Control and operation of the gas injection systems for KSTAR tokamak

Several gas injection systems such as fueling, massive gas injection (MGI), supersonic molecular beam injection (SMBI) have been installed for the Korea Superconducting Tokamak Advanced Research (KSTAR). Piezoelectric valves with a built-in piezoelectric plate of disc-bender type were used for the precise feedback control of gas flow. The relationship between the displacement and blocking force of the piezoelectric plates is taken into account in designing and fabricating piezoelectric valves. The MGI system was installed for the mitigation of plasma disruption. The MGI valve is composed of two-volume chamber. The valve is equipped with an aluminum piston and an actuator coil of inductance 0.1 mH. The power supply unit using a capacitor discharge method has been developed in order to drive the MGI valve. The SMBI system consisting of LN2 cooling line, pulse valve, and its controller was operated for the mitigation of edge localized mode (ELM). The LN2 cooling line is used to increase the density of the injected gas. The status and specification of each gas injection system is presented and the operational characteristics are analyzed.