Lawrence Livermore National Laboratory

LLNL’s Terascale Simulation Facility houses the Department of Energy Advanced Scientific Computing (ASC) Program’s Purple supercomputer, a 100-teraops (trillion operations per second) machine that is one of the fastest in the world. ASC Purple enables 3D simulations with high-fidelity physics models of the performance of a full nuclear weapon system.

NIF can create conditions—temperatures of 100 million degrees and pressures 100 billion times that of the Earth’s atmosphere—similar to those in stars and nuclear weapons. NIF is thus a cornerstone of the experimental element of stockpile stewardship.

The nuclear weapons in the U.S. stockpile range in age from more than 20 years to more than 40 years. The National Nuclear Security Administration’s Stockpile Stewardship Program (SSP) maintains the reliability and safety of the U.S. nuclear deterrent without the need for full-scale testing. The SSP is an ongoing process of surveillance, assessment, refurbishment, and reassessment.

NIF experiments are an essential component of the nation’s stockpile assessment and certification strategy because NIF provides the only process for scientists to gain access to and examine thermonuclear burn. These experiments also will help the nation maintain the skills of nuclear weapon scientists, which is crucial in order to assess the age-related changes that could compromise weapon reliability.

NIF allows researchers to perform experiments in a controlled environment and at a much higher rate than could have been imagined with underground testing. A problem can be picked apart and individual physics pieces can be studied. Researchers no longer have to wait for a supernova event to gather data or attempt to parse information from an underground test with limited diagnostics. Radiation transport also is central to the operation of nuclear weapons. With NIF, researchers can perform detailed radiation-hydrodynamic experiments.

Data from NIF experiments complement testing at other experimental facilities at Livermore and elsewhere. These data help inform and validate sophisticated, three-dimensional weapon simulation computer codes and bring about a fuller understanding of important weapon physics. In effect, NIF allows scientists to separate the pieces of the physics of a nuclear weapon and examine each piece in isolation.

Under Pressure

NIF beams also can be used to create conditions of extremely high energy density in materials. One example is using various arrangements of beams to shock materials and demonstrate how they behave at high temperatures and pressures. Understanding how the many different kinds of materials used in nuclear weapons behave, especially as they age beyond their intended lifetimes, under the extreme environments produced in a thermonuclear reaction is key.

NIF will be used to help address planned and proposed Stockpile Life-Extension programs, which are regularly planned refurbishments of weapon systems to ensure their long-term safety and reliability. Changes to weapon systems for safety and security can have unintended consequences if those changes cannot be fully validated. Full validation is achieved through the combination of experiments using facilities such as NIF and advanced computational modeling.