Exploring the source of stars and planets in a plasma physics lab

Physicist Himawan Winarto with paper figures behind him. Credit: Collage by Elle Starkman / PPPL Communication Office

A new method for verifying a widely held but unproven theoretical explanation of star and planet formation has been proposed by researchers at the US Department of Energy (DOE) Princeton Plasma Physics Laboratory (PPPL) The method is enhanced by simulating the Princeton Magnetorotation Instability Experiment (MRI), a unique laboratory device designed to demonstrate the MRI process believed to have filled the cosmos with celestial bodies.

Cosmic dust

The new device, created to copy the process that causes clouds to spin from cosmic dust and plasma to collapse into stars and planets, it consists of two concentric cylinders filled with fluid that rotate at different speeds. The device seeks to replicate the instabilities thought to cause rotating clouds to gradually drop what is called their angular momentum and collapse into rising orbiting bodies. Such a moment keeps the Earth and other planets within their orbits.

“In our simulations we can see that MRI takes place in experiments,” said Himawan Winarto, a graduate student in the Princeton Program in Plasma Physics at PPPL and lead author of a paper in Physical Review E reporting the findings. “We are also proposing a new diagnostic system to measure MRI,” said Winarto, whose interest in the subject began as an intern at the University of Tokyo.Princeton University Partnership in Plasma Physics while he was a student at Princeton University.

The suggested system will measure the strength of the radial, or circular, magnetic field generated by the internal rotating cylinder in experiments. Since field strength is strongly related to expected turbulence instabilities, measurements can help determine the source of turbulence.

“Our overall objective is to show the world that we have no doubt seen the MRI effect in the laboratory,” said physicist Erik Gilson, one of Himawan’s mentors on the project and a co-author of the paper. “What Himawan is proposing is a new way of looking at our measurements to see the essence of MRI.”

Surprising results

The simulations have shown some surprising results. While MRI is normally only observed at a fairly high cylinder rotation speed, new findings show that instabilities can be seen very well before the upper limit of the experimental rotation speed is reached. “That means speeds much closer to the rates we’re using now,” Winarto said, “and projects the rotational speed we should aim to see on MRI.”

A major challenge in discovering the source of MRI is the existence of other effects that may act as MRI, but which are not actually the process. Among these deceptive effects are those called Rayleigh instability that split liquids into smaller packets and the Ekman circulation that changes the fluid flow profile. The new simulations clearly show “that MRI, rather than Ekman circulation or Rayleigh instability, dominates the flow of behavior in the region where the MRI is expected,” Winarto said.

The discoveries shed new light on the rising stars and planets that fill the universe. “The simulations are very useful to steer you in the right direction to help interpret some of the diagnostic results of the experiments,” Gilson said. “What we see from these results is that the MRI signals look like they should be able to be seen more easily in experiments than we previously thought.”

Reference: “Spatial representation of the parameters of the Princeton magneto-rotational instability experiment” by Himawan W. Winarto, Hantao Ji, Jeremy Goodman, Fatima Ebrahimi, Erik P. Gilson and Yin Wang, 24 August 2020, Physical Review E.
DOI: 10.1103 / PhysRevE.102.023113

Funding for this work comes from the U.S. Department of Energy Office of Science; NASA; and the Max-Planck-Princeton Center for Plasma Physics. Collaborators include PPPL physicists Fatima Ebrahimi and Yin Wang; Hantao Ji, a PPPL physicist and professor of astrophysics at Princeton University; and Jeremy Goodman, professor of astrophysics at Princeton University. Jean-Luc Guermond of the A&M University of Texas provided the widely used SFEMaNS simulation code on paper.

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