Study Of The Edge Transport In The J-TEXT Tokamak During Ohmic Discharge With A High Field Side Single-null Divertor Configuration

During the operation of the tokamak,with the continuous improvement of parameters,the interaction between the edge plasma and the plasma facing components enhances,and the heat load of the first wall is increased.In order to alleviate the heat load of the first wall,further improve the plasma operation parameters and improve the ability of impurity removal,the divertor configuration is widely used in tokamak device.The divertor configuration improves the plasma operation parameters,and effectively confines interaction between the edge plasma and the plasma facing components.Meanwhile,the screening ability of impurities improves,and the ability of removing reactive impurities enhances.The edge plasma transport in the divertor configuration not only affects the interaction between the plasma and the plasma facing components,but also is crucial to the core confinement.The discharge in the high field side divertor configuration has been successfully carried out in J-TEXT,which shows its advantages in improving the operation parameters and reducing the impurity diffusion.In addition,it is planned to introduce the magnetic island divertor configuration into the J-TEXT for further exploration.The research on the edge plasma transport in the high field side divertor configuration is helpful to further understand the transport characteristics of divertor configuration and explore its influence factors.This article includes the first experiments on the edge plasma transport in the high field side（HFS）midplane single-null divertor configuration on J-TEXT during ohmic discharge.In these experiments,by fixing the plasma current and changing the divertor coil current,the influence of the X-point location on the edge plasma transport has been explored.When the divertor coil current drops to 8 k A,the X-point moves behind the target,so that the plasma returns to the limiter configuration.The central channel line-average density drops from6.49×10¹⁹ m^-3 to 2.73×10¹⁹ m^-3.The corresponding Greenwald fraction drops from0.79 to 0.50.With 15 k A divertor coil current,when the central channel line-average density increases from～4×10¹⁹ m^-3 to～6.8×10¹⁹ m^-3,the peaking factor(ratio of the central channel line-average density to the edge density （?）_e/n_e,edgeincreases by about 40%,and the edge electron temperature decreases from about 35 e V to about 27 e V.Moreover,the growth rate of the ion saturation flux in downstream target is faster than that in upstream.In the HFS midplane single-null divertor configuration,when the divertor coil current is 15 k A and 12 k A,with the increase of plasma density,the central channel density normalized radiation intensity（AXUV and SXR）decreases by more than 50%,and the CIII radiation peak gradually moves from the SOL to the inner side of the X-point,and then to the core.In order to better understand the physics behind the experiments,EMC3-EIRENE（3D edge Monte Carlo code coupled EIRENE）was first applied to the simulation of the edge plasma transport in the high field side midplane single-null divertor configuration on J-TEXT.The particle cross-field transport coefficient D_⊥,the energy cross-field transport coefficient X_⊥,the electron density at the separatrix n_e,sep and the power entering the scrape-off layer（SOL）_SOLare determined by fitting the electron density and the electron temperature distribution measured by the reciprocating probe（RP）.And the radiation diagnostic results are involved.Through the simulations,the two-dimensional distribution is obtained,which is helpful to better observe the changes of plasma and impurity distribution with the X-point displacement.In the simulation,the power flux decay length decreases from 4.6 cm to 3.3 cm as the X-point moves far away from the target.Meanwhile,the impurity screening of the SOL enhances.Therefore,the edge plasma transport is affected by the X-point location and the plasma density in the HFS midplane single-null divertor configuration on J-TEXT.As the X-point moves far away from the target,the plasma operation parameters further improve and the impurity screening enhances.With the increase of the plasma density,the edge temperature decreases,the target particle flux increases rapidly,and the impurity radiation increases.