Radiation Loss and Impurity Abundance during ICRF Heating in the JIPP T-IIU Tokamak

Spectroscopic and bolometric measurements with spatial and temporal resolution show that large radiation loss brings about the decrease in electron and ion temperature and plasma energy. Regarding emissivity in a core plasma, the result by bolometric measurements well agrees with that estimated from impurity abundance and radiative cooling rates. Carbon limiters have an effect to suppress the radiation loss for Ohmic plasma, but is insufficient for ICRF heated plasma. The main contribution to radiation loss may be attributed to Fe impurity released from the ICRF antennae, the Faraday shield and vacuum vessel. By making carbonization, the Fe impurity is suppressed to a low level ( n Fe / n e ∼0.03%) and the radiation loss is reduced to P rad /( P OH + P fr )∼20%. This clearly supported by the observation of Z eff (3.9→1.2).