The whims of the solar winds – charged particles flowing from the Sun’s atmosphere – can interfere with systems that are now crucial for modern life, such as satellites and GPS services – but these winds can be difficult to anticipate. Researchers from Princeton University and the Princeton Plasma Physics Laboratory (PPPL) used supercomputing power to reproduce these solar winds, helping illuminate how our planet interacts with these cosmic forces.
To understand solar winds, the researchers ran supercomputer-enabled simulations of a jet of plasma in motion – a recreation of a common laboratory experiment technique called a “plasma piston.” “Think of a boulder in the middle of a fast-moving stream,” said Derek Schaeffer, the associate research scholar from Princeton University who led the research team, in an interview with PPPL. “The water will come right up to the front of the boulder, but not quite reach it. The transition area between quick motion and zero [standing] motion is the shock.”
These plasma jets, which can be produced by cosmic events like supernovae, produce collisionless shock waves as they pass through slower plasma in space. These same shock waves are produced by Earth as it moves through solar winds, influencing how the winds interact with our magnetosphere. The researchers simulated the shock waves on the Titan supercomputer at the Oak Ridge Leadership Computing Facility. Titan, which boasted 18,688 AMD Opteron CPUs and 18,688 Nvidia K20 GPUs and delivered nearly 18 Linpack petaflops, was decommissioned last August.
The simulations helped the researchers understand signs of shock formation and isolate phenomena that were mistakable for shocks. “By being able to distinguish a shock from other phenomena, scientists can feel confident that what they are seeing in an experiment is what they want to study in space,” Schaeffer said.
“During laser plasma experiments, you might observe lots of heating and compression and think they are signs of a shock,” Schaeffer continued. “But we don’t know enough about the beginning stages of a shock to know from theory alone. For these kinds of laser experiments, we have to figure out how to tell the difference between a shock and just the expansion of the laser-driven plasma.”
The PPPL simulations are a major step toward making those distinctions. The researchers are now working on improving the resolution and realism of the simulations, and they hope to take their ideas into the real world in the near future to see whether their simulations are representative of reality.
“We’d like to put the ideas we talk about in the paper to the test,” Schaeffer said.
The research discussed in this article was published as “Kinetic simulations of piston-driven collisionless shock formation in magnetized laboratory plasmas” in the April 2020 issue of Physics of Plasmas. It was written by D. B. Schaeffer, W. Fox, J. Matteucci, K. V. Lezhnin, A. Bhattacharjee and K. Germaschewski and can be accessed here.