We present new and updated methods for reducing transport caused by electrostatic ion-temperature-gradient (ITG) driven turbulence in quasi-isodynamic (QI) configurations. We first show an updated model for the threshold (critical) gradient of localised toroidal ITG modes. It is then argued that it is desirable for ITG modes to ‘split’ and localise in separate curvature drift wells, which is leveraged to produce a six-field-period QI configuration with a high critical gradient. We show that the destabilising effect of kinetic electrons (Costello & Plunk 2025 J. Plasma Phys. vol. 91, p. E12) on localised ITG modes can be minimised in a magnetic field structure, which we dub ‘inverse mirror’. Applying a general optimisation target that improves ITG stability above the critical gradient yields an inverse mirror configuration which maintains heat fluxes below or equal to the W7-X high mirror configuration for a range of applied density gradients.
Roberg‐Clark et al. (Sun,) studied this question.