20 billionths of a second, the capsule is compressed and heated to create the conditions similar to those of the sun.

The ICF program supports the Stockpile Stewardship Program by designing and fielding experimentally diagnosable platforms that access extreme temperature, pressure, and density regimes relevant to nuclear weapons. Igniting deuterium–tritium (DT) fuel for the first time in the laboratory is a particularly important effort.

Our experimental program provides an avenue for scientists and engineers to test their ideas and skills in a highly integrated and challenging environment for high-energy-density science.

This program is a critical component in developing and validating state-of-the-art high-energy-density models and simulation codes. Our experimental program provides an avenue for scientists and engineers to test their ideas and skills in a highly integrated and challenging environment for high-energy-density science while providing the opportunity to focus on specific physics issues when needed.

The ICF effort has the grand challenge of achieving fusion “ignition” with multi-megajoule fusion yields and, ultimately, a high-yield platform. Ignition occurs when the energy produced by nuclear fusion reactions exceeds the energy supplied.

Laser Indirect Drive

The main approach to ignition explored at LLNL's National Ignition Facility (NIF) is called laser indirect drive. Using a DT capsule inside a small gold target called a hohlraum, NIF’s 192-laser array heats the hohlraum generating x rays that compress the capsule forming a “hot spot” surrounded by a dense fuel layer. If successful, the burn propagates through the fuel too quickly for the capsule to expand, thus confining the fusion reaction within its own mass. Under laboratory conditions, this ICF reaction lasts much less than a billionth of a second.

In the laser indirect drive approach, laser light enters the hohlraum and deposits its energy in the gold wall generating x rays that compress the DT-filled capsule at the center of the hohlraum.

Challenges Abound in HED Science

Mastering ICF requires understanding of implosion physics, thermonuclear reactions, and radiation transport. Through sustained experimental effort, we have increased hot-spot pressures to groundbreaking levels that are within a factor of two required for ignition. Pitting state-of-the-art computer simulations of ICF implosions against x-ray and nuclear diagnostic data is a critical component in advancing our understanding.

State-of-the-art 3D computer modeling improves our understanding of the state of the compressed fuel near peak neutron production.

We are building the future of ICF research by continually pushing the boundaries of computer models, high-fidelity diagnostic techniques, and advanced data analysis. To achieve ignition, our team uses capabilities in the following areas to identify obstacles and seek innovative solutions:

  • Radiation hydrodynamics
  • Laser–plasma interactions
  • Implosion physics
  • Thermonuclear burn
  • Fundamental physical properties
    • Atomic physics
    • Equation of state

Under the direction of the U.S. Department of Energy/National Nuclear Security Administration, LLNL pursues ICF research with Los Alamos National Laboratory, Sandia National Laboratory, and the University of Rochester’s Laboratory for Laser Energetics. With HED science as a core competency, our efforts continue to strengthen the foundation of stockpile stewardship.