Dependence of wall stabilization and q_a on sawtooth triggering of saturated 2/1 tearing modes from a coupled kink-tearing mode in HBT-EP

Accurate modeling of tearing modes will be crucial to ensuring the reliability of future fusion reactor designs. This poster presents experimental data on the interactions of 2/1 tearing modes with edge kink modes, sawteeth, and a conducting wall, on the HBT-EP tokamak. Using a 4-fan 64 cord poloidal Extreme Ultraviolet (pEUV) diagnostic and tomographic inversion, the internal structures of modes in the plasma are reliably uncovered. Many diverse diagnostic signals are combined in a multidiagnostic Singular Value Decomposition (mdSVD), showing the dominance in typical perturbed signals of a 2/1 tearing mode rotating in phase with an edge 3/1 kink mode. This coupled 2/1-3/1 tearing kink system is observed to rapidly transition from low amplitude into a large saturated 2/1 tearing mode, at a specific sawtooth crash. Leveraging HBT-EP's unique radially adjustable outboard resistive walls, it is observed that as the wall stabilization is increased, the q=2 rational surface must be progressively closer to the surface of the plasma for the tearing mode to be triggered and remain saturated. It is observed that this dependency is not captured by Δ' in the absence of additional driving terms, nor explained by changes to the equilibrium profile.