Influence of the drifts on the double‐peaked emission profile of the visible light in the upper divertor region of EAST.

A novel double‐peaked emission profile has been observed by the visible light imaging system in EAST. In the upper divertor region, two emission peaks in the high‐field side (HFS) scrape‐off layer (SOL) and near the X‐point are identified by tomographic reconstruction. In our previous SOLPS‐ITER simulation work, the emission peaks in the HFS SOL and near the X‐point are attributed to the carbon deposition on the HFS baffle and the dome of the upper tungsten divertor, respectively. The appearance of the emission peak near the X‐point when the outer target is attached was understood by analysing the carbon transport in the private flux region (PFR). However, the simulated intensity of the emission peak in the HFS SOL is lower by one order of magnitude than that in the PFR, while they are at the similar level in the experiment. In this work, the influence of the drifts is further studied by SOLPS‐ITER simulations. Under the favourable toroidal field condition, the HFS SOL plasma transits to the detachment regime. The chemical sputtering of the carbon deposited on the inner baffle increases significantly, as well as the emission intensity of the peak in the HFS SOL. Meanwhile, the C2+ density peak in the PFR decreases due to the E × B drift towards inner target. The emission intensity in the PFR near the X‐point, therefore, decreases moderately. As a result, the intensities of the two emission peaks become comparable, which matches better with the experiment. [ABSTRACT FROM AUTHOR]