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

Experiments with a small amount of Ar puffed from the lower outer target into L-modeplasma in double null (DN), lower single null (LSN), and upper single null (USN)configurations studied the effects of magnetic configurations and the seeded locationrelative to the X-point on the performance of Ar seeding. With Ar seeded, the peak heatflux and the integrated power load onto the target decreased most significantly in the LSNconfiguration, although the increase of the line integrated radiation in the main plasmawas the lowest in this case and the highest in the USN configuration. The radiationfraction in the divertor rose from about 10% to 23% of the heating power in LSN, and fromaround 15% to 22% in DN, while it almost did not change in the USN configuration with Arseeding. The line emission of Ar XVI increased following the puff and then started todegrade 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 thepeaking of radiation in the core prior to the seeding in the LSN phase. Dedicate Modelingindicates that the LSN configuration has the highest divertor radiation fraction. Thehighest radiation from outside the divertor is in the USN configuration. With increasingAr seeding, the LSN configuration sees an increase of the radiation inside the divertorwhile in the USN configuration, it is the radiation from outside the divertor thatincreases most strongly. In the DN configuration, the radiation from both inside andoutside the divertor increases with seeding, with the former more strongly.