Characteristics of fast ions profile with MHD activities and improvement of fast ion confinement with AE suppression by counter ECCD in LHD

Characteristics of fast ion profile with MHD activities have been investigated in LHD deuterium experiments. The beam deposition profiles are changed by means of the selection of the operational ion source in tangential NBIs. Two ion sources are mounted on tangential NBIs with different tangential radius, therefore, the combination of ion sources operation and plasma position control enables us to change the beam deposition profiles in LHD plasmas. The demonstration of fast ion profile control without any Alfven eigenmode (AE) activity (V_fastion < V_Alfven/3) was carried out. Qualitative agreement of neutron emission profile was obtained between the numerical calculation (GNET code) and the experimental observation with the vertical neutron camera (VNC). In the case of existing MHD activity (V_fastion > V_Alfven/3), two types of characteristic of fast ion profiles were identified depending on the bulk plasma density. In low density regime, experimentally observed fast ion profiles are independent of the beam deposition profile, which is very similar to the profile stiffness observed in DIII-D plasmas and in a hybrid simulation. On the other hand, in the high density regime, the fast ion profile changes depending on the beam deposition profile.