Progress of ECRH by EBW in over-dense plasmas and controlling the confinement regime by ECCD with high power launching in LHD

¹ National Institute for Fusion Science, 509-5292, Toki, Japan
² Research Institute for Applied Mechanics, Kyushu Univ. 816-8580, Kasuga, Japan
³ Department of Energy and Technology, Nagoya Univ. Nagoya 464-8463, Japan

Abstract

In the large helical device (LHD), fundamental electron cyclotron resonance heating (ECRH) by the electron Bernstein wave (EBW) excited via the ordinary-extraordinary–EBW (O-X-B) mode conversion process was performed with high power (~1MW) launching. Profiles of increase of the electron temperature (T_e) and the soft X-ray signals during the power injection suggest power absorption in the core region. Effects of the local modification of the rotational transform l/2π(=1/q) by electron cyclotron current drive (ECCD) on the formation and sustainment of the electron internal transport barrier (e-ITB) was investigated for the first time. Co ECCD raised l/2π close to 0.5 in the core region and caused the flattening of the T_e profile. Additional ECRH power is required to form the e-ITB. On the contrary, counter (cntr.) ECCD separates l/2π from 0.5 in the core region and avoids the flattening of the T_e profile. The e-ITB can be formed and sustained without additional ECRH. Analysis of the heat pulse transport with use of the modulation ECRH (MECH) shows the good confinement region extends to the l/2π =0.5 rational surface in the case of cntr. ECCD.