The solar corona, an ethereal halo of plasma that\u2019s a million degrees hotter than the Sun\u2019s surface<\/a>, is home to magnetic flux ropes: twisted tubes of plasma that behave like electrified garden hoses. These ropes, charged and frozen into magnetic fields, are the engines behind solar flares and coronal mass ejections. But until now, scientists didn\u2019t fully understand what happens when these ropes braid together.<\/p>\n Using a vacuum chamber and a pair of electrodes, Bellan and Zhang recreated miniature solar flares in the lab, just 10 to 50 centimeters long. What emerged was a stable double helix: two flux ropes spiraling around each other in perfect magnetic balance.<\/p>\n \u201cWe have two electrodes inside the vacuum chamber<\/a>, which have 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,\u201d Zhang explains.<\/p>\n And unlike previous assumptions, the ropes didn\u2019t merge or collapse; they held their shape without tending to twist tighter or untwist.<\/p>\n In their new study, Zhang and Bellan show that the double-helix structure formed by braided magnetic flux ropes can reach a stable balance, and that this balance can be predicted using math.<\/p>\n While scientists already understand single flux ropes well, braided ones, especially when both strands carry electric current in the same direction\u2014have been more mysterious. Most models focused on the opposite case, where currents flow in opposite directions, but that setup is rare in nature.<\/p>\n The same-direction current setup is crucial because it\u2019s prone to twisting and expanding due to magnetic forces, a behavior seen in both solar flares and lab experiments. These effects don\u2019t happen when the currents cancel each other out, as in the opposite-direction case.<\/p>\n Scientists used to think that when two braided magnetic flux ropes carry current in the same direction, they\u2019d naturally merge, because parallel currents attract each other magnetically. But in 2010, researchers at Los Alamos National Laboratory discovered something surprising: instead of merging, these flux ropes actually bounce off each other when they get close.<\/p>\n \u201cThere was clearly something more complicated going on when the flux ropes are braided, and now we have shown what that is. Suppose you have electrical currents flowing along two helical wires that wrap around each other to form a braided structure, as seen in our lab. In that case, the components of the two currents flowing along the length of the two wires are parallel and attract, but the components of the two currents flowing in the wrapping direction are anti-parallel and repel.\u201d<\/p>\n \u201cThis combination of both attractive and repulsive forces means there will be a critical helical angle at which these opposing forces balance, producing an equilibrium. If the helical flux ropes twist tighter, there will be too much magnetic repulsion; if they twist more loosely, there will be too much magnetic attraction. At the critical angle of twist, the helical structure arrives at its lowest energy state, or equilibrium.\u201d<\/p>\n To crack the mystery of how braided flux ropes behave, Zhang took on the challenge of building a mathematical model, something no one had done before. Using what Bellan calls \u201cbrute force mathematics,\u201d Zhang developed equations that work across different flux tube setups, including the tricky double-helix braids. His model revealed that these ropes can reach a stable state where magnetic attraction and repulsion perfectly balance out.<\/p>\n And there was a bonus: Zhang\u2019s equations didn\u2019t just predict equilibrium, they also mapped out the magnetic fields inside and outside the ropes, along with the current and pressure within. As Bellan put it, this gave scientists a complete picture of how these twisted plasma structures behave.<\/p>\n![\"Four](\"https:\/\/www.newsbeep.com\/uk\/wp-content\/uploads\/2025\/08\/Four-braided-structures.webp.webp\"\/)
Four braided structures. (a) astrophysical jet M-87, 3000 light years long; (b) Double Helix Nebula, 70 light years long; (c) solar prominence, 3000 kilometers long; (d) solar loop manufactured in Bellan lab at Caltech, 3 centimeters long.
\nCredit: (a) Passeto et al., Sophia Dagnello, NRAO\/AUI\/NSF; (b) NASA\/JPL-Caltech\/M. Morris (UCLA); (c) High Altitude Observatory Archives; (d) Yang Zhang, Caltech Bellan Plasma Lab<\/p>\n