High heat flux damage of the guard limiter in Heliotron E

We examined the limiter-plates of the side protectors of the ICRF antennae in Heliotron E at Kyoto University, which were damaged by high-heat-flux loading. The limiter plates were exposed to about 5000 discharges during one year of operation. The metallurgical examinations revealed that the heat flux had been more than 100 kW/cm² and about 2.5-8% of total plasma energy. The damaged area had been loaded with 100-160 kJ. It is estimated that 10²¹ manganese atoms were released into the plasma by this high-heat-flux damage of the limiter plates. The high-heat-flux damage generated cracks in the plates. Some of the cracks propagated into the unmelted parts. The damaged parts were found to contain a ferromagnetic phase.