Plasma current ramp-up by waves in the lower hybrid frequency range on TST-2

Noninductive plasma current ($I_{\rm p}$) ramp-up by RF power is being studied on TST-2. A tokamak configuration with $I_{\rm p}\simeq 1\rm\,kA$ is formed spontaneously by injecting RF power (2.45\,GHz, 200\,MHz or 21\,MHz). Subsequent $I_{\rm p}$ ramp-up is achieved by gradual increases of RF power and vertical field. As $I_{\rm p}$ is ramped up, the fraction of RF driven current becomes larger, and a clear dependence on wave directionality becomes observable. Up to 12\,kA of $I_{\rm p}$ has been achieved by launching a traveling wave in the co current drive direction. X-ray measurements indicate gradual increases of electron temperature and superthermal electron population. An attempt is being made to obtain information on superthermal electrons from directional Langmuir probe measurements.