Investigation of the effects of impurity seeding under different magnetic configurations in L-mode plasma in EAST tokamak

Experiments with a small amount of Ar puffed from the lower outer target into L-mode plasma in double null (DN), lower single null (LSN), and upper single null (USN) configurations studied the effects of magnetic configurations and the seeded location relative to the X-point on the performance of Ar seeding. With Ar seeded, the peak heat flux and the integrated power load onto the target decreased most significantly in the LSN configuration, although the increase of the line integrated radiation in the main plasma was the lowest in this case and the highest in the USN configuration. The radiation fraction in the divertor rose from about 10% to 23% of the heating power in LSN, and from around 15% to 22% in DN, while it almost did not change in the USN configuration with Ar seeding. The line emission of Ar XVI increased following the puff and then started to degrade near the end of LSN and USN phases. No such degradation was seen in the DN phase, meaning that some Ar dwelt in the core till the LSN phase began, which explained the peaking of radiation in the core prior to the seeding in the LSN phase. Dedicate Modeling indicates that the LSN configuration has the highest divertor radiation fraction. The highest radiation from outside the divertor is in the USN configuration. With increasing Ar seeding, the LSN configuration sees an increase of the radiation inside the divertor while in the USN configuration, it is the radiation from outside the divertor that increases most strongly. In the DN configuration, the radiation from both inside and outside the divertor increases with seeding, with the former more strongly.