Comparative modeling studies of carbon and tungsten impurity transport in the boundary plasma of EAST with a partially detached divertor condition

Abstract

• The main pathways of impurity leakage from tokamak divertor target to the core plasma are illustrated by dedicated modeling. • The key physics governing impurity screenings under both attached and detached plasma conditions are clarified. • The low-Z C and high-Z W impurities have different transport properties especially under the attached divertor plasma conditions. • Both the impurity source distribution and the divertor plasma condition have great impact on the edge transport of C and W. The source and leakage of both C and W are comparatively studied for a partially detached divertor operation condition on EAST. Based on the EAST experiments, sequential SOLPS-DIVIMP simulations are carried out to study the transport of intrinsic impurities in the boundary plasma. Carbon distribution from the fluid SOLPS simulation is in good agreement with the impurity tracing results from the Monte-Carlo DIVIMP simulation. The impurity leakage processes from the divertor target to the core plasma are quantitatively analyzed and divided into three parts: the prompt redeposition, the divertor screening, and the main SOL screening. Under the partially detached divertor condition, W has a higher prompt redeposition rate and a weaker cross-field transport from the main SOL to the core region than C. However, the strong parallel impurity transport from the divertor region to the main SOL makes the total leakage rate of W two times higher than that of C. The impurity velocity gained from the ion temperature gradient force in both the near-SOL detached region and the far-SOL attached region is evaluated. The relatively higher ion temperature gradient velocity of W in the attached region is the main reason for the higher divertor leakage rate than C, and the strong W source in the far-SOL makes the leakage from the attached region more significant.