Modeling on the divertor power deposition in EAST discharges with magnetic perturbations induced by lower hybrid waves via the field-line diffusion model

Abstract A Monte-Carlo field-line diffusion (FD) model has been realized and utilized to analyze the divertor heat flux pattern in EAST discharges with magnetic perturbations induced by lower hybrid waves (LHWs). This work mainly concerns the influence of LHW-induced magnetic perturbation on the position and shape of divertor power deposition, as well as that on the wetted area, Awet defined as the ratio of the integral power deposition P t a r g to the peak heat flux q p e a k on the target surface (i.e. A w e t = P t a r g / q p e a k ). Firstly, the cross-field transport coefficient has been scanned from 0.2 to 3.0 m2/s in the FD model simulations, results of which suggest that, with the enhancement of perpendicular diffusion, divertor power deposition extends from the surface regions connected by longer field lines towards the regions connected by shorter ones, and thus the wetted area has been evidently increased. Secondly, effects of magnetic perturbation amplitude on divertor power deposition have been explored by gradual increasing the total current of helical filaments in the FD model simulations. Results reveal that, with the enhancement of LHW-induced perturbation, the poloidal projection of the perpendicular transport will be affected due to the increased field-line stochasticity, and that, simultaneously, the parallel transport will be influenced due to more and more direct parallel connections of the divertor surface to the plasma core established by the perturbed field lines. Consequently, with an increasing of the LHW-induced magnetic perturbation, the wetted area first increases then decreases, and the ratio of heat flux between the striated and original strike lines increases gradually, which has also been observed in the EAST experiment campaign as the LHW power increases. These results can facilitate the estimation and control of the peak divertor heat flux, which is of vital importance to the long-pulse high-performance operation of EAST, in LHW-perturbed discharges. Moreover, before the FD model analysis of divertor heat flux pattern in EAST discharges with LHW-induced magnetic perturbations, the reliability of this model has been assessed by comparing results from the FD model against those from the elaborated EMC3-EIRENE code and experimental measurements using Infra-red (IR) camera.