Overview of SOL transport and detachment in alternative divertor geometries on TCV

The flexibility of the TCV magnetic geometry and its open divertor allow the exploration, in a single machine, of the whole zoo of alternative divertor geometries. In dedicated L-mode scans, divertor leg length, poloidal flux expansion, and target radius have been varied and additional X-points have been introduced near the core plasma and near the target. Experiments in attached conditions reveal that the heat flux width λ_q, inferred from target infrared thermography and Langmuir probe measurements, increases with divertor leg length and is weakly dependent on poloidal flux expansion. The effectiveness of divertor cross-field transport in reducing parallel heat fluxes at the target is found to decrease significantly with increasing poloidal flux expansion, as parameterized by the divertor spreading factor S. The density threshold to detach the outer leg decreases with increasing divertor leg length, consistent with the observed increase in λ_q, but is otherwise fairly insensitive to geometrical modifications such as poloidal flux expansion and target radius.