Tearing Stability Prediction Combining Toroidal Calculations With a Two-Fluid Slab Layer Approximation*

We have begun development of a new tearing mode (TM) stability calculation that combines the toroidal outer region Δ' with two-fluid and drift MHD effects in the inner layer Δ'. Current TM analysis methods are susceptible to numerical instabilities and uncertainties in the equilibrium input quantities, leading to unreliable estimates of the tearing stability index Δ'. To address these challenges, we match outer region Δ' calculations that include toroidal and poloidal shaping effects from STRIDE to inner layer slab-approximated, two-fluid Δ' calculations from SLAYER. Critically, finding such inner-outer layer matches yields a mode growth rate γ for each rational surface in the shaped plasma, which provides greater insight toward the TM stability of the equilibrium than Δ' calculations alone. We demonstrate these rational surface TM growth rate analyses on a variety of both analytical and reconstructed tokamak equilibria, showing their numerical robustness. Improving the capability to predict classical tearing onset in tokamaks could facilitate discovery of TM stable operational regimes and avoid disruptions in future devices. This workflow is being incorporated into the Generalized Perturbed Equilibrium Code (GPEC) package.