Assessment of drying status in KSTAR PFC cooling channels via transient temperature response analysis

This study assesses the post-drainage drying status of KSTAR Plasma Facing Components (PFC) Baking and Cooling (B&C) lines by analyzing transient temperature responses during the high-temperature nitrogen gas (GN 2 ) baking process. To this end, we analyzed the temperature trends of major PFCs, including the Tungsten Cassette Divertor (TCD). The results revealed that the thermal behaviors can be classified into two distinct modes based on the flow-path condition. First, the 'Blockage-first' mode, primarily observed in the Inboard Limiter (IL) and TCD, is characterized by an initial suppressed heating phase due to flow blockage caused by moisture traps, followed by a rapid jump indicating flow breakthrough. Second, the 'Open-first' mode, observed in other PFCs, exhibits transient evaporative cooling ( dT w /dt < 0) immediately after gas injection. These two modes provide practical thermal indicators for inferring local drying and flow-path conditions under the measurement constraints of the KSTAR PFC B&C system. Based on these findings, this study demonstrates a non-intrusive temperature-based approach for assessing drying status within the B&C lines relying solely on existing temperature measurements.