Theory and Simulations
Research Focus
The Theory and Simulation group of the High-Energy-Density Science Division @ SLAC uses plasma theory and massively parallel kinetic simulations to explore the plasma processes that characterize extreme states of matter, ranging from dense collisional plasmas to relativistic collisionless regimes.
Our research covers three main areas of High-Energy-Density physics associated with discovery plasma science and applications relevant to fusion energy science.
Magnetic field dynamics and particle acceleration in plasmas
Astrophysical plasmas are known to be efficient particle accelerators, from solar flares to gamma-rays bursts. In spite of a wealth of observations and proposed models, clarifying the various acceleration mechanisms in these extreme environments remains a long-standing scientific challenge. This arises from the complexity of the kinetic and highly nonlinear interplay between the dynamics of plasma flows, magnetic fields, and high-energy particles, which operate at different scales. In our work we use first principles particle-in-cell simulations to explore particle acceleration in plasmas associated with collisionless shocks, magnetic reconnection, and turbulence. We also work closely with experimental teams in the design and interpretation of high-energy-density laser-plasma experiments, where these processes can be directly probed and connected, through appropriate scaling laws, with astrophysical and laboratory plasma models.
Compact secondary sources from laser-plasma interactions
Plasmas can sustain electric fields that are several orders of magnitude larger than conventional accelerator technology. In our work, we aim to understand how to control and optimize intense laser-plasma interactions to accelerate high-quality beams of electrons and ions for a variety of scientific and technological applications: from diagnostics for fusion plasmas to medical imaging and therapy.
Basic properties of fusion plasmas
At the high energy densities and temperatures associated with laboratory fusion plasmas, the fundamental assumptions of hydrodynamic theory can break down, and it is expected that kinetic effects begin to play an important role. We are interested in exploring this transition between hydrodynamic and kinetic plasma regimes associated with the dynamics of interpenetration and stability of multi-species high-energy-density plasmas relevant to fusion.
Research Tools
A strong component of our research is based on the use of massively parallel Particle-in-Cell (PIC) simulations of plasmas. This method describes plasmas as particles interacting self-consistently via the electromagnetic fields they themselves produce, which are calculated using Maxwell’s equations. To the extent that quantum effects can be neglected, the PIC method provides a first principles description of plasma dynamics and is thus ideally suited for studying the microphysics of plasmas. The main code that we use is OSIRIS, which is capable of efficiently modeling large-scale plasma problems on the largest supercomputers. OSIRIS has been used in multiple areas of plasma physics research, including intense laser-plasma interactions, inertial confinement fusion, and extreme astrophysical scenarios. It has also been successfully used in the design and interpretation of intense laser- and beam-plasma experiments worldwide.
Connecting Simulations with Laboratory Experiments
An important aspect of our work involves connecting our models and simulations with laboratory experiments that can test our predictions and lead to further improvements in our understanding of plasmas under extreme conditions. In our group we collaborate with several experimental teams from universities and laboratories worldwide that use word-class laser facilities such as LCLS at SLAC, NIF at LLNL, and OMEGA at LLE to explore the physics of high-energy-density plasmas. As part of these collaborations, we have developed a suite of codes and numerical models to produce synthetic experimental diagnostics from simulation data, including x-ray phase-contrast imaging, proton radiography, and Thomson scattering. In addition to enabling detailed comparisons between simulations and experiments, these tools also play an important role in the design of experiments and in the improvement and optimization of experimental diagnostics.
