Weapon Physics and Design

 The safety, security, and effectiveness of the stockpile are at the core of the U.S. deterrence policy, and the Weapon Physics and Design (WPD) Program is responsible for ensuring its enduring credibility without nuclear testing.

Sierra High Performance computer
World-class computational and experimental facilities – like the Sierra High Performance computer (left) and the National Ignition Facility (right) – allow our physicists to model, simulate and validate complex models of high-energy-density NIF experiments (inset), which are crucial to ensuring a credible nuclear deterrent without full-scale testing.


Our scientists complete this critical mission by developing and applying validated, science-based capabilities in support of the current and future U.S. nuclear stockpile through the Stockpile Stewardship Program (SSP)Our multidisciplinary teams are assessing a stockpile that is older than any tested during the underground testing era, while modernizing the physics package of two warheads for deployment on new delivery systems. To do this complex work, we perform applied physics research, developing new models to advance physical and computational sciences relevant to national security missions, and the nuclear stockpile in particular. We design, field, and analyze experiments leveraging world-class research facilities at LLNL and across the National Nuclear Security Administration (NNSA) complex to help validate these models.

To ensure we can provide the stockpile science capabilities the nation counts on, we aggressively pursue preeminence in high-performance computing, high-energy-density (HED) science, next-generation experimental technologies, energetic materials, and advanced manufacturing.

  • Computing: We make use of some of the world’s most powerful high-performance computing capabilities on a daily basis, modeling and simulating complex multi-dimensional physical system relevant to the stockpile. LLNL truly is a world leader in computing, and our physicists are the primary users of those machines and codes. In order to overcome fundamental limitations on platform peak speeds, we are also leveraging advances in machine learning (ML), artificial intelligence (AI) and cognitive simulation to create a force multiplier for our experimental and weapon designers.

  • HED science: 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. To improve our understanding of these extreme temperature, pressure, and density regimes, we design and field experimentally diagnosable platforms on the world’s most powerful laser system, the National Ignition Facility (NIF). These HED experiments provide a keystone stockpile science capability that informs judgements of the current and future stockpile. These HED experiments also are key to our pursuit of the grand challenge of achieving inertial confinement fusion (ICF) “ignition” with multi-megajoule fusion yields and, ultimately, a high-yield experimental platform. With such a platform, we would be able to access the most extreme conditions in a nuclear detonation in a laboratory setting.

  • Next-generation experimental technologies: We rely on experiments and legacy data from the nuclear test history to validate complex multi-dimensional simulations in support of stockpile stewardship. As the legacy stockpile ages and we are asked to refurbish and modernize systems, we are challenged to assess and certify systems increasingly distant from the nuclear test history. To tackle this challenge, we are developing novel experimental platforms, targets, drivers and diagnostics. Our efforts in this area emphasize new technology options for a high fusion yield facility, advanced radiography concepts using both lasers and pulsed power, and advanced HED capabilities to support emerging needs in survivability, and modern manufacturing.

  • Energetic materials: We help play an important role in ensuring the high explosives (HE) that drive nuclear detonations remain safe and reliable far into the future. Applied HE research at LLNL aims to establish a predictive understanding of the fundamental physics of energetic materials through modeling, simulation, and experimentation – both scaled focused tests and integrated hydrodynamic experiments. In the end, this fundamental physics understanding informs our assessments, which are used to certify that HE in the stockpile will perform as expected.

  • Advanced manufacturing: Refurbishing and modernizing aged systems requires manufacturing components that may not have been made for more than a quarter century. We are partnering closely with engineers at LLNL and production plants across the country – including Kansas City National Security Complex (KCNSC)Y12 National Security Complex, the Pantex PlantLos Alamos National Laboratory, and the Savanna River Site – to lead a revitalization of the nation’s ability to manufacture nuclear weapon components. As we refurbish aged warheads, some materials and processes used when the weapons were made simply aren’t available anymore. We approach this challenge by designing with manufacturability in mind, and by conducting computational and experimental research aimed at ensuring processes can be qualified to produce reliable parts and materials and components will perform reliably and safely when they enter the stockpile.

World-class capabilities

WPD scientists leverage world-class facilities at LLNL and across the NNSA and Department of Energy (DOE) complex. We conduct HED experiments at LLNL’s National Ignition Facility (NIF), Joint Actinide Shock Physics Experimental Research Facility (JASPER) at the Nevada National Security Site and other facilities around the complex like the Z-machine at Sandia National Laboratory and the Omega laser at the University of Rochester. In the area of high-explosives research and development, we make integrated use of LLNL's High Explosives Applications Facility (HEAF) and the explosives fabrication capabilities at Site 300. In support of the National Hydrodynamic Testing Program, scientists extensively use the complementary capabilities of the Dual-Axis Radiographic Hydrotest Facility (DARHT) at Los Alamos National Laboratory, LLNL’s Contained Firing Facility (CFF) at Site 300, and the U1a Complex at the Nevada National Security Site.

These experiments deliver experimental data for multi-dimensional simulations we conduct on some of the fastest high-performance computers in the world, including Sierrawhich clocks in at peak of 125-petaFLOP. In addition to Sierra, LLNL is home to three other machines on the 2020 Top500 list and is expanding its computing facilities to accommodate what is anticipated will be the world’s first exascale computer. This interplay between modeling, simulation and experimental validation serves as the fundamental basis of our approach to science-based stockpile stewardship.

Diverse backgrounds

Diversity – in all its dimensions – is essential to our strong and vibrant intellectual environment and critical to our ability to innovate. Building an inclusive culture, where each of us can contribute to our fullest ability, is the means by which we get the maximum benefit from everyone’s ideas, unique perspectives, and experiences. Our commitment to diversity and inclusion also incorporates consideration of academic background and discipline. Our scientists hail from universities around the country, bringing a diverse range of academic training and experiences. We all bring different experiences and expertise to the table – something we consider a core strength – and we all share a passion for scientific inquiry and a love of country.

Areas of scientific inquiry within WPD include:

  • Actinide properties

  • Atomic physics

  • Nuclear and thermonuclear physics

  • Computational physics

  • Diagnostics

  • Fluid dynamics and turbulence

  • Hydrodynamic experiments

  • HED physics and experiments

  • Material properties under extreme conditions

  • Nuclear safety and security

  • Plasma physics

  • Radiation and particle transport

  • Reactive flows and high explosives

  • Uncertainty quantification (UQ) and novel statistical methods

  • Radiation hydrodynamics

  • Laser–plasma interactions

  • Implosion physics

  • Thermonuclear burn