One of the main features of a new generation of spherical tokamaks (ST) is a significant increase in the toroidal field. In this paper we mainly address the impact on confinement and fusion performance, but also briefly discuss the other issues in a high field ST. Detailed transport simulations have been performed to predict the performance of the compact high field spherical tokamak ST40. We show that high confinement regimes with collisional (neoclassical) transport can be expected, even with just ohmic heating. In an auxiliary heating regime, as low as 1 MW of absorbed heating power may result in a hot ion mode in the 10 keV range of temperatures. Issues connected with specific features of the high field ST are discussed, i.e. limitations of applicability of confinement scalings for prediction of performance. These limitations are general but are strongly exposed in high field STs. However, we show that if the performance achieved on other STs can be extended to ST40 conditions, up to 0.5 MW of fusion power can be expected in DT operations.
Scaling of energy confinement time in the Globus-M spherical tokamak