Speaker
Description
Future fusion reactors will differ significantly from current fusion devices, particularly in that diagnostics will serve exclusively plasma control functions [1]. These diagnostics must operate with high reliability under conditions far harsher than those found, for example, in ITER. The DEMO environment demands novel design solutions for nearly all diagnostics, even though experimental data on material behavior under the expected radiation doses remains limited.
The challenges can be illustrated through the example of the development of an optical divertor monitoring diagnostic system, which includes the detachment control [2]. The diagnostic capabilities are developed to meet the requirements of the plasma control system [1]. A key question for the conceptual design of the detachment control branch is whether a relatively simple signal can be identified that reliably indicates the detachment. Based on previous JET experimental results [3] the ratios of various Hydrogen and Helium emission lines in the visible spectrum were identified as possible candidates based on SOLPS-ITER simulations [4].
Optical diagnostics are planned for installation in the equatorial ports of DEMO. The extremely harsh environment and high reliability requirements necessitate specialized optical and opto-mechanical solutions. The first mirrors are exposed to continuous impurity fluxes from the plasma, leading to erosion and deposition on the mirror surface. Deuterium-filled ducts, for example, can mitigate damage from high-energy charge-exchange neutrals, and a novel opto-mechanical design has been proposed [5] to enhance the lifetime and optical performance of the first mirror. For the first time, ERO2.0 simulations - including the release and transport of sputtered iron particles from the duct walls - have been performed in a realistic diagnostic geometry to predict erosion and deposition on the first mirror. The presented methodology can be generalized and transferred to other optical diagnostics in DEMO or similar fusion power plants.
Keywords: EU-DEMO; Diagnostics; Spectroscopy, Detachment
[1] W. Biel et al. 2022 Fusion Engineering and Design Volume 179, 113122
[2] D. Dunai et al. 2024 33rd Symposium on Fusion Technology, Dublin
[3] A.G. Meigs et al. 2013 Journal of Nuclear Materials 438 S607–S611
[4] F. Subba et al 2021 Nucl. Fusion 61 106013
[5] I. Katona et al. 2025 Fusion Engineering and Design Volume 219, 115292
