Tungsten core accumulation study in EAST plasma with lower tungsten divertor by kinetic impurity transport model

Tungsten (W) impurity transport and the corresponding core W accumulation is a critical issue in tokamak with W as plasma facing material. In this work, a kinetic W impurity transport code based on the guiding center approximation is applied for the study. The background plasma and simulation mesh are provided by 2D fluid code SOLPS. The new code can simulate the creation and transport of W impurity in the boundary region of a tokamak. The W impurity moves in two directions: the parallel transport is determined by the forces such as friction force and ion temperature gradient force, and the radial transport is dominated by the anomalous transport. The code is benchmarked against the impurity transport code DIVIMP using the lower single null configuration of EAST, and the similar radial and poloidal distributions of W density are obtained in both codes. The correlation between the W density at core edge (nW,core), the parallel forces on impurity, and anomalous diffusion is studied. It is found that the competition between friction force and ion temperature gradient force significantly affects the penetration of W impurity to the core region. The enhancement of anomalous diffusion coefficient (DAN) reduces the penetration rate, which further decreases the nW,core. The average dwell time of W particles in the core (sW,core) also influences nW,core, i.e. longer sW,core leads to higher nW,core. Moreover, larger DAN can reduce sW,core by enhancing the impurity exhaust from core, thus further suppress W core accumulation.

Automated summary

In this study, a kinetic W impurity transport code based on the guiding center approximation is used to investigate the creation and transport of W impurity in the boundary region of a tokamak. The results show that the competition between friction force and ion temperature gradient force significantly affects the penetration of W impurity to the core region, while an increase in the anomalous diffusion coefficient decreases the penetration rate. Moreover, the average dwell time of W particles in the core also influences the W density at the core edge.