Influence of Hall effect and toroidal flow on the plasmoid formation and incomplete reconnection in a low resistivity plasma in tokamak

The nonlinear resistive-kink mode in the low resistivity plasma in tokamak is investigated through the three-dimensional, toroidal, and nonlinear Hall-MHD code CLT. It is found that, without the two-fluid effect and the toroidal flow, the system can evolve into a steady-state with the saturated main m/n = 1/1 magnetic island and the co-existing large secondary island. The main m/n = 1/1 magnetic island cannot push the hot core plasma out of the q = 1 surface as it does in Kadomstev's model, and the reconnection is incomplete. However, with the two-fluid effect or the toroidal flow, the nonlinear behaviors of the resistive-kink mode could be essentially different. The two-fluid effect and the toroidal flow can break the symmetry during the plasmoid formation, which destroys the balance between the main m/n = 1/1 magnetic island and the large secondary island. The large secondary island is then merged into the main m/n = 1/1 island. After that, the main m/n = 1/1 island finally occupies the whole mix region, and all magnetic flux in the mix region is reconnected. A similar simulation study has been done in periodic cylindrical geometry (Gunter et al 2015 Plasma Phys. Control. Fusion 57 014017), while our work is done in tokamak toroidal geometry. The toroidal effect has also been investigated, and we find that the widths of the main 1/1 island and the secondary island slightly increase with increasing aspect ratios.

Automated summary

In this study, the nonlinear resistive-kink mode in low resistivity plasma in tokamak was investigated using a 3D, toroidal, nonlinear Hall-MHD code. It was discovered that the effect of two-fluid dynamics and toroidal flow can significantly alter the behavior of the resistive-kink mode, leading to a different evolution of magnetic islands and reconnection processes. Additionally, the investigation into the toroidal effect showed that the widths of the main m/n = 1/1 island and the secondary island slightly increase with increasing aspect ratios.