The double-peaked distribution of particle deposition at divertor targets has been observed in various tokamaks, and is considered a potential approach for mitigating divertor particles and heat load in future fusion reactors. Recently, the systematical analysis of the double-peaked distribution behavior during EAST experiments shows that the appearance of the double-peaked profile is related to the line-average density and heating power. In order to understand general trends and related mechanisms, the influences of the upstream density (ne,sep) and power in the scrape-off layer (PSOL) on the double-peaked density profile are investigated by SOLPS-ITER simulations with full drifts and currents. It is found that the ne peak near the strike point is mainly contributed by the strong ionization source close to the target, and the ne peak in the far-SOL region is caused by the synergetic effects of poloidal and radial E × B drifts along the SOL. The double-peaked distribution is affected by the PSOL and impurity seeding by increasing or decreasing the whole profile of the electron temperature at the target (Tet). When the peak value of Tet (Tet,peak) is fixed, the density peak in the far-SOL is increased for higher ne,sep by reducing the Tet in the far-SOL region on the lower-field side under unfavorable BT and by the upstream-extended ionization source due to the geometry effect on the high-field side under favorable BT. Statistical analysis of the simulated results shows that the scaling expression of the peak ratio is ∼. In addition to the upper boundary found in the analysis of EAST experiments, a lower boundary of the region where the double-peaked feature appears on the PSOL-ne,sep plane is identified by simulations and preliminarily confirmed according to the measurements in several EAST discharges.
SOLPS-ITER modeling of SOL-divertor plasmas with different configurations in EAST