Simulation of tungsten impurity transport by DIVIMP under different divertor magnetic configurations on HL-3

Abstract

Tungsten (W) accumulation in the core, depending on W generation and transport in the edge region, is a severe issue in fusion reactor. The divertor plasma parameters, such as heat flux to the target, can be effectively suppressed by changing the divertor magnetic configuration. Nevertheless, its impact on W core accumulation remains unclear. The HL-3 tokamak has advantage of operating with flexible divertor configurations, e.g. standard divertor (SD) and snowflake divertors (SFD). In this study, DIVIMP combined with SOLPS-ITER is applied to investigate the effects of divertor magnetic configurations (SD vs SFD) on W accumulation during neon injection in HL-3. It is found that W concentration in the core of SFD is significantly higher than that of SD with similar total W erosion flux. The reasons are: (1) W impurities in the core of SFD mainly originate from inner divertor, which has short leg, and the source is close to the divertor entrance and upstream separatrix. Furthermore, the SW0 is much stronger, especially near divertor entrance. (2) the region overlap of SW0 and F_(W,TOT) pointing to upstream promote W accumulation in the core. Moreover, influence of W source locations at inner target on W transport in the SFD is investigated. Tungsten impurity in the core is mainly contributed by target erosion at common flux region (CFR) away from strike point. This is attributed to that W source at this location enhances ionization source above the W ion stagnation point, which sequentially increases W penetration. Therefore, the suppression of far SOL inner target erosion can effectively prevent W impurities from accumulating in the core.