Simulations of control, perturbation, displacement and disruption in highly elongated tokamak plasmas

The control and evolution of highly elongated tokamak plasmas with large growth rates are simulated with the axisymmetric, resistive MHD code TSC in the geometry of the TCV tokamak. Simulations show that pressure perturbations such as sawteeth and externally programmed displacements create initial velocity perturbations in addition to equilibrium changes. It is demonstrated that these perturbations may be stabilized by low power, rapid response coils inside the passively stabilizing vacuum vessel, together with slower shaping coils outside the vessel. This method works because coils inside the vessel do not have a flux penetration delay. Vertical disruption induced voltages and forces on the rapid coils and the vessel are investigated to establish coil and vessel design requirements. A model is proposed and used to estimate the additional vertical force due to poloidal currents, which is comparable to the force from toroidal currents.