DOE Laboratory Practicum

The Nevada National Security Site (NNSS) is a research laboratory complex larger than the state of Rhode Island that serves as the nation’s premier facility for high-hazard experimentation in support of the National Nuclear Security Administration’s Stockpile Stewardship and Global Security missions. Complementing our extensive experimental program are computational efforts in support of experimentation, including multiphysics and radiation transport modeling and simulation, modeling of radiation detectors and other instrumentation, and algorithms development for data analysis and uncertainty quantification.

Plasma Physics Modeling

Among the highest priority missions in Stockpile Stewardship experimentation at the NNSS is development of nuclear fusion reactors, used as pulsed neutron sources. The development of a next-generation Dense Plasma Focus (DPF) requires both particle-in-cell and magnetohydrodynamic modeling and simulation to characterize deuterium and tritium gas ionization, plasma sheath development, and the formation of the Z-pinches that result in beam-target fusion reactions on short time and length scales. Our current modeling and simulation efforts are performed using the Large-Scale Plasma (LSP) code and its variants. Projects in this area will allow DOE CSGF recipients to have direct and immediate impacts on the next generation of subcritical nuclear experiments at the NNSS and provide opportunities to collaborate with other modelers as well as experimentalists.

Algorithms Development for Uncertainty Quantification in Large-scale Data Analysis

One of the core experimental programs at the NNSS is the subcritical experiments program (SCE), which provides data characterizing the implosion hydrodynamic behavior of plutonium and surrogate materials. A wide range of data is collected, including interferometric velocimetry, interferometric position measurements, and X-ray radiography, among others. Each of these measurements requires mathematical models to characterize the physics of the detection systems, as well as statistical algorithms for inferring information from the data and quantifying the associated uncertainties. The NNSS data analysis team is active in the research and development of hierarchical Bayesian models for inverse problems associated with large-scale data, as well as Markov Chain Monte Carlo methods for sampling from Bayesian posteriors. Projects in this focus area will include collaborations with diagnosticians who are developing the latest measurement systems for material studies in extreme temperatures and pressures, and will require the development of entirely new computer codes.

Radiation Transport Modeling

When designing and fielding measurement systems for controlled experiments, or in real-world environments, it is essential to fully characterize the diagnostics. In both Stockpile Stewardship and Global Security radiation detection applications, this involves modeling and simulation of the radiation transport. NNSS scientists use Monte Carlo codes to simulate radiation transport in a wide range of scenarios, from characterizing how the X-rays generated by a brehmstrahlung source transport through a laboratory to how detectors will respond to emissions from radioactive sources. Projects in this focus area will include learning and using the Monte Carlo N-Particle (MCNP) radiation transport code.