SOLPS-ITER simulation of an X-point radiator in TCV

TL;DR

This study uses SOLPS-ITER simulations to analyze the formation of an X-point radiator in nitrogen-seeded TCV experiments, revealing how nitrogen seeding influences power dissipation, impurity radiation, and divertor behavior in fusion devices.

Contribution

It provides the first detailed simulation-based analysis of the X-point radiator regime in nitrogen-seeded TCV, including effects of divertor geometry and impurity radiation dynamics.

Findings

Over 90% of input power dissipated in XPR region.

Nitrogen seeding moves ionization front away from target, aiding cooling.

Baffled divertor geometry enhances access to XPR regime.

Abstract

SOLPS-ITER simulation is performed to reproduce the X-point radiator recently observed in nitrogen-seeded TCV experiments, which is a scenario that may be favorable to solve the power exhaust problems in future fusion devices. The simulations reveal the transition from the detached regime without XPR to the XPR regime, when increasing the nitrogen seeding rate. A cold X-point core surrounded by ionizing and radiative mentals is formed inside the separatrix and slightly above the X-point, where more than 90% of the total input power is dissipated. The cold X-point core exhibits a temperature of approximately 1eV and features high recombination rate to host the convective fluxes from the ionizing mental. Increasing nitrogen seeding rate also moves the nitrogen ionization front away from the target faster than the nitrogen stagnation point, which enhances the divertor nitrogen leakage to the main chamber and benefits the XPR region cooling. Carbon radiation decreases as the nitrogen seeding increases, and carbon radiation contributes to above 5% of the core impurity radiation before entering the XPR, which decreases to 2.8% when reaching the XPR. Both baffled and unbaffled divertor geometries are simulated and compared, showing that baffles facilitate the access to XPR by increasing the X-point neutral density, but requires higher seeding rate to enter the XPR regime.