A 3D disruption of magnetic fields
Scientists traced the collapse to the 3D mess of strong magnetic fields. “We proposed a new way of understanding the [disordered] field lines, which were generally ignored or poorly modeled in previous studies,” said Min-Gu Yoo, postdoctoral researcher at PPPL and lead author of the new study.
Magnetic fields are used in fusion facilities as substitutes for the powerful gravity that holds fusion reactions in place in celestial bodies. However, in laboratory experiments, these fields are disordered by plasma instability resulting in super hot plasma rapidly escaping confinement. The resulting heat can damage the walls of the melting plant.
“In the event of a major disturbance, the land lines become completely [disordered] like spaghetti and quickly connect to the wall with very different lengths,” said lead research physicist Weixing Wang, PPPL adviser to Yoo and co-author of the paper. “It brings huge plasma thermal energy against the wall.”
Scientists around the world are working to capture and direct the process of atomic fusion on Earth to develop a clean, carbon-free, and possibly inexhaustible source of energy that can generate electricity.
A setback that previously remained unknown was the 3D shape, or topology, of the disordered field lines caused by turbulent instability. This topology was responsible for creating tiny hills and valleys where some particles were trapped while others rolled down the hills and affected the walls of the facility.
“The existence of these hills is responsible for the rapid temperature collapse, the so-called thermal quenching, as they allow more particles to escape to the wall of the tokamak,” Yoo said. “What we have shown in the paper is how to draw a good map to understand field line topology. Without magnetic hills, most of the electrons would have been trapped and could not produce the thermal quenching observed in experiences.