Using supercomputing resources at the Argonne Leadership Computing Facility (ALCF), an international team of researchers carried out simulations to design groundbreaking laser experiments that shed light on the mysterious origins of cosmic magnetic fields.
Co-led by researchers from the University of Rochester and the University of Oxford, the team is investigating a phenomenon known as turbulent dynamo, a mechanism thought to play an important role in generating the magnetic fields present in planets, stars, galaxies, and galaxy clusters. Studying this process could also lead to a better understanding of the evolution of the universe.
The team’s simulations at the ALCF helped determine the parameters needed to recreate and study turbulent dynamo in a laboratory for the first time via experiments conducted at the University of Rochester’s Omega Laser Facility at the Laboratory for Laser Energetics. The mechanism had previously been studied only through theoretical calculations and numerical simulations.
“These laser-driven plasma experiments enabled us to reproduce the turbulent dynamo mechanism and, for the first time in the laboratory, access the viscosity-dominated regime that is relevant to most plasmas in the universe,” said Petros Tzeferacos, an astrophysicist at the University of Rochester. “This was also the first instance in which we’ve been able to successfully record time-resolved measurements of the properties of the mechanism, including the growth rate of the magnetic field, which could previously only be studied via simulation.”
Utilizing an array of lasers—whose cumulative power was equivalent that of some 10,000 nuclear reactors—to experiment with conditions comparable to those found in the plasma-heavy areas of space found between galaxy clusters where it is believed to be a factor, the researchers demonstrated that the turbulent dynamo mechanism can rapidly generate large-scale magnetic fields. Their findings were detailed in a paper published in the Proceedings of the National Academy of Sciences earlier this year.
In an earlier study, the team used ALCF simulations to design Omega Laser Facility experiments that proved the existence of the turbulent dynamo mechanism. For the new experiments, the researchers again leveraged ALCF supercomputers to construct a novel experimental platform using numerical simulations performed with FLASH, a publicly available simulation code capable of accurately modeling laser-driven laboratory plasma experiments.
The platform consists of a pair of plastic foils that are driven with 20 OMEGA laser beams; each beam is capable of focusing up to 500 joules of energy onto a target less than 1 millimeter in diameter in some billionths of a second. The laser ablation launches a pair of magnetized plasma flows that propagate through offset grids, collide, shear, and create a hot, turbulent plasma. The turbulent plasma achieves a regime where turbulent dynamo can amplify the advected seed magnetic fields to magnetic energies comparable to the kinetic energy of the stochastic motions.
These experiments now provide strict constraints to existing models and help explain astronomical measurements. The efficient amplification of magnetic fields at large scales seen in the experiments could explain the origin of large-scale fields observed in galaxy clusters, which are not captured by current idealized simulations.
“Our team’s efforts answer key astrophysics questions and establish laboratory experiments as a component in the study of turbulent dynamo,” Tzeferacos explained.
The ALCF is a U.S Department of Energy (DOE) Office of Science user facility located at DOE's Argonne National Laboratory. The team used ALCF computing resources through an award from DOE’s ASCR Leadership Computing Challenge.
The Argonne Leadership Computing Facility provides supercomputing capabilities to the scientific and engineering community to advance fundamental discovery and understanding in a broad range of disciplines. Supported by the U.S. Department of Energy’s (DOE’s) Office of Science, Advanced Scientific Computing Research (ASCR) program, the ALCF is one of two DOE Leadership Computing Facilities in the nation dedicated to open science.
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