Even a celestial body as familiar as the sun has a few secrets. Above the sun’s visible surface, hot gases made up of charged particles stretch into space to form the sun’s superheated outer layers, including the streaky corona, which can be seen looking like a lion’s mane during a total solar eclipse. Some process heats up these plasmas in the corona to millions of degrees and makes them speed away from the sun as solar wind.
Exactly how these plasmas escape the sun’s magnetic fields is still a mystery. “A lot of the open questions about the sun eventually come down to the magnetic field” because magnetic fields govern much of the sun’s activity, said Therese Kucera, an astrophysicist at NASA’s Goddard Space Flight Center who studies the sun’s atmosphere.
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So a team of researchers decided to try to re-create the sun’s magnetic field structure in a ball of plasma in their laboratory.
How do you make a sun in the lab?
The simplest model for the sun’s magnetic field would be a bar magnet, or dipole, which has a north and south pole. Its magnetic field extends from one pole to the other.
Of course, the sun is more complicated than a bar magnet. The sun spins, twisting the magnetic field into a swirling pattern known as the Parker spiral. And the streams of plasma emanating from the sun pull parts of the magnetic field with them like rubber bands, stretching the loops all the way to the edges of the solar system.
A research team at the University of Wisconsin, Madison, built each of these factors into their laboratory model. Inside a 3-meter-wide plasma containment chamber — the “Big Red Ball” — the team placed a cylindrical permanent magnet about 10 centimeters wide and 10 centimeters long. This was their starter sun. They then filled the ball with a plasma made from helium gas and drove an electrical current through it, which created a force on the plasma that made it spin around the dipole.
“That creates a spinning plasma in a dipole magnetic field, similar to the sun,” said Ethan Peterson, a plasma physicist at Wisconsin. With this technique, the team was able to successfully re-create the shape of the Parker spiral, as they describe in a paper published today in Nature Physics.
