Turbulence mitigation in maximum-J stellarators with electron-density gradient

In fusion devices, the geometry of confining magnetic field has a significant impact on instabilities that drive turbulent heat loss. This is especially true stellarators, where density-gradient-driven branch ‘trapped electron mode’ (TEM) predicted to be linearly stable if maximum-J property, as very approximately case in certain configurations Wendelstein 7-X experiment (W7-X). Here we show, using both analytical theory and simulations, benefits optimisation W7-X also serve mitigate ion-temperature-gradient (ITG) modes long an density gradient present. We find effect indeed carries over nonlinear numerical low TEM-driven transport, reduced ITG turbulence presence gradient, giving theoretical support for existence enhanced confinement regimes, strong gradients (e.g. hydrogen pellet or neutral beam injection).