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 $L_{1 1}^{e}/L_{1 1}^{i}$, 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.
- Publication:
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arXiv e-prints
- Pub Date:
- June 2024
- DOI:
- 10.48550/arXiv.2406.04147
- arXiv:
- arXiv:2406.04147
- Bibcode:
- 2024arXiv240604147L
- Keywords:
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- Physics - Plasma Physics
- E-Print:
- Reviewers requested focusing on a single optimized configuration rather than three