7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

SOLPS-ITER modeling of edge plasma and impurity transport in EASTFuqiong Wang1,2, Y.F. Xu1,2, Y. Liang3, X.J. Zha1,2, F.C. Zhong1,2, S.T. Mao4, Y.M. Duan4, L.Q. Hu4
1
Department of Applied Physics, College of Science, Donghua University, 2 Member of Magnetic
Confinement Fusion Research Center, Ministry of Education, China, 3 Forschungszentrum JülichGmbH, Institut für Energie- und Klimaforschung Plasmaphysik, 4 Institute of Plasma Physics,Chinese Academy of Sciencese-mail (speaker): wangfq@dhu.edu.cn
The comprehensive SOLPS-ITER [1, 2] code package
has been utilized to analysis drift effects on scrape-offlayer (SOL) widths [3], e.g. the power decay length 𝜆𝑞,
and on the divertor detachment and asymmetry in EAST
plasmas with favorable and unfavorable toroidal
magnetic field (BT) direction, i.e. with the ion B×B
drift pointing towards and away from the active X-point.
To gradually highlight the role of the drift-based
neoclassical mechanisms in the radial particle transport,
the turbulent transport level (i.e. DSOL) has been scanned
from high (1.0 m2/s) to extremely low (0.02 m2/s). It isfound that the drift-driven transport, considered as thekey process in the formation of SOL plasma profiles, ismagnetic-field-direction dependent and thus SOL flows
and currents as well as the SOL widths can be obviously
affected by the direction of drifts. With BT changed fromthe favorable direction to the unfavorable one, theflattening of density radial profile as well as the increaseof power decay length, in the SOL, can be achieved andcan be further enhanced as the weight of turbulent
transport (i.e. DSOL) gets reduced, due to the increased
contribution of ion parallel viscosity to the radial ionflow. Particularly, with DSOL ≤ 0.05 m2/s in thesimulations, the dominant role of drift-based neoclassicalmechanisms in the radial particle transport will lead tothe formation of the so-called edge density-shelf [4] inplasmas with unfavorable BT. Power scrape-off width inplasmas with unfavorable-BT is much insensitive to theturbulent transport level and can remain to be relativelyhigh even when DSOL has been decreased to be extremely
low. Due to the compressing/widening effect of thedrift-driven inward/outward radial particle flow, thesimulated power scrape-off width exhibits an in-out
asymmetry, which is also magnetic-field-direction
dependent.
Besides, drift effects on divertor detachment,
asymmetry and impurity transport in the neon (Ne)seeded EAST plasmas with both BT directions have also
been investigated. Firstly, electrostatic potential/field
distribution has been analyzed, which reveals that infavorable BT divertor electric potential profile follows
the classical picture; while in unfavorable BT theso-called X-point potential well forms in detachedplasmas, when Pfirsch-Schl𝑢̈ ter currents dominate theparallel current, compressing/widening radial density
profile in the inner/outer divertor. In the confinement
region, it is found that magnitude of the radial electricfield (Er) is close to its neoclassical value, and that Er forunfavorable BT is smaller than that for favorable BT due
to the smaller neoclassical contribution related to radial
density gradient. In accordance with the experimentalobservations in EAST, simulation results demonstratethat in favorable BT the onset of detachment is highly
asymmetric between the inner and outer divertors; andthe magnitude of in-out asymmetry in divertor
detachment can be largely decreased by reversing BT,
physics reasons for which have been explored. It is foundthat, apart from the well-known EB drift particle flowfrom one divertor to the other through the private flux
region (PFR), heat flow through the SOL, particularly
power flow from the upstream to divertor, is also a
critical parameter affecting divertor detachment andasymmetry. In-out asymmetry in neon-seeding inducedpressure loss along flux surface in the SOL tends to drivea convective heat flow from the hotter to the colder side,making upstream power flow into the colder divertor
region more insensitive to neon seeding level. Besides,
position of the stagnation-point for poloidal neon ion
velocity profile, a key element determining neon
leakage/retention in divertor, can be greatly affected byP-S flow direction, EB drift and by divertor operation
regimes depending on neon seeding level. Hence,leakage of neon from divertor is found to be muchsensitive to neon seeding level and BT direction. The
former can also affect the neon ionization source
distribution, as another key factor determining neon
divertor retention/leakage.
References[1] S Wiesen et al 2015 J. Nucl. Mater. 463 480–484[2] X Bonnin et al 2016 Plasma Fusion Res. 11 1403102[3] Fuqiong Wang et al 2022 Nucl. Fusion 62 056021[4] Wang H.Q. 2020 Phys. Rev. Lett. 124 195002