Observation of the bulk ion density peaking in a discharge with an impurity hole in the LHD

Radial profiles of bulk ion and impurity ions density are simultaneously measured and quantified using charge exchange spectroscopy and peaking parameter, C_v. The peaking parameter is positive for inward and negative for outward convection in a plasma with an impurity hole in the Large Helical Device. Following the formation of an impurity hole associated with the transition from L-mode to ion ITB plasma, the bulk ion becomes peaked by the inward convection (C_v>0), while impurities (helium and carbon) become hollow due to the outward convection (C_v<0). In contrast to the ion ITB plasma, in the L-mode plasma the impurity profiles are peaked (C_v>0), where the bulk ion density profile remains flat (C_v∼0). Understanding of the impurity behavior in the ion ITB plasma could lead to a self cleaning plasma reactor concept, with an efficient impurity exhaust.