Vertical instability studies and novel real-time metrics applications for proximity controller development in the TCV and DIII-D tokamaks

Controlling plasma position and shape is crucial for achieving high performance in tokamak fusion plasmas. Vertical position control is especially important for elongated plasmas to avoid vertical displacement events (VDEs), which can disrupt the plasma and damage tokamak components. A proximity controller based on real-time growth rate estimation has been implemented on the TCV tokamak. This controller monitors the plasma growth rate to maintain stability, using the RZIp model (similar to [Olofsson 2022 PPCF 64 072001]), which is fast enough for online implementation. Initially, the actuators included a simple radial controller (part of SAMONE [T. Vu et al. 2021 IEEE 68.8]) and the newly implemented TCV shape controller. Additionally, a new metric, the maximum controllable displacement [D. Humphreys et al. 2009 Nucl. Fus. 49 11], has been studied and implemented in real-time at both TCV and DIII-D. This metric is being considered as a potential replacement for growth rate estimation in the proximity control loop, as it may better assess the controllability of the plasma's vertical position by incorporating key features of the plasma magnetic control system for vertical stabilization.