Modelling study of divertor W leakage for different divertor conditions with Ne seeding in EAST tokamak

Sequential SOLPS-ITER and DIVIMP simulations are carried out for tungsten (W) edge transport during neon (Ne) injection in EAST, elucidating the pathway of W impurity leakage from the divertor to the core plasma under different dissipative divertor conditions. Divertor conditions from low-recycling to detachment are generated by modulating the Ne injection rate in the SOLPS simulation. With the drift velocities incorporated in DIVIMP, W transport under the drift effect is investigated. For low-density L-mode plasma conditions with favorable Bt direction, the majority of W source originates from the outer divertor target and leaks upstream through the near-SOL E× B drift reversed region at both inner and outer divertors. The E× B drift is demonstrated to have a significant effect on W leakage and the effect diminishes with the increase of Ne injection rate. Compared to the D2 injection cases, Ne injection helps to achieve a strong dissipative divertor condition at a much lower plasma density, resulting in a higher W leakage ability due to the smaller friction with the background plasma. For Ne injection cases under high-density H-mode conditions, W leaks mostly through the outer divertor region while the inner divertor is fully detached. Compared to the L-mode cases, the shorter power decay lengths in the scrap-off layer (SOL) of the H-mode cases result in smaller parallel E× B drift velocities especially in the middle and far SOL region. With the increase of the Ne injection rate, the decrease of the E× B drift in the middle SOL leads to a wider near-separatrix W leakage path. Therefore, a worse divertor W screening is expected, which is consistent with the previous published experimental observations (Ding et al 2022 Nucl. Mater. Energy33 101250).