Modeling study of the onset density for divertor detachment on EAST

The onset density of detachment for L-mode discharges on Experimental Advanced Superconductiong Tokamamak has been studied using the SOLPS code. The effect of divertor closure on the onset density has been assessed by modifying the location of the strike point on a divertor plate. The modeling shows qualitative agreement with experiments in the density threshold. It is found that increasing divertor closure by moving the strike point close to the “V” corner can effectively trap neutrals in a localized region near the plasma strike point and then lower the density threshold of detachment. The influence of plasma current (Ip) on the onset density has also been investigated. The simulation shows that with Ip increased, divertor detachment was achieved at a relatively low normalized density due to the increase in Greenwald density (nG). In addition, the effect of the power across the scrape-off-layer (PSOL) and the radiation fraction on the detachment density threshold has also been studied. The detachment density increases significantly with PSOL as expected, and it can be approximately scaled by PSOL5/7, which is in accordance with the basic two-point model. It is also found that the detachment density can be reduced remarkably through increasing impurity radiative loss.