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arXiv · 2102.12390

Ion-temperature-gradient stability near the magnetic axis of quasisymmetric stellarators

R. Jorge·M. Landreman
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Abstract

The stability of the ion-temperature gradient mode in quasisymmetric stellarators is assessed. This is performed using a set of analytical estimates together with linear gyrokinetic simulations. The peak growth rates, their corresponding real frequencies and wave-vectors are identified. A comparison is made between a first-order near-axis expansion model and eleven realistic designs obtained using numerical optimization methods. It is found that while the near-axis expansion is able to replicate the growth rates, real frequencies and perpendicular wave-vector at the inner core (both using simplified dispersion relations and first-principle gyrokinetic simulations), it leads to an overestimation of the growth rate at larger radii. An approximate analytic solution of the ITG dispersion relation for the non-resonant limit suggests growth rates could be systematically higher in quasi-axisymmetric (QA) configurations compared to quasi-helically (QH) symmetric ones. However except for very close to the axis, linear gyrokinetic simulations do not show systematic differences between QA and QH configurations.

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R. Jorge, M. Landreman. 2021-02-24. Ion-temperature-gradient stability near the magnetic axis of quasisymmetric stellarators. https://doi.org/10.1088/1361-6587%2Fabfdd4

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