Characteristics of High Poloidal Beta (βp) Plasma Formed by Electron Cyclotron Waves in Spherical Tokamak QUEST

In spherical tokamak QUEST, plasma with high poloidal beta (βp) is obtained by injecting Electron Cyclotron Waves (ECW) into the Ohmic target plasma. With high βp, the plasma shape is transformed from an inboard limiter configuration to a natural divertor with the appearance of an poloidal null at the inboard side. By applying high vertical magnetic field (Bz), this high βp plasma is sustained. With suitable control of the equilibrium, effective current drive is observed in the later part of the discharge along with strong recharging of the Ohmic circuit and the Ip is sustained for > 1 s.