Macroscopic trends of neoclassical tearing stability in high-field H-mode tokamak pilot plants

Abstract The neoclassical tearing mode (NTM) stability metric—minimum marginally stable island width w m ∗ —was compared across 14651 inductive high-field tokamak pilot plant equilibria. Larger devices with reduced elongation and/or increased minor radius demonstrated an order-of-magnitude increase in w m ∗ , primarily due to a reduction in bootstrap drive. This work is part of an ongoing effort to ensure passive NTM-stability in the ARC tokamak, in which the technology to achieve active tearing-suppression with localised electron cyclotron current drive does not yet exist. The equilibrium scenarios in the database were Monte Carlo generated and normalised to the same > 400MW fusion power, minimum pressure scenario at a range of plasma currents, before tearing analysis using the modified Rutherford equation was applied for all resonant poloidal and toroidal m , n modes up to n = 4. Single-helicity toroidal Δ ′ calculations in resistive DCON set the minimum marginally stable island width, and a simple modal scaling proportional to − m 2 n − 1 was identified for high- m Δ ′ values. The dominant correlates of w m ∗ and Δ ′ across the database were analysed using interpretable machine learning techniques.