Assessing the Impact of Plasma Density, Sputtering, and E × B Drift on Divertor Plates Detachment in a Small-Size Tokamak

Abstract

The edge transport barrier (ETB) on small-size divertor tokamak (SSDT) causes a detached regime. The B2SOLPS5.02D multifluid code simulates the drifts on edge plasma in the detached divertor regime. In SSDT, two case studies: (i) the core plasma density had been adjusted (4, 6, 8 × 10¹⁹ and 1 × 10²⁰ m⁻³) with a set sputtering coefficient of 1.1%, and (ii) the sputtering yield was changed (0.4%, 0.6%, 0.8%, 1% and 1.2%) with a constant core plasma density of 4 × 10¹⁹ m⁻³ have been conducted. The 2D simulations show that, during transitioning to detached conditions in SSDT with ETB formation mode with forward field configurations, the low field side (LFS) divertor target heat flux is directly impacted by the cross-field drifts and flows. The simulation demonstrated that, concerning the electron temperature, the two divertor plates are detached at higher density while at lower density, the HFS plate is considered as ‘attached plate’. Additionally, as the core plasma density increases, the peaks of poloidal electron heat flux of the HFS plate were increased insignificantly, while it is strongly increased in the LFS plate. Moreover, as the core density is raised into the detached domain, some characteristics of the detachment processes, such as a roll-over in the ion-saturation current and a cliff in the electron temperature nearby the divertor plates, have been observed. Involving of the carbon sputtering in the detachment cliff formation is also established. Finally, a correlation is found between the development of a detached cliff and the rise in the SOL width.