Evolution of lower hybrid driven current during the formation of an internal transport barrier

Naito, Osamu; Cui, Z.*; Ide, Shunsuke; Suzuki, Takahiro; Oikawa, Toshihiro; Seki, Masami; Hatae, Takaki; Fujita, Takaaki; Kondoh, Takashi; Shirai, Hiroshi; Ikeda, Yoshitaka; Ushigusa, Kenkichi

Evolution of lower hybrid (LH) driven current profile was measured during the formation of internal transport barrier (ITB) in a reversed magnetic shear discharge. As the ITB developed, initially centrally peaked LH driven current profile gradually turned hollow and was sometimes accompanied by an off-axis peak in electron temperature profile followed by a sawtooth-like instability localized to the ITB. These observations indicate the concentration of LH power deposition at the ITB and suggest the difficulty of current profile control by LH waves once the ITB is established.