Negative-triangularity turbulence suppression in a compact spherical tokamak: nonlinear CGYRO gyrokinetics across ion and electron scales (KRONOS config-22021)

Nonlinear CGYRO gyrokinetic simulations confirming that negative triangularity (δ = −0.30) suppresses core turbulent transport in the KRONOS config-22021 spherical-tokamak breeder. Four independent, mutually-consistent calculations: Ion scale (BR-L2-A1c): ~40% suppression (converged NT/PT pair ~38–42%), converged and saturated at real electron mass μ=3672, ITG+TEM, operating gradient a/L_T=3.0, kinetic electrons. Electron scale (REG-P13): ~80% suppression (ETG, Q_e 23.4 vs 110.7 @ a/L_Te=3.0), μ=400 — standard ETG practice, stated as a method condition. Collisionality robustness (BR-L2-A13): suppression holds 56–66% across ν* ×0.25–4. Full spectrum (BR-L2-A18c): NT γ 31–60% below PT at every resolved k_y (0.1–6.0); k_y=10 flagged unconverged and excluded. Code: CGYRO (General Atomics), GPU gyrokinetic solver. TCV/DIII-D negative-triangularity databases corroborate the direction and magnitude. Physics and engineering only; economics are excluded.