First Measurement of Electron Temperature and Density Profiles for Spherical Tokamak Plasmas Sustained by Lower Hybrid Waves

In this research, the profiles of electron temperature Te and density ne 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 Te profile was hollow and the ne profile was like bell-shaped. Te and ne 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.