A conventional single null divertor geometry has been proposed for Chinese fusion engineering testing reactor (CFETR) with fusion power up to gigawatt level. Modeling using the SOLPS5.0 code package shows promising results for divertor power exhaust by seeding with neon (Ne) and deuterium (D2). Partial detachment for both inner and outer divertor targets can be achieved with a peak heat load lower than 3 MW/m2. The effective ion charge number, Zeff, at the core boundary is below three, which can be further reduced by increasing the upstream D2 puffing rate. A higher D2 puffing rate helps to increase electron density (ne) in scrape-off layer (SOL) and the impurity screening ability. Based on the SOLPS modeling results, the lifetime of tungsten (W) divertor targets has been estimated by using the DIVIMP code, which indicates that W sputtering is mainly contributed by Ne ions at a far SOL region due to high electron and ion temperature (Te and Ti) there. Upstream D2 puffing can reduce the W erosion rate and W impurity concentration inside the separatrix due to decreasing Te and Ti at the far SOL region. The modeling results show a viable operation regime for the CFETR divertor.

The phenomenon of multifaceted asymmetric radiation from the edge (MARFE) is investigated with impurity gas puff from the upper divertor on the Experimental Advanced Superconducting Tokamak (EAST). A typical process in which dense radiation region in the vicinity of the X point (X-point MARFE) further evolves into MARFE on the high field side (wall MARFE) after the plasma ma kes a transition from H-mode to L-mode confinement is observed in discharges with the impurity gas seeding. The electron density distribution and evolution in the divertor volume are measured by means of spectroscopy. It is observed in the experiments that the final position of MARFE is related to the ion ∇B drift direction. After the phase difference of n = 1 resonant magnetic perturbation (RMP) change from 90 • to 270 • , MARFE begins to appear on the high field side, which may be caused by the density pump-out induced by RMP. At the same heating power, the density threshold for MARFE formation is somewhat higher in the Ne seeding discharge than in the Ar seeding discharge. This may be attributed to the fact that the divertor radiation fraction, P rad,div /P rad,main , in the Ne seeding discharge is lower than that in the Ar seeding discharge. In addition, MARFE is successfully suppressed by total radiated energy feedback control in radiative divertor experiments. Therefore, radiation feedback control may play a vital role in avoiding major disruption induced by impurity radiation in radiative divertor experiments.

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