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arXiv · 2212.01143

A quasi-isodynamic configuration with good confinement of fast ions at low plasma $\beta$

E. Sánchez·J. L. Velasco·I. Calvo·S. Mulas
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Abstract

A new quasi-isodynamic stellarator configuration optimized for the confinement of energetic ions at low plasma $\beta$ is obtained. The numerical optimization is carried out using the STELLOPT suite of codes. New proxies to measure closeness to quasi-isodynamicity and quality of fast ion confinement have been included. The new configuration has poloidally closed contours of magnetic field strength, low magnetic shear and a rotational transform profile allowing an island divertor. It shows ideal and ballooning magnetohydrodynamic stability up to $\beta = 5%$, reduced effective ripple, with $\epsilon_{eff} < 0.5%$ in the plasma core. Even at low $\beta$, the configuration approximately satisfies the maximum-$J$ property, and the confinement of fast ions is good at $\beta \sim 1.5%$ and becomes excellent at reactor values, $\beta \sim 4%$. An evaluation of the $D_{31}$ neoclassical mono-energetic coefficient supports the expectation of a reduced bootstrap current for plasmas confined in quasi-isodynamic configurations. A set of filamentary coils that preserve the good confinement of fast ions in the core is presented.

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E. Sánchez, J. L. Velasco, I. Calvo, S. Mulas. 2022-12-02. A quasi-isodynamic configuration with good confinement of fast ions at low plasma $\beta$. https://doi.org/10.1088/1741-4326%2Faccd82

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