Negative-Triangularity Turbulence Suppression in a Compact Spherical-Tokamak Breeder: Nonlinear Gyrokinetics of the Quiet Operating Point

Nonlinear gyrokinetics of the compact spherical-tokamak breeder at the frozen negative-triangularity design point. Nonlinear CGYRO with kinetic electrons shows negative triangularity cutting ion-scale (ITG+TEM) transport by 40-45 percent versus a positive-triangularity twin, with the operating point quiet and subcritical; electron-scale runs show 79-80 percent ETG suppression. Direction corroborated against TCV and DIII-D. Reduced electron mass and design-target caveats stated openly.