Enhancements in Vertical Instability Control for the HL-3 Tokamak

Vertical position control of tokamak plasmas is essential for exploring operational limits and ensuring stable operation at high elongations to avoid disruptions. This study focuses on improving vertical instability control in the HL-3 tokamak by enhancing the signal-to-noise ratio of control signals and optimizing control strategies. We employed improved diagnostic techniques using Mirnov coils and flux loops, combined with digital filtering technology, to mitigate the effects of power supply switching and measurement noise. The vertical stabilization (VS) control system was upgraded with an optimized low-pass filter for vertical position estimation, a novel method for vertical velocity estimation using direct voltage signals from diagnostics, and an improved control algorithm. These enhancements resulted in significant improvements in control precision and noise reduction. Experimental results demonstrated successful control of highly elongated plasmas ( \(\kappa \) $\kappa$ up to 1.8) with high plasma currents (up to 1.6 MA), achieving vertical position control accuracy better than 1 cm during the plasma current ramp-up phase. These advancements expand the operational parameter space of HL-3, paving the way for higher performance plasma operation.