ARGONNE, Ill., May 16, 2017 — Every day, with little notice, the Earth is bombarded by energetic particles that shower its inhabitants in an invisible dusting of radiation, observed only by the random detector, or astronomer, or physicist duly noting their passing. These particles constitute, perhaps, the galactic residue of some far distant supernova, or the tangible echo of a pulsar. These are cosmic rays.
But how are these particles produced? And where do they find the energy to travel unchecked by immense distances and interstellar obstacles?
These are the questions Frederico Fiuza has pursued over the last three years, through ongoing projects at the Argonne Leadership Computing Facility (ALCF), a U.S. Department of Energy (DOE) Office of Science User Facility.
A physicist at the SLAC National Accelerator Laboratory in California, Fiuza and his team are conducting thorough investigations of plasma physics to discern the fundamental processes that accelerate particles. The answers could provide an understanding of how cosmic rays gain their energy and how similar acceleration mechanisms could be probed in the laboratory and used for practical applications.
While the “how” of particle acceleration remains a mystery, the “where” is slightly better understood. “The radiation emitted by electrons tells us that these particles are accelerated by plasma processes associated with energetic astrophysical objects,” says Fiuza.
The visible universe is filled with plasma, ionized matter formed when gas is super-heated, separating electrons from ions. More than 99 percent of the observable universe is made of plasmas, and the radiation emitted from them creates the beautiful, eerie colors that accentuate nebulae and other astronomical wonders.
The motivation for these projects came from asking whether it was possible to reproduce similar plasma conditions in the laboratory and study how particles are accelerated.
High-power lasers, such as those available at the University of Rochester’s Laboratory for Laser Energetics or at the National Ignition Facility in the Lawrence Livermore National Laboratory, can produce peak powers in excess of 1,000 trillion watts. At these high-powers, lasers can instantly ionize matter and create energetic plasma flows for the desired studies of particle acceleration.
To determine what processes can be probed and how to conduct experiments efficiently, Fiuza’s team recreates the conditions of these laser-driven plasmas using large-scale simulations. Computationally, he says, it becomes very challenging to simultaneously solve for the large scale of the experiment and the very small-scale physics at the level of individual particles, where these flows produce fields that in turn accelerate particles.
Because the range in scales is so dramatic, they turned to the petascale power of Mira, the ALCF’s Blue Gene/Q supercomputer, to run the first-ever 3D simulations of these laboratory scenarios. To drive the simulation, they used OSIRIS, a state-of-the-art, particle-in-cell code for modeling plasmas, developed by UCLA and the Instituto Superior Técnico, in Portugal, where Fiuza earned his PhD.
Read the full article at: https://www.alcf.anl.gov/articles/fields-and-flows-fire-cosmic-accelerators
Source: John Spizzirri, Argonne National Laboratory