Speaker
Description
Understanding and quantifying particle and energy transport at the boundary, detachment and its stability in the divertor region, is crucial for magnetic confinement fusion, as this determines both plasma performance and target loads. For this reason, several fast helium beam systems, based on the ASDEX Upgrade (AUG) midplane system [1], have been installed in the divertors of AUG [2] and Wendelstein 7-X (W7-X). These diagnostics allow the investigation of edge transport processes, such as modes and filaments, with high spatiotemporal resolution in both $n_\text{e}$ and $T_\text{e}$ [3] as well as detachment phenomena in the divertor [4]. With the new possibility of measuring highly temporally resolved 1D profiles, we observe strong variations (\textasciitilde 50\% relative fluctuation amplitude in $T_\text{e}$ and $n_\text{e}$) and movements of the radiation front in the divertor region of W7-X. These events change transiently the plasma state for \mbox{1--20 ms} with transition durations from \mbox{0.5--2 ms}. Since such a diagnostic is placed in two divertors of W7-X, the toroidal and poloidal correlation of these events is investigated, along with other diagnostics. This contribution explores the physical nature of these events and their influence on the target heat flux due to the strong $T_\text{e}$ and $n_\text{e}$ variations. These investigations are carried out for different magnetic configurations and plasma parameters. Furthermore, the measurements will be compared with similar events observed by the same diagnostic at AUG. This presentation aims at a better understanding of detachment on fast timescales in \mbox{W7-X}, the influence of fast events on the divertor island region, and it classifies the phenomena in relation to the tokamak divertor.
[1] Michael Griener et al. 2018 Rev. Sci. Instrum. 89, 10D102
[2] Sebastian Hörmann et al. 2024 Rev. Sci. Instrum. 95, 113507
[3] Joey Kalis et al. 2024 Nucl. Fusion 64, 016038
[4] Sebastian Hörmann et al. 2025 Plasma Phys. Control. Fusion 67 075016