Electron Cyclotron Heating Start-Up Experiments on TST-2

Abstract

Experiments were performed to study non-inductive current generation by electron cyclotron heating (ECH) in the TST-2 spherical tokamak. A magnetron (2.45 GHz/5 kW) and a horn antenna were used to inject either the O- or X-mode. The maximum plasma current does not depend on the injected wave polarization; however, it has a weak dependence on the vertical field configuration and is proportional to the vertical field. The initial current ramp-up rate depends on various operational parameters. The ramp-up rate increases with the injected EC wave power, and decreases with the filling pressure, resonance position (i.e., the toroidal field strength), and vertical field strength. It also depends on the magnetic field configuration. Conversely, the ramp-up rate does not depend on wave polarization, suggesting that multiple pass absorption of the EC wave is important.