Control of tungsten impurity source and edge transport using different gas injection with full tungsten divertor on EAST

Abstract

Tungsten (W) erosion and edge transport are investigated for EAST L-mode discharges with different gas injection. It is found that W erosion can be suppressed or mitigated by Ne or D2 seeding when divertor detachment is achieved. Compared to edge D2 fueling, Ne seeding from the divertor target is favorable for full detachment condition and thus W erosion suppression. Increasing the upstream plasma density by edge D2 fueling can affect the divertor condition, which may lead to a W erosion mitigation. D2 puffing at divertor target is less effective on increasing the upstream plasma density than OMP D2 puffing, and thus it is less effective on reduction of W erosion rates. W gross erosion profiles with different amount of injected D2 at the divertor are reproduced by a mixed material W erosion model, which indicates that there exist a Li-C overlayer on the W surface of EAST divertor. Ne and D2 injection are also found to have different impact on the normalized core W density. For the attached divertor condition, divertor Ne seeding will increase W leakage, but a suitable D2 fueling from divertor target can strengthen the edge W screening. After the divertor detachment, although the W source is dramatically reduced, the W core density is kept in a high level for the Ne seeding discharges, and even increased for the D2 fueling discharges.