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arXiv · 2303.06038

Higher order theory of quasi-isodynamicity near the magnetic axis of stellarators

Eduardo Rodriguez·Gabe G. Plunk
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Abstract

The condition of quasi-isodynamicity is derived to second order in the distance from the magnetic axis. We do so using a formulation of omnigenity that explicitly requires the balance between the radial particle drifts at opposite bounce points of a magnetic well. This is a physically intuitive alternative to the integrated condition involving distances between bounce points, used in previous works. We investigate the appearance of topological defects in the magnetic field strength (``puddles''). A hallmark of quasi-isodynamic fields, the curved contour of minimum field strength, is found to be inextricably linked to these defects. Our results pave the way to constructing solutions that satisfy omnigenity to a higher degree of precision, and also to simultaneously consider other physical properties, like shaping and stability.

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Eduardo Rodriguez, Gabe G. Plunk. 2023-03-10. Higher order theory of quasi-isodynamicity near the magnetic axis of stellarators. https://doi.org/10.1063/5.0150275

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