Assessment of vertical stability for negative triangularity pilot plants

Negative triangularity (NT) tokamak configurations in conformal wall geometries are susceptible to vertical instability. NT equilibria are stabilized in positive triangularity (PT) vacuum vessels due to increased proximity to the wall on the outboard side, but this scenario is undesirable due to reduced vertical gaps which give less margin for control recovery. Instead, informed positioning of stabilizing plates improves vertical stability in NT configurations on par with metrics expected in PT scenarios. For high elongation NT geometries, the optimal setup with plates on the outboard side of the device reduces instability growth rates to 16% of their baseline value. For lower elongations, integration of passive stabilizers with divertor concepts significantly improves vertical stability. Plates on the inboard side of the device are also enabled for NT, providing opportunity for spatial separation of vertical stability coils and passive stabilizers. These studies illustrate how to optimize passive vertical stability in NT fusion pilot plants [1].

[1] S. Guizzo et al 2024 Plasma Phys. Control. Fusion 66 065018