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X-Point Radiator (XPR) regimes have been obtained in WEST tokamak experiments with nitrogen seeding during the experimental campaigns of 2023 and 2024. These experiments showed the formation of a stable toroidal radiating ring near the X-point, similar to observations in other devices such as JET, ASDEX-Upgrade, TCV, and COMPASS. In WEST, the onset of this regime is associated with a sharp transition of the divertor plasma from hot to cold and dense conditions, with increased particle fluxes, indicating that the plasma is not detached. At the same time, core conditions are significantly improved. These scenarios were successfully controlled in WEST using an interferometry line-of-sight passing through the X-point. Interpretative modeling of these discharges with the SOLEDGE3X-EIRENE code reveals that a physics mechanism needed to stabilize WEST nitrogen XPRs is not present when driving the simulations at constant power. On the contrary, a stable XPR can be obtained by increasing the power injected at the time of the XPR onset to represent the reduction of W contamination, highlighting the need to describe the plasma dynamics and go toward integrated core–edge simulations.

The X-point radiator (XPR) is an attractive scenario that may contribute to solving the power exhaust problem in future fusion devices. The 2D transport code SOLPS-ITER was applied to reproduce the experimentally measured plasma condition with an XPR in the ASDEX Upgrade tokamak and to compare with a reduced model. Neutrals penetrating from the adjoining cold divertor region and the large connection length near the X-point play an important role in initiating an XPR. However, once such a radiator is created, it persists even if the fueling and impurity seeding rates were reduced. The redistribution of plasma density and radiation near the X-point caused by fluid drifts at the XPR was studied in the simulation. [ABSTRACT FROM AUTHOR]

The X-point radiator (XPR) is an attractive scenario that may contribute to solving the power exhaust problem in future fusion devices. The 2D transport code SOLPS-ITER was applied to reproduce the experimentally measured plasma condition with an XPR in the ASDEX Upgrade tokamak and to compare with a reduced model. Neutrals penetrating from the adjoining cold divertor region and the large connection length near the X-point play an important role in initiating an XPR. However, once such a radiator is created, it persists even if the fueling and impurity seeding rates were reduced. The redistribution of plasma density and radiation near the X-point caused by fluid drifts at the XPR was studied in the simulation.