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The radial wind created in the plasma stretches the magnet field out radially forming a current sheet and spiraling magnetic field. 3-axis Hall probe measurements are shown as an axisymmetric 3D field-line rendering.
The radial wind created in the plasma stretches the magnet field out radially forming a current sheet and spiraling magnetic field. 3-axis Hall probe measurements are shown as an axisymmetric 3D field-line rendering.
[Figures are from E. E. Peterson et al. Nat. Phys. July 2019]

The Science

The Sun is a spinning ball of plasma that generates its own magnetic field. Fueled by the nuclear fusion in its core, the Sun spews plasma out into the solar system. This process forms the solar wind. The solar wind flows outward at great speed, pulling the magnetic field along with it as it gets twisted into a spiral (called a Parker spiral) by the Sun’s rotation. This interaction between the solar wind and magnetic field is crucial for understanding how the solar wind is accelerated. This experiment recreated this interaction at a very small scale in the laboratory for the first time.

The Impact

This experiment successfully recreated the Parker spiral. In doing so, scientists observed magnetic reconnection (the process by which magnetic energy turns into particle energy) and plasma blob formation in the lab. These processes are strikingly similar to phenomena that fuel the solar wind.  By understanding the causes behind acceleration and heating in the solar wind, we may be better able to predict space weather events. These events can harm communications and power infrastructure. They can also pose a threat to astronauts’ safety.

Summary

The solar wind sweeps away the Sun’s magnetic field. As the Sun rotates, the magnetic field bends into a spiral structure known as the Parker spiral. The region where the magnetic field begins to stretch and twist is believed to be highly dynamic, but has been largely unexplored. 

This publication described a laboratory model of this spiral structure. This model can be used as an experimental method of studying the solar wind, complementing space missions such as NASA’s Parker Solar Probe mission.

The team recreated the Parker spiral in the laboratory by forcing a helium plasma to rotate in the Big Red Ball device (a plasma confinement vessel). Once the plasma spun fast enough, its magnetic field formed a spiral. The authors then used measurements of the magnetic structures and plasma flows taken from the probes in the Big Red Ball to calculate the dynamics of the solar wind.

The authors conclude that, although the Parker spiral is far more complex and expansive than its laboratory equivalent, this plasma model accurately reproduces the structure of the Sun’s magnetic field. They suggest that it can be used to further examine the origin and evolution of the solar wind.

Contact

Mr Ethan E. Peterson (University of Wisconsin–Madison),
ethan.peterson@wisc.edu, 608 260-0879

Prof Jan Egedal (University of Wisconsin–Madison),
egedal@wisc.edu, 608 262-3628

Prof Cary B. Forest (University of Wisconsin–Madison),
cbforest@wisc.edu , 608 263-0486

Funding

The present work was supported by the NASA Earth and Space Sciences–Heliophysics Division Fellowship. The Big Red Ball facility was originally constructed with support from the National Science Foundation and is now operated by the Department of Energy’s Office of Science as a collaborative user facility.

Publications

E.E. Peterson, D.A. Endrizzi, M. Beidler, K.J. Bunkers, M. Clark, J. Egedal, K. Flanagan, K.J. McCollam, J. Milhone, J. Olson, C.R. Sovinec, R. Waleffe, J. Wallace, and C.B. Forest, “A laboratory model for the Parker spiral and magnetized stellar winds.”  Nature Physics. 15, pg. 1095–1100 (2019). [DOI: 10.1038/s41567-019-0592-7]

Related Links

Researchers recreate the sun’s solar wind and plasma “burps” on Earth, University of Wisconsin