Vertical Displacement Events in Shaped Tokamaks

Computational studies of vertical displacement events (VDE's) in shaped tokamaks are presented. The calculations are performed with our nonlinear, 3D resistive MHD code, CTD, which can efficiently treat resistive walls and free boundary displacements in moderately-shaped geometries. This work has a number of related goals: First, the mechanisms for generation of halo currents, the paths taken by them in the plasma and surrounding conductors, and their relative magnitude are elucidated. Second, the coupling between an n=0 vertical instability and an n=1 external kink mode is examined to offer a possible explanation for the nonuniformities observed in the poloidal halo currents during VDE's, and the forces generated by them on the plasma-facing components. Finally, effects of a rotating liquid metal wall on the equilibrium and n=0 stability of elongated plasmas are briefly discussed.