Non-linear instability at large vertical displacements in the MAST tokamak

Data from forced Vertical Displacement Event (VDE) experiments in the Mega Ampère Spherical Tokamak (MAST) indicate that the plasma is highly destabilized above z displacements of ∼0.4 m. Previous work investigating the plasma response to vertical plasma perturbations in MAST had found it to be more non-linear than an equivalent conventionally shaped tokamak. Further investigation into the stability of the plasma at high z displacements is done using a linear vertical stability code. Theoretically it is found that the plasma becomes ideally unstable from z ∼ 0.8 m, corresponding to a significant acceleration of the vertical position experimentally.