The transport of tungsten impurities induced by the intrinsic carbon during upper-single null discharge on EAST tokamak

Abstract

• SOLPS-DIVIMP modeling is applied to the production and transport of W impurities on EAST. • High n e , s e p OMP suppresses W impurity, while higher input power enhances W concentration. • Strong correlation between T e at the outer target and W ion density at core is observed. • T e < 20 eV is required to maintain W concentration at CEI < 10 −5 in steady-state scenarios. The transport as well as accumulation of tungsten (W) impurity is one of the critical issues for the W divertor operation. The EAST tokamak with W and graphite divertor targets, provides a good platform for the investigation of W impurity behaviors. In this work, the production, transport and accumulation of W impurities are simulated via the SOLPS-DIVIMP modeling. The plasma background is obtained by the SOLPS simulations, while the W sputtering yield is calculated via empirical formula, and the following W transport is traced using the DIVIMP code. The W impurity source is mainly contributed by the incidence of carbon (C) impurity in this simulation. The distribution of W ions with different charge states is obtained and the transport of the W ions is analyzed by the net forces. The dependences of W impurity on the n e , s e p OMP and P SOL are illustrated, which show the divertor plasma has great impact on the W impurity distribution. The increase of n e , s e p OMP can suppress the W impurity in the core region with the fixed P SOL , while higher input power can enhance the W concentration significantly. The W impurity can lead to sufficient power radiation due to strong impurity source and high radiation rate in the core region during low density discharge, while the influence becomes weaker as n e , s e p OMP raises. The effects of self-sputtering on the W impurity accumulation are also discussed. With the increment of P SOL , the sputtering and self-sputtering of W increase remarkably, leading to the W ions concentration exceed 10 −5 in the core–edge interface (CEI). Moreover, the strong correlation between T e at the outer target and W ion density at CEI is observed, showing that T e < 20 eV is required to maintain W concentration at CEI below the acceptable limitation (10 −5 ) in steady-state scenarios in EAST (without ELMs).