Speaker
Description
The electron temperature (T$_{e,sep}$) and density (n$_{e,sep}$) at the separatrix at the outboard midplane (OMP) are the key parameters in mapping the operational space for power exhaust handling in tokamak fusion devices. Here, three methods of determining the Te,sep and ne,sep in ST40 are compared. First is through the reverse two-point modeling [1], wherein the electron temperature (T$_{e,target}$) and density (n$_{e,target}$) at the outer divertor from Langmuir probe measurements are used to predict the upstream parameters at the OMP. Secondly, available T$_{e,sep}$ and n$_{e,sep}$, from Thomson scattering data are used. Both methods will use the separatrix location given by EFIT during the calculation. Lastly, the Heat flux Engineering and Anaysis Toolkit (HEAT) [2] and IR data are used to determine the correction factor of the separatrix location calculated from the difference of the simulated and experimental heat flux peak locations. The upstream parameters are then employed to predict the operational space for power exhaust handling in ST40 using the separatrix operational space framework (SepOS) [3]. Initial results showed that observed periods of enhanced plasma stored energy and reduced D-alpha emissions are consistent with an H-mode phase, given their SepOS parameters. The results will be used to determine whether the parameters from ST40, a compact high-field spherical tokamak, are comparable with published normalized multi-machine SepOS database.
[1] J H Nichols et. al, Plasma Phys. Control. Fusion 66 (2024) 045013.
[2] EJC Tinacba et. al., Nuclear Materials and Energy 41 (2024) 101791.
[3] T Eich et al., Nuclear Materials and Energy 42 (2025) 101896.