Flux Divergence Evaluation in Partially Ionized Plasmas Using a Continuity Equation in the Presence of Magnetic X-Point Configurations

The dynamics of partially ionized plasmas in the presence of magnetic X-point configurations are crucial for understanding various plasmas such as fusion and astrophysical plasmas. A cylindrical Langmuir probe array is utilized in the MAgnetic X-poInt siMUlator System (MAXIMUS) [1] to explore the transport behaviours of such plasma configurations. In this setup, low temperature plasmas are generated within the separatrix using argon gas and DC-heated filaments as plasma sources. From the obtained electron energy distribution functions (EEDFs) and relevant atomic data such as electron-impact ionization cross sections, collisional source terms and sink terms in local continuity equation can be evaluated quantitatively. Under the steady state assumption, the divergence of the charged particle flux (flux divergence) can be determined indirectly from the local continuity equation. The effects of varying plasma control parameters and boundary conditions, such as the bias voltage of DC filaments and the neutral pressure on the spatial profiles of flux divergence are discussed. Additionally, the diffusion coefficients at the magnetic X-point inferred from flux divergence are discussed under identical conditions.