SOLPS-ITER drift modeling of neon impurity seeded plasmas in EAST with favorable and unfavorable toroidal magnetic field direction

Abstract

To better understand divertor detachment and asymmetry in the Experimental Advanced Superconducting Tokamak (EAST), drift modeling via the comprehensive edge plasma code SOLPS-ITER of neon impurity seeded plasmas in favorable/unfavorable toroidal magnetic field (B T) has been performed. Firstly, electrostatic potential/field (/E) distribution has been analyzed, to make sure that and E are correctly described and to better understand drift-driven processes. After that, drift effects on divertor detachment and asymmetry have been focused on. In accordance with the corresponding experimental observations, simulation results demonstrate that in favorable B T the onset of detachment is highly asymmetric between the inner and outer divertors; and reversing B T can significantly decrease the magnitude of in-out asymmetry in the onset of detachment, physics reasons for which have been explored. It is found that, apart from the well-known E × B drift particle flow from one divertor to the other through the private flux region, scrape-off layer (SOL) heat flow, which is much more asymmetrically distributed between the high field side and low field side for favorable B T than that for unfavorable B T, is also a critical parameter affecting divertor detachment and asymmetry. During detachment, upstream pressure (P u) reduction occurs and tends to be more dramatical in the colder side than that in the hotter side. The convective SOL heat flow, emerging due to in-out asymmetry in P u reduction, is found to be critical for understanding divertor detachment and asymmetry observed in EAST. To better understand the calculated drastic power radiation in the core and upstream SOL, drift effects on divertor leakage/retention of neon in EAST with both B T directions have been addressed for the first time, by analyzing profile of poloidal neon velocity and that of neon ionization source from atoms. This work can be a reference for future numeric simulations performed more closely related to experimental regimes.