Equilibrium features of bean-shaped spherical tokamak plasmas with an ergodic limiter

Equilibrium simulations of spherical tokamak bean-shaped plasmas in natural divertor geometry with an Ohmic regime are presented for the first time. Preliminary results in a non-self-consistent scenario suggest higher (factor up to 2) beta values can be attained for these plasmas compared to the more usual spherical tokamak natural divertor D-shaped geometry. This can be attained simultaneously (but independently) with setting an edge localised ergodization as observed via a Poincaré mapping, using a low level of perturbation to the plasma current (~2 percent). In combination with the closer proximity of the bean-shaped plasmas to the in-vessel limiters (also observed here) this leads to a higher beta limit which extrapolates favorably for a more compact reactor based in the spherical tokamak concept which is thus more economical and has a more even thermal power load.