Design and operation results of nitrogen gas baking system for KSTAR plasma facing components

• Vacuum pressure in a vacuum vessel arrived at 7.24 × 10−8 mbar.
• PFC temperature was reached maximum 250 °C by gas temperature at 300 °C.
• PFC inlet gas temperature was changed 5 °C per hour during rising and falling.
• PFC gas balancing was made temperature difference among them below 8.3 °C.
• System has a pre-cooler and a three-way valve to save operation energy.

A baking system for the Korea Superconducting Tokamak Advanced Research (KSTAR) plasma facing components (PFCs) is designed and operated to achieve vacuum pressure below 5 × 10−7 mbar in vacuum vessel with removing impurities. The purpose of this research is to prevent the fracture of PFC because of thermal stress during baking the PFC, and to accomplish stable operation of the baking system with the minimum life cycle cost. The uniformity of PFC temperature in each sector was investigated, when the supply gas temperature was varied by 5 °C per hour using a heater and the three-way valve at the outlet of a compressor. The alternative of the pipe expansion owing to hot gas and the cage configuration of the three-way valve were also studied. During the fourth campaign of the KSTAR in 2011, nitrogen gas temperature rose up to 300 °C, PFC temperature reached at 250 °C, the temperature difference among PFCs was maintained at below 8.3 °C, and vacuum pressure of up to 7.24 × 10−8 mbar was achieved inside the vacuum vessel.