Plasma-surface interactions in magnetized electronegative plasmas: effects of electron Kappa distribution function on presheath dynamics

Abstract The effect of superthermal electrons on presheath dynamics in magnetized electronegative plasmas remains insufficiently characterized, limiting the predictive capability of plasma–surface interaction models. In this study, we examine the presheath behavior of a thermal, magnetized electronegative plasma in which electrons follow a Kappa distribution, thereby extending beyond the conventional Maxwellian assumptions to incorporate non–equilibrium electron properties. A fluid model is employed, coupling the continuity and momentum equations for thermal positive ions with Poisson’s equation, solved self–consistently under ionizing collisional conditions. We investigate the influence of the spectral index of electron Kappa distribution, magnetic field strength, electronegativity, and positive ion temperature on key presheath characteristics. The results show that magnetic fields and negative ions significantly compress the presheath region. Decreasing the spectral index intensifies the presheath electric field, shifting the space–charge peak toward the plasma–presheath boundary and reducing its amplitude. Magnetic fields and superthermal electrons lead to suppression of the positive ion flux to the wall. Ion trajectory analysis reveals that higher positive ion temperatures and lower spectral indices reduce magnetic deflection, enabling ions to realign with the presheath axis over shorter distances. The floating potential exhibits strong sensitivity to both the spectral index and electronegativity, while magnetic effects diminish at high positive ion temperatures. Furthermore, the negative ion concentration exerts an increasingly pronounced influence on the floating potential at low spectral indices and when electrons significantly deviate from equilibrium. Taken together, these results establish the spectral index of the Kappa distribution as a key controlling parameter that governs presheath structure, positive ion acceleration, and wall–interaction characteristics in thermal magnetized electronegative plasmas.