First measurement of electron temperature and density profiles for spherical tokamak plasmas sustained by lower hybridwaves

In this research, the profiles of electron temperature T_e and density n_e for a spherical tokamak with the plasma current sustained by lower hybrid waves alone have been measured for the first time using Thomson scattering diagnostics in the TST-2 spherical tokamak device. The T_e profile was hollow and the n_e profile was like bell-shaped. T_e and n_e near the plasma center were 6 eV and 6 × 1017 m^-3, respectively, leading to a pressure of 0.6 Pa. On the other hand, whole pressure at the plasma center calculated using an equilibrium reconstruction code EFIT was around 20 Pa. Therefore, it is suggested that fast electrons play an important role in the plasma equilibrium.