Coarse-grained gyrokinetics for the critical ion temperature gradient in stellarators

Coarse-grained gyrokinetics for the critical ion temperature gradient in stellarators

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We present a modified gyrokinetic theory to predict the critical gradient that determines the linear onset of the ion temperature gradient (ITG) mode in stellarator plasmas.A coarse-graining technique is applied to the drift curvature, entering the standard gyrokinetic equations, around local minima.Thanks to its simplicity, this novel formalism yields an estimate for the critical gradient with a computational cost skull bride and groom low enough for application to stellarator optimization.When comparing against a gyrokinetic solver, our results show good agreement for an assortment of stellarator designs.

Insight gained here into the physics of the onset of the ITG-driven instability enables us to devise a compact configuration, similar to the Wendelstein 7-X device, but with almost twice the ITG linear click here critical gradient, an improved nonlinear critical gradient, and reduced ITG mode transport above the nonlinear critical gradient.