Comparison of MHD stability between positive- and negative- triangularity tokamak plasmas with internal transport barriers

Ideal magnetohydrodynamics (MHD) stability of tokamak plasmas is compared between positive and negative triangularity cross sections. The bootstrap current is included that is determined from the density and temperature profiles. This is crucial for a DEMO reactor design. The density and temperature profiles are chosen to have internal transport barriers (ITBs), which are necessary if an H-mode edge cannot be expected. The ideal MHD stability is examined in a wide range of the ITB position and the central temperature. We confirmed that ballooning modes are prone to be unstable when the ITB is located near the plasma edge for negative triangularity. Internal kink modes become dominant instability when the ITB is located inner side of the plasma for both positive and negative triangularities. We have succeeded to stabilize both ballooning and internal kink modes by introducing additional currents to control the safety factor profiles in a favorable manner.