Credit: Image courtesy of Bardoczi, L., Logan, N.C., and Strait, E.J., Neoclassical Tearing Mode Seeding by Nonlinear Three-Wave Interactions in Tokamaks. Physical Review Letters 127, 055002 (2021).
Magnetic island structures can exist in a tokamak at different radial locations (left), but couple to each other as their speeds match. The coupling strength is indicated in the combined value of the different wave frequencies (right).