Current and pressure gradient triggering and nonlinear saturation of low-n edge harmonic oscillations in tokamaks

It is shown that non-axisymmetric free-boundary equilibrium computations represent nonlinearly saturated external kink modes and external kink-like sidebands coupled to pressure-driven infernal modes. In this study, two different driving mechanisms for external kink type-modes are identified. It is found that standard current-driven external kinks are linearly unstable, and nonlinearly stable in a wide parameter range, especially where qedge