Mathematical Model of the Stabilization of Magnetic Islands with Radio Waves in Tokamaks

What is it about?

In a tokamak, magnetic fields are used to confine and control the plasma along a desired trajectory. However, the plasma can sometimes develop what are called tearing instabilities, where the magnetic field gets ripped apart and forms magnetic islands. These islands are patches of unstable, closed magnetic surfaces. They can cause violent disruptions in the plasma which can be dangerous and limit the effectiveness of tokamaks. It has been shown that radio frequency (RF) waves can be used to drive electric currents in the center of magnetic islands, and that the currents can counteract the tearing instability. In RF current condensation, there is a nonlinear feedback loop where the wave heats up the center of the island, which in turn, allows more power to be deposited, and further heats up the island. The current drive is enhanced by the increase in the deposited power. In our work, we develop a simple model for RF current condensation that outlines how power from an incoming RF wave is distributed within an island. Our work helps better understand how local power depositions profiles vary depending on key experimentally relevant parameters.

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Photo by John Doyle on Unsplash

Photo by John Doyle on Unsplash

Why is it important?

A more developed picture of RF current condensation can help stabilize magnetic islands in tokamaks and, in turn, allow for more efficient fusion. Our work provides further guidance to plan experiments for island stabilization. Finally, we hope our work will allow for improved semi-analytical models.

Perspectives