Comparison of divertor behavior and plasma confinement between argon and neon seeding in EAST

The exhaust of excessively high heat and particle fluxes on the divertor target is crucial for EAST long-pulse operation. In the recent EAST experiments, stable partial energy detachment around the upper outer strike point with H98,y2 ~ 1 was achieved with either Ne or Ar seeding from the upper outer divetor target in the upper single null configuration with ITER-like tungsten divertor. With either Ar or Ne seeding, the electron temperature around the upper outer strike point (Tet,UOSP) was maintained at around 5 eV, the peak temperature of divertor target surface around the upper outer strike point (Tdiv,UO) decreased significantly, and material sputtering was well suppressed. It was observed that there was less Ar seeding needed for partial energy detachment onset than Ne seeding, which shows that Ar is more efficient in the cooling of Tet on the upper outer divertor than Ne. However, there was no detachment on the upper inner divertor with Tet around strike point (Tet,UISP) remaining > 10 eV with either Ar or Ne seeding from the upper outer divertor. Accompanied with the disappearance of double peak phenomenon of ion flux density on the upper inner divertor target (js,UI), the peak Tdiv,UI around the strike point increased to around 300 ℃. Although the heat flux on the upper inner divertor target (qt,UI) is still in the acceptable level, either Ar or Ne seeding only from the upper outer divertor target is not enough to protect the upper inner divertor target from sputtering under current EAST conditions. On the other hand, Ar seeding always causes confinement degradation in the partial energy detachment state. It was observed that there is a slight confinement improvement (~10%) with Ne seeding, which may be due to density peaking, dilution effects and stabilization of the ion temperature gradient (ITG) mode.