Effect of divertor plasma-facing materials and drift on the power decay width in the scrape-off layer and divertor on EAST

The narrow power decay width lambda(q) may lead to high heat flux density to the divertor target, which is one of the most severe challenges for future fusion devices. EAST has upgraded its lower graphite (C) divertor to a tungsten (W) one, and it is important to reveal the dependence of lambda(q) on the divertor condition. In the present work, SOLPS-ITER is applied to estimate the effect of various conditions [C/W plasma facing material (PFM), with/without drift] on lambda(q) of EAST in attached divertor regime. The simulation results confirm that the power decay width of the upstream lambda(q,SOL), divertor lambda(q,)(OT), and private-flux region (PFR) S-OT all depend on the PFMs and drifts. However, the effect of PFM on lambda(q,SOL), is slight, while it has a significant influence on lambda(q,)(OT) and S-OT. In the upstream, positive correlation between lambda(q,SOL), and v(SOL)* is obtained, and the simulation is in qualitative agreement with the two-point model. Both lambda(q,SOL) and lambda(q,OT) in without drift case are larger than that of with drift case. The regression of simulation results is obtained, showing a strong positive correlation between SOL collisionality v(SOL)* power radiation friction in divertor region f(rad,)(OD) and lambda(q,)(OT). Thus, the C PFM with intrinsic impurity has the largest lambda(q,)(OT). In the PFR, S-OT with drift is smaller than that of without drift. Moreover, the combination of more D atoms accumulation and stronger E-p x B drift lead to larger S-OT in W PFM case than that of C PFM case.

Automated summary

Investigated the influence of divertor conditions on the power decay width (λ(q)) in EAST fusion device. Simulation results show that the power decay width and cooling effect in the divertor region are significantly affected by PFM (plasma facing material) and drift.