Investigation of detachment in Double-Null configurations in the TCV tokamak.

Safe power exhaust in future fusion reactors will require, at the least, partially detached divertor operation. Alternative divertor configurations could facilitate access to such a regime. In particular, Double-Null (DN) configurations allow splitting most of the exhaust power between two outer legs and potentially reaching higher level of radiation thanks to the presence of two X-Points. In this work, we investigate the detachment on TCV in DN geometries with different outer leg positions, including a double Super-X configuration. Preliminary results show that detachment onset, as measured by the movement of the CIII front away from the targets, happens at lower density than in equivalent Lower Single-Null (LSN), while, for the same line-averaged density \textless ne\textgreater , a higher fraction (between 10{\%} and 50{\%}, depending on shape and \textless ne\textgreater ) of the input power is radiated. However, this enhanced accessibility of the detached regime appears to come at the price of a reduced detachment window. The double-null configurations disrupt at lower (between 10{\%} - 20{\%}) line-averaged densities than the equivalent LSN, after a quick movement of the CIII front towards the X-Point.