Closed-loop control of the safety factor profile in the TCV tokamak

A key property that has a close relationship to both the performance and stability of the plasma in nuclear fusion tokamak devices is the safety factor profile (q-profile). As a result, extensive research has been conducted to develop algorithms to actively control the q-profile evolution with the goal of optimizing the tokamak approach to fusion energy production. The actuators that can be used to control the q-profile are the total plasma current, the auxiliary heating/current-drive system and the line-average electron density. In this work, we first investigate the effect that pure plasma auxiliary heating has on the q-profile in low performance (L-mode) operating scenarios in the TCV tokamak. This study indicates that pure auxiliary heating has a small effect on the q-profile in the examined scenarios. Therefore, feedback controllers that utilize the total plasma current and exclusively the auxiliary current-drive capabilities are designed for q-profile control in TCV. The controllers are designed to put emphasis on achieving the target q-profile in different spatial regions and to respond differently to errors in the q-profile. The control performance of each controller is tested with the simplified physics-based plasma profile simulation code RAPTOR. The comparison of the closed-loop performance of these controllers is done in preparation for future q-profile control experiments in the TCV tokamak.