A 2D two-fluid MHD code to model partially ionised plasma: calibration and benchmarking

In the lower solar atmosphere, there exists partially-ionised plasma and such an environment significantly changes the dynamics of the plasma-to-magnetic-field interaction. Appropriate numerical treatment of this requires a more complex description than single-fluid magnetohydrodynamics (MHD) can provide. A 2D two-fluid MHD code is developed to simulate partially-ionised plasma. The code is validated through various standard tests to demonstrate a high level of accuracy and stability. These tests include the Sod-shock tube test in hydrodynamics and the Brio-Wu shock and Orszag-Tang vortex test in MHD. The two-fluid simulation is calibrated against a 1D slow-mode MHD shock, known as the switch-off shock. Additionally, ionisation and recombination rates were included and their effect on the properties of the switch-off shock is investigated. Furthermore, we initiate the Orszag-Tang vortex in the two-fluid setting and present the results as a future 2D two-fluid benchmark.