Advancement of Hybrid Fluid-Kinetic Modeling Efforts for High-Energy-Density–Physics
and Inertial Confinement Fusion Science

December 2017

Adam Sefkow, Assistant Professor of Mechanical Engineering and Physics at the University of Rochester and senior scientist at the University's Laboratory for Laser Energetics (LLE), compares his research in high-energy-density physics (HEDP) and inertial confinement fusion (ICF) to that of a detective determined to solve an enigma. He builds on the achievements of other scientists; interprets data learned from experiments at LLE, Lawrence Livermore National Laboratory, and Sandia National Laboratories; and recognizes how often something significant can be learned from unexpected results. The recipient of both an Early Career Research Program award from the U.S. Department of Energy and the 2017 Excellence in Fusion Engineering Award from the Fusion Power Associates, Sefkow is currently developing a hybrid fluid-kinetic multiphysics simulation code named CHIMERA.

CHIMERA has as its long-term goal the development of a state-of-the-art tool for HEDP and ICF scientists. Sefkow explains that "while progress has been made toward the development of robust and reliable models with predictive capability, more work remains to be done. Electromagnetic and kinetic particle-based approaches to modeling include many of the physics effects neglected within the neutral fluid codes, but at the cost of computational expense. Hybrid fluid-kinetic methods offer the promise of combining the advantages of the two."

Sefkow has more than ten years of experience in each computational paradigm and has served as a leader in designing and interpreting experiments at all three HED facilities. As Principal Investigator (PI), Sefkow "collaborates with professors and scientists to advance hybrid modeling efforts for HEDP and ICF science by leveraging (1) expertise in fluid and kinetic approaches; (2) computational techniques employed by existing codes like LILAC, DRACO, ASTER, HYDRA, LPSE, LSP, and VPIC; and (3) extensive collaborative connections with scientists developing those codes and conducting experiments at facilities around the country."

There are two objectives of the code development project. "The first is to develop and benchmark the particle-based fluid approach to modeling by including the best equation-of-state, conductivity, and opacity models normally used by magnetohydrodynamic codes such as LILAC, DRACO, ASTER, and HYDRA." The project team "will benchmark the model to long-pulse and short-pulse laser-physics simulations and experiments, as well as direct-drive, indirect-drive, and magnetic-drive implosions, which represent the three main approaches to fusion advocated by the national ICF community." Sefkow designed the first successful MagLIF (magnetic liner inertial fusion) experiments that established magnetically driven fusion as one of the DOE's three national approaches to ICF. The team will also benchmark particle-based ray-tracing laser–plasma interaction simulations to data, as well as other modeling efforts.

The second objective, to begin after completing the primary benchmarking objective, is to advance hybrid fluid-kinetic modeling techniques by investigating and improving their use in laser-driven and pulsed-power–driven systems.

Because Sefkow and his collaborators have worked closely with scientists from the nation's flagship laser and pulsed-power HED facilities, this project compared to other efforts encompasses experiments covering a broad range of parameter space. "The work enables an advanced research tool applicable to direct-drive targets, laser–plasma interaction in indirect-drive hohlraums (magnetized and unmagnetized) and high-density gases, fast ignition, shock ignition, coupled pulsed-power and laser systems, short-pulse laser interactions with plasmas and solids, dense plasma focus devices, plasma jets, laboratory astrophysics, and pulsed-power loads like solid liners, wire arrays, and gas puffs."

This project benefits from LLE research. Project funding will be used to educate and train new research assistants and students into the area of computational physics for HEDP and ICF. They will be identified, financially supported to participate, and encouraged to publish their findings as first authors. Sefkow and his collaborators have decades of experience writing in the necessary languages of these physics codes: Fortran, C/C++, Python, IDL, Basis, Yorick, and more. Their jobs as computational physicists are to write, test, debug, and maintain complex codes. Their publication track records are strong, so their expertise will enable the funded postdocs and students under this proposal to receive firsthand computational physics practices from leading experts.

Experiments and Simulations

Above, experiments (top row) and example hybrid electromagnetic CHIMERA simulations (bottom row) from the Omega Laser Facility (left),
National Ignition Facility (center), and the Z machine (right), are shown.