Actively cooled plasma-facing components and coolant removal system in KSTAR

This paper deals with the first commissioning of active cooling system and coolant removal system for plasma-facing components (PFCs). During 2015 KSTAR campaign, we have achieved a 55 s long pulse H-mode plasma operation. However, some plasma shots were terminated, not because of instabilities or limitation of heating power, but because of safety limit applied to the PFCs temperature: upper boundary to lock the system is 400 °C to protect the machine, and unlocked at 200 °C. In order to overcome this limitation and to achieve longer pulse, an active cooling system is installed. With the active cooling, the temperature of lower divertor is about 302 °C lower than that of upper divertor and returned quickly to initial temperature resulting in reduction of shot interval: Inertial cooling takes much longer time to unlock the safety inter-lock. One technical issue of this active cooling of PFCs is to remove coolant from the “cooling line”. The cooling line, pipe system inside the PFCs are also used to bake the PFCs. Therefore, a coolant removal system is assembled. The system is consists of adsorption dryer (external heater non purge air dryer), gas cooler, pipes and valve components. The coolant removal system was operated for 8 days during PFC baking operation period. The dew point of requirement value (<−40 °C) was decreased to −80 °C, and then PFC baking operation was well done. And we could be achieved a 70 s long pulse H-mode plasma at 2016 campaign.