[en] Radiative divertor experiments with Ar and Ne seeding have been carried out during recent EAST experimental campaigns. The results proved the high efficiency of Ar and Ne in reducing heat load and particle flux onto the divertor target. However, core plasma contamination and PFCs sputtering were observed with Ar seeding especially when the impurity was seeded from upper tungsten divertor. The experiments with different seeding pulse width proved Ar is a strong radiator for EAST, and excessive Ar seeding easily caused the burst of radiation in the plasma core region which led to a great loss of plasma stored energy. To compare with Ar seeding, Ne seeding experiment was carried out in EAST 2016 spring campaign. Its preliminary results showed Ne, compared with Ar, has advantages on radiation profile and less contamination in plasma core region. (author)

[en] Increasing the density in a tokamak is limited by the so-called density limit, which is generally performed as an appearance of disruption causing loss of plasma confinement, or a degradation of high confinement mode which could further lead to a H  →  L transition. The L-mode and H-mode density limit has been investigated in EAST tokamak. Experimental results suggest that density limits could be triggered by either edge cooling or excessive central radiation. The L-mode density limit disruption is generally triggered by edge cooling, which leads to the current profile shrinkage and then destabilizes a 2/1 tearing mode, ultimately resulting in a disruption. The L-mode density limit scaling agrees well with the Greenwald limit in EAST. The observed H-mode density limit in EAST is an operational-space limit with a value of $0.8\sim <!--\; ???\; -->0.9n_{\text{GW}}$. High density H-mode heated by neutral beam injection (NBI) and lower hybrid current drive (LHCD) are analyzed, respectively. The constancy of the edge density gradients in H-mode indicates a critical limit caused perhaps by e.g. ballooning induced transport. The maximum density is accessed at the H  →  L transition which is generally caused by the excessive core radiation due to high Z impurities (Fe, Cu). Operating at a high density ($>2.8\times <!--\; ??\; -->{10}^{19}{\text{m}}^{-<!--\; ???\; -->3}$) is favorable for suppressing the beam shine through NBI. High density H-mode up to $5.3\times <!--\; ??\; -->{10}^{19}{\text{m}}^{-<!--\; ???\; -->3}(\sim <!--\; ???\; -->0.8n_{\text{GW}})$ could be sustained by 2 MW 4.6 GHz LHCD alone, and its current drive efficiency is studied. Statistics show that good control of impurities and recycling facilitate high density operation. With careful control of these factors, high density up to 0.93$n_{\text{GW}}$ stable H-mode operation was carried out heated by 1.7 MW LHCD and 1.9 MW ion cyclotron resonance heating with supersonic molecular beam injection fueling. (paper)

[en] A critical issue for ITER and future fusion devices is the handling of excessive heat load. It will require a high radiation level for power exhaust to avoid divertor heat overload and excessive surface erosion rates. Increasing divertor radiation by injecting impurities is a general and effective method to reduce scrape-off layer heat flux and to cool the divertor plasma to detachment. In recent years, argon (Ar) and neon (Ne) have been widely used in radiative divertor experiments on EAST and other devices. To compare effects of these two impurities and understand well the radiative divertor physics, both experiment and simulation work of Ar and Ne seeded plasma are carried out simultaneously in EAST.