Ion Landau Damping on Drift Tearing Modes

Kinetic treatments of drift-tearing modes that match an inner resonant layer solution to an external MHD region solution, characterised by $\Delta^{\prime}$, fail to properly match the ideal MHD boundary condition on the parallel electric field, $E_{\parallel}.$ In this paper we demonstrate how consideration of ion sound and ion Landau damping effects achieves this and place the theory on a firm footing. As a consequence, these effects contribute quite significantly to the critical value of $\Delta^{\prime}$ for instability of drift-tearing modes and play a key role in determining the minimum value for this threshold.