Experiments and SOLEDGE3X modeling of dissipative divertor and X-point Radiator regimes in WEST

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. • X-point radiator regimes experiments have been run in the WEST tokamak. • XPR plasmas were controlled with an interferometry signal at the X-point. • The XPR transition in WEST is abrupt, from hot to cold & dense divertor plasma. • The divertor target plasma becomes dense, and does not detach upon transition. • SOLEDGE3X modeling showed a XPR stabilizing mechanism remains to be identified. • This stabilizing effect may result from a dynamics effect, or impurity mix. • These observations highlight the need for core–edge integrated modeling.