By California Institute of Technology
September 4, 2025

Caltech experiments uncovered a stable double helix state in plasma flux ropes. The same principles explain cosmic structures such as the Double Helix Nebula.

Research into the Sun’s outer atmosphere has led Caltech applied physics professor Paul Bellan and his former graduate student Yang Zhang (PhD ’24) to identify a previously unknown equilibrium state of magnetic fields and the plasma they contain. The solar corona, the Sun’s outermost atmospheric layer, is far less dense than the surface, yet it reaches temperatures a million times higher.

This region is dominated by powerful magnetic fields that trap plasma, a hot mixture of charged particles (electrons and ions). The newly identified equilibrium, known as a double helix, is not limited to the corona but also appears in much larger cosmic systems, including the Double Helix Nebula near the center of the Milky Way.

Solar activity such as flares often takes the shape of magnetic flux ropes, which are twisted tubes of magnetic field filled with plasma. One way to picture a flux rope is to imagine a garden hose filled with plasma and wrapped in a spiral stripe. Along the hose runs an electric current, while the spiral represents the helical magnetic field surrounding it. Because plasma carries electric charge, it conducts current and becomes bound—or “frozen”—to the magnetic field.

These magnetic flux ropes appear across a remarkable range of scales, from small laboratory setups to massive solar flares spanning hundreds of thousands of kilometers. In astrophysics, similar rope-like structures can extend across hundreds or even thousands of light-years.
Creating plasma braids in the lab

Inside a large vacuum chamber, Bellan and Zhang (now a NASA Jack Eddy postdoctoral fellow at Princeton) created miniature versions of solar flares measuring just 10 to 50 centimeters in length. Yang describes the process: “We have two electrodes inside the vacuum chamber, which has coils producing a magnetic field spanning the electrodes. Then we apply high voltage across the electrodes to ionize initially neutral gas to form a plasma. The resulting magnetized plasma configuration automatically forms a braided structure.”

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