STUDY OF 70GHZ SECOND HARMONIC X-MODE ECCD IN HELIOTRON J

Second harmonic X-mode electron cyclotron current drive (ECCD) experiments have been made in Heliotron J by using an upgraded EC launching system. A focused Gaussian beam is injected with the parallel refractive index, N-ll, ranging from -0.05 to 0.6. According to ray tracing calculations, the focused Gaussian beam makes the EC power absorption localized, Delta rho<0.2, modifying the rotational transform profile. The experimental results show that the EC driven current can be controlled by N-ll, and it depends on the local magnetic field structure where the EC power is deposited. A large increase in ECE signals has been observed when the EC current was driven, indicating important role of high-energy electrons on the ECCD.