X-Point Target Radiator Regime in Tokamak Divertor Plasmas.

Fusion plasma regimes with a strongly radiating magnetic X point are promising candidates to tackle the outstanding power exhaust challenge in reactor-scale devices. In this Letter, we report on a new type of X-point radiator, the XPTR (X-point target radiator), produced by a secondary X point placed well away from the confined plasma. This XPTR features strongly facilitated detachment access and significantly reduced sensitivity of the radiative front position near the secondary X point. Consistent with a reduced analytical model, the physical origin of X-point radiation is rooted in its magnetic geometry, irrespective of whether the field lines are closed or open. The results presented open up a class of novel power exhaust concepts where radiative edge cooling can be robustly avoided during divertor detachment.