Simulation Study of local closure effect of the Divertor structure on Detachment Density in CFETR

Full text: The need for advanced divertor solutions to efficiently dissipate heat from fusion reactors is critical because the maximum steady-state power load is limited to q_t ≤5– 10 MWm −² to a plasma facing component (PFC) target surface, whether solid or liquid, while the undissipated power loads will be an order of magnitude higher. Previous work shows that the tightly closed divertor greatly improves trapping of recycling neutrals, thereby increasing radiative and charge exchange losses in the divertor and reducing the electron temperature Tet and deposited power density q_dep at the target plate. We studied the local closure effect of the divertor structure on the detachment density in CFETR by using the scrape-off layer plasma simulation (SOLPS) code. The divertor geometry near the striking point was set as a semicircle structure. The local closure of striking point was changed by reducing the radius of the semicircle step by step with all the other parameters fixed the same. The simulation results reveal that the heat flux show great differences in low density case and high density case. In low density case, the applied of semicircle structure (r~10cm) can hardly change the heat flux of the striking point. Yet, for the high density case, the semicircle structure will greatly reduce the temperature of the striking point, thus enhance the density of the neutral gas. In other words, the increased local closure effect will significantly reduce the heat flux of the striking point and help reduce the threshold density of the detachment. (author)