Ion heating characteristics of merging spherical tokamak plasmas for burning high-beta plasma formation

High-power ion heating of merging spherical tokamak (ST) plasma has been investigated using TS-3U, TS-4, and UTST at the University of Tokyo for future direct access to burning high-beta ST plasma without using any additional heating. We developed a two-fluid/kinetic interpretation of the promising scaling of ion heating energy that increases with the square of reconnecting magnetic field B _rec ∼ poloidal magnetic field B _p . We find that reconnection heating creates interesting high-beta ST plasmas with hollow currents and broad/hollow T _i profiles. These high-beta ST plasmas often have reversed-shear or absolute minimum-B profiles, depending on their reconnection heating power and q-values.