Unlocking Plasma Secrets: Probing the Electron Temperature Profile Across the Separatrix
In a tokamak, the temperature profile across the separatrix is often described by a single decay length although parallel heat transport opens a new heat loss channel on the open field lines
In a tokamak, the temperature profile across the separatrix is often described by a single decay length although parallel heat transport opens a new heat loss channel on the open field lines. But not only parallel transport is different, also perpendicular transport could change across the separatrix. By using the thermal helium beam diagnostic on ASDEX Upgrade in combination with the Bayesian IDE equilibrium with edge pressure gradient constraint, we studied the electron temperature profile around the separatrix in both L-mode and H-mode discharges. The temperature decay length was found to vary radially around the separatrix rather than following a simple exponential decay (see figure). In H-mode, it is shorter in the confined region and longer in the near scrape-off layer. Therefore, the maximum curvature in the electron temperature profile aligns with the separatrix position. Our findings demonstrate that by measuring electron temperature profiles using the thermal helium beam diagnostic, we can determine the separatrix position reliab
published in: S. D. Esteban, M. Griener, E. Wolfrum, et al., Plasma Physics and Controlled Fusion 66, 015011 (2024)