![]() How the code breaks up the problem and maps the pieces to computer processors is an important consideration, as it helps determine the maximum problem size and the speed at which the problem can be solved. The Cimarron team incorporated functions derived from fundamental laws of quantum mechanics into ddcMD, which enabled the code to accurately calculate electron interactions at both length scales during the course of a simulation. To do so, the code needed to account for electrons’ short-range interactions-collisions with protons and other electrons-and their longer range interactions, particularly their attraction to and repulsion of other particles from electric charge, known as the Coulomb force. “With the Cimarron code, we broke the electrons out and let them do what they wanted,” notes Murillo, evoking the project’s name, which means “wild and untamed” in Latin-American Spanish. The problem was that MD is typically used to simulate the movement of atoms, molecules, or ions, but almost never electrons. Given the significant role electrons play in plasma behavior, the code had to describe them accurately. The detached electrons enable the plasma to act as a whole rather than simply a cluster of individual particles. A plasma is a cloud of charged particles (ions and electrons) created when electrons detach from their respective atoms and molecules. ![]() Modifying ddcMD, initially created for materials science applications, for plasma studies posed a computational challenge. MD simulations allow researchers to study the behavior of matter on nanometer (billionth-of-a-meter) and femtosecond (one-quadrillionth-of-a-second) scales, while hydrodynamics simulations are used to study matter on, at minimum, micrometer and picosecond scales-a million times larger. MD simulations follow the trajectory of each particle in a system, while hydrodynamics simulations treat particles as a fluid that flows through a mesh. MD codes offer a different approach to modeling compared to traditional hydrodynamics codes. The Livermore-developed massively parallel molecular dynamics (MD) code ddcMD served as the backbone for the initiative. Over the course of eight years, Cimarron grew to encompass collaborators from three national laboratories and five universities, including theorists for modeling, experimentalists to gather validation data, computational physicists to run simulations, and computer scientists to keep calculations running smoothly on some of the largest and most sophisticated computers available. The initiative was designed to predict and measure the properties of dense plasmas. The research team explored the virtual plasma concept through the Cimarron project, an ambitious initiative funded by the Laboratory Directed Research and Development Program. “The regimes we care about are extreme and complex, and experimental data is limited with which we can compare our simulations, so we have to rely on theory and approximations.” Graziani and colleagues including Los Alamos National Laboratory’s Michael Murillo, an expert in matter at extreme conditions, and Livermore computational physicist Fred Streitz, formulated a different approach to plasma studies by creating a “virtual plasma” and probing it just as experimentalists would diagnose a real one. “While investigating burn physics for programmatic applications, I began to question the fidelity of the plasma models we were using in our radiation–hydrodynamics codes,” says Graziani. Livermore physicist Frank Graziani is working to facilitate the study of plasma physics through more realistic computational models. Studying these conditions on Earth, in the absence of nuclear testing, is no easy task. ![]() Such plasmas occur in stellar interiors, giant planets, nuclear weapons detonations, and inertial confinement fusion (ICF) experiments. Of particular interest to Livermore researchers are nonequilibrium (multi-temperature) plasma systems that exist at extreme conditions: temperatures of a million or more kelvins, pressures of a million or more times Earth’s atmosphere at sea level, and densities equivalent to those of many metals. Plasmas are involved in a wide range of atmospheric and astrophysical phenomena, from lightning flashes to accretion disks around black holes. Taming the Wild Frontiers of Plasma Science
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |