Design of a PID controller for the pedestal top electron density at KSTAR*

The optimized electron density level is a key for achieving high confinement, detachment, and RMP-ELM suppression. Specifically, local density optimization at the pedestal is essential for advancing toward a core-edge integration solution. A recent KSTAR campaign report with a new tungsten divertor highlighted the challenges in attaining high confinement and RMP-ELM suppression, emphasizing the importance of local density control at the pedestal. We introduce our new pedestal top-density controller, which employs gas puff, supersonic molecular beam injection (SMBI), and resonant magnetic perturbation (RMP) as actuators. To facilitate real-time application, an artificial neural network accelerates the electron density profile reconstruction using the five channels of the two-colored interferometer (TCI). Our controller design is based on the plasma's gas response analysis from the 2023 campaign. This controller will undergo testing and further development during the 2024 KSTAR campaign. The developed controller is expected to facilitate the successful realization of hybrid and high-beta scenarios in the 2024 KSTAR campaign and to be integrated with the RMP-ELM and detachment controller in the 2025 KSTAR campaign.