Direct optimization of neoclassical ion transport in stellarator reactors

Abstract

We directly optimize stellarator neoclassical ion transport while holding neoclassical electron transport at a moderate level, creating a scenario favorable for impurity expulsion and retaining good ion confinement. Traditional neoclassical stellarator optimization has focused on minimizing ${\epsilon }_{\mathrm{eff}}$, the geometric factor that characterizes the amount of radial transport due to particles in the $1/\nu$ regime. Under expected reactor-relevant conditions, core electrons will be in the $1/\nu$ regime and core fuel ions will be in the $\sqrt{\nu }$ regime. Traditional optimizations thus minimize electron transport and rely on the radial electric field $\left(E_r\right)$ that develops to confine the ions. This often results in an inward-pointing $E_r$ that drives high-$Z$ impurities into the core, which may be troublesome in future reactors. In this work, we increase the ratio of the thermal transport coefficients $L_{11}^e/L_{11}^i$, which previous research has shown can create an outward-pointing $E_r$. This effect is very beneficial for impurity expulsion. We obtain self-consistent density, temperature, and $E_r$ profiles at reactor-relevant conditions for an optimized equilibrium. This equilibrium is expected to enjoy significantly improved impurity transport properties.

Reviewers requested focusing on a single optimized configuration rather than three

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Cited by in corpus (1)

• Electron root optimisation for stellarator reactor designs