Work

Impact of E × B drift on tungsten impurity transport and analysis of its instantaneous response: a particle Monte Carlo simulation

Year: 2025

Type: article

Abstract: Tungsten (W), as the primary plasma-facing material in tokamaks, is incompatible with the core plasma. Even extremely low concentrations of W impurities can contaminate the plasma. Therefore, the transport and core accumulation of W impurities are among the key challenges in the fusion community. In this study, the impurity transport code IMPEDGE is upgraded to include the effect of E × B drift, and then applied to investigate the impact of E × B drift on W impurity transport in single-null configuration on EAST. It is found that E × B drift not only affects the stagnation point location of W impurities but also exhibits an instantaneous response feature—i.e. it governs the impurity motion on a time scale shorter than the collisional relaxation and exceeding the gyro-period. The instantaneous response of E × B drift governs impurity behavior near the divertor targets and significantly affects the core W impurity density ( n ¯ W , c o r e ). By comparing different E × B drift directions, it is found that the region of reversed E × B drift widens with increasing of neon (Ne) injection rate under forward B t , leading to an increase in n ¯ W , c o r e . The instantaneous response of E × B drift can induce a deposition phenomenon distinct from prompt redeposition. To evaluate this behavior, this work establishes a simplified theory for analysis. The poloidal drift deposition distance ( x c , p o l ) is defined. When x c , p o l exceeds the W ionization mean free path ( λ W mfp ), impurities tend to return to the target due to the effect of E × B drift’s instantaneous response. This deposition behavior is more likely to occur under conditions of high electron temperature ( T e ) and high drift velocity ( v E r × B ). Simulation results demonstrate that this theory can effectively identify W deposition induced by the instantaneous response of E × B drift. An equivalent force model was introduced in the simulation and compared with the instantaneous effect of E

Source: Nuclear Fusion

DOI: 10.1088/1741-4326/ae1c4f