Comparison of ion internal transport barrier formation between hydrogen and helium dominated plasmas

Ion internal transport barrier (ITB) was formed in both hydrogen discharge and helium dominated discharge. The central ion temperature was investigated as a function of the hydrogen density ratio (nH/(nH+nHe)). The central ion temperature increases with the decrease of the hydrogen density ratio, while the electron temperature does not change significantly. The experimentally observed ion temperature was not reproduced by the prediction of TASK-3D modeling. The dominant activity in the density fluctuation measured by the phase contrast imaging is consistent with ion temperature gradient mode and they are almost identical between the hydrogen dominated and helium dominated plasmas.