Status and future prospects of the spherical torus research. Theory and simulation of spherical torus plasmas

Characteristic properties of micro-scale as well as macro-scale stabilities in a spherical torus, which originate from the nature of the low aspect ratio in the geometrical configuration, are described. In particular, recent theoretical and simulation research on the neo-classical tearing mode, the trapped electron ηi mode, the kinetic ballooning mode, the TAE (Toroidicity-induced Alfven Eigenmode) mode, optimization of configurations, and relaxation phenomena in spherical tokamaks are discussed. (author)