Simulation Study of Divertor Detachment Density Threshold in EAST

Full text: Divertor detachment is an effective and promising method to control the erosion and sputtering of divertor target materials for ITER and CFETR. It is necessary to achieve detachment at a relative lower upstream density to get a high current drive efficiency which is compatible with high duty cycle operations for ITER and CFETR. It is a significant work to find out what are the sensitive parameters and factors to affect the divertor detachment density threshold by modeling and experiment. In this work, we have studied the divertor detachment density threshold for L-mode discharge in EAST by using SOLPS code. The modeling results show that the suddenly increasing ratio of Dγ/Dα is in qualitative agreement with the experimental measurements on EAST when the particle flux landed on outer divertor target roll over. The effect of divertor closure on the threshold density has been investigated by modifying the location of the strike point at divertor target. The experimental and modeling results show that a good divertor closure is helpful for the capture of neutral particles to lower the density threshold of detachment. In additional, the predictive modeling works on the effect of plasma current (I_p) and the power across the scrape-off-layer (SOL) P_SOL on the detachment density threshold have been studied. We also find that the density threshold can be approximately scaled by P_SOL^5/7. Further work about the experimental validation of the predictive results will be carried out on EAST.