Speaker
Description
In tokamaks, intense heat fluxes strike the divertor targets, risking damage and core plasma contamination by eroded wall material. Future reactors must therefore operate in a detached regime, where heat loads and plasma temperatures near the walls are greatly reduced [1]. This can be achieved by impurity seeding, which promotes radiative cooling and momentum losses in the boundary plasma. However, minimizing impurity penetration into the core is critical to preserve fusion performance [2]. In this work, a lower single-null, L-mode, nitrogen seeded discharge on TCV is repeated while changing the seeding valve across six different poloidal locations, including private flux region (PRF), high-field side (HFS), low-field side (LFS) and ceiling (TOP). Results reveal that the access to a detached regime, diagnosed via divertor Langmuir probes and the CIII emissivity front, is mostly insensitive to the seeding location. On the contrary, core contamination (estimated via $Z_{eff}$) shows strongly different behaviors, especially when comparing PFR and TOP seeding, with the latter leading to $50$% higher $Z_{eff}$. Interestingly, HFS seeding from above the divertor baffle yields lower core contamination than LFS seeding from below the baffle, hinting at a potential role of flows in determining impurity redistribution. Bayesian inference is applied to multispectral visible imaging data [3,4] to infer 2D maps of nitrogen concentration in the divertor region and findings are compared to SOLPS simulations. These results highlight the potential to optimize seeding strategies and impurity content quantification for future devices.
[1] P C Stangeby 2018 PlasmaPhys.Control.Fusion 60 044022
[2] T. Pütterich et al 2019 Nucl.Fusion 59 056013
[3] A. Perek et al 2022 Nucl. Fusion 62 096012
[4] B.L. Linehan et al 2023 Nucl.Fusion 63 036021