Description
The successful operation of future fusion reactors relies on achieving control of the plasma throughout the discharge. While this constitutes a major scientific challenge, it is also essential for ensuring reactor safety, reliability and optimal performance. Advanced control schemes are currently under development for this purpose, with ASDEX Upgrade (AUG) playing a central role.
As part of these advancements, in early 2025 we started implementing real-time spectroscopy measurements for the first time at AUG. The use of spectroscopy for plasma control is a key step toward developing reactor-relevant strategies, as it is likely one of the few diagnostics capable of withstanding reactor-like conditions [1].
Although a full online demonstration is still pending, the real-time data acquisition is now operational and fully integrated within AUG’s Discharge Control System [2]. This implementation can be applied to both charge exchange recombination spectroscopy and divertor spectroscopy. By the 2026 experimental campaign, we aim to implement a full offline demonstration of the real-time analysis capabilities, to be subsequently tested with dedicated discharges.
A wide range of phenomena can potentially be controlled using spectroscopy. We will focus on plasma exhaust, a critical issue for reliable reactor operation, monitoring the temperature at the strike point, i.e. the detachment process, via line ratios of Deuterium [3] and Helium [4] emissions. Reactor-relevant lines of sight, such as those starting from the mid-plane ports, will be used [5]. In addition, we intend to exploit spectroscopic measurements to control the plasma fuelling composition [6], namely the Hydrogen-to-Deuterium density ratio, derived from divertor spectroscopy, especially during ICRH experiments.
A detailed description of the real-time approach will be presented, including a critical assessment of its limitations and potentialities, based on the offline results. Depending on the experimental campaign progress, the first online results may also be shown, along with a discussion of the performance of the new control strategies.
[1] Biel et al., Fusion Eng. Des., 2022
[2] Treutterer et al., Fusion Eng. Des., 2014
[3] Rikala et al., Nucl. Mater. Energy, 2025
[4] Griener et al., PPCF, 2017
[5] Raukema et al., Fusion Eng. Des., 2024
[6] Lennholm et al., PRX Energy, 2025