Effects of strike point location on the divertor particle and energy flux decay widths on EAST by experiment and SOLPS modeling

Abstract

The new lower tungsten divertor of EAST uses a right-angle shape consisted by horizontal and vertical targets, which has the capacity of increasing the divertor closure. The strike point (SP) sweeping experiment is carried out to (1) avoid long-term deposition of particle and heat flux at the same location, thus protecting the target, (2) study the dependence of power control capability on the SP location. The particle and energy flux densities to the target depends strongly on their decay width. Therefore, it is important to know how the SP location influences the outer target (OT) particle parallel λjs,OT and OT parallel heat flux decay widthsλq,OT. In this work, SOLPS-ITER simulations combined with SP sweeping experiment are applied to study this issue. Four cases, which are taken from different time during SP sweeping (including both horizontal and vertical divertor) in L-mode experiment with high heating power, are selected for investigation. The simulation result is in satisfactory agreement with experiment data, suggesting the simulation is valid. The results indicate that the SP location can affect neutral particles accumulation and ionization positions, thus affecting λjs,OT and λq,OT. (1) When SP is located in horizontal target, the higher neutral particle ionization in common flux region (CFR) leads to wider λjs,OT than those of vertical target. (2) When SP is located on horizontal target, the divertor power radiation is higher than that of vertical target, resulting in wider λq,OT. (3) Increasing upstream plasma density can effectively broaden λq,OT, while λjs,OT remains almost unchanged. This study improves the understanding of the influence of divertor shape on λjs,OT and λq,OT, and can be applied to heat flux control during long-pulse high-power discharges on EAST.