Progress on Real-time Density Control Capability of the KSTAR Tokamak

J.-W. Juhn, (V. Graber, H. Al Khawaldeh, S. T. Paruchuri, E. Schuster), et al. (Collaboration Paper)

30th IAEA Fusion Energy Conference

Chengdu, China, October 13-18, 2025

Abstract

For more than a decade, the density control capability of the KSTAR tokamak has been improved continuously to present both in diagnostics and in control knobs: from the beginning of the KSTAR tokamak, a single-channel 280 GHz radial millimeter-wave interferometer (MMWI) works with its particular phase comparator that could deliver real-time analog output signals to the plasma control system (PCS). For the H-mode target plasmas, 2.52 THz vertical single-channel far infrared interferometer (FIRI) takes its role achieving more than 50 s of long-pulse H-mode plasma density control. It has been followed by a tangential 5-chord two-color interferometer (TCI) whose wavelengths are 10.6 µm and 660 nm respectively, for the vibration noise cancellation. The latest TCI is equipped with a full digital phase comparators(DPCs) providing high bandwidth digital density signals of all five chords directly to the PCS. The density profile control also needs effective multiple actuators for realizations. In addition to the fast gas injection systems (FGI) by gas puffing, a supersonic molecular beam injector (SMBI) and pellet injection system (PIS) are ready and tested in feedback loop respectively. SMBI could increase H- mode density more effectively than gas puffs. PIS also demonstrated its working on H-mode density control for the first time in KSTAR with more than 30% of fueling efficiencies. All the diagnostic-actuator sets worked as single-input-single-output (SISO) up to date but they are ready to work as being assembled for multi-input-multi-output(MIMO) control as well as for the advanced control schemes.