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arXiv · 2012.02669

Impact of plasma shaping on tokamak microstability

O. Beeke·M. Barnes·M. Romanelli·M. Nakata·M. Yoshida
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Abstract

We have used the local-$\delta{f}$ gyrokinetic code GS2 to perform studies of the effect of flux-surface shaping on two highly-shaped, low- and high-$\beta$ JT-60SA-relevant equilibria, including a successful benchmark with the GKV code. We find a novel destabilization of electrostatic fluctuations with increased elongation for plasma with a strongly peaked pressure profile. We explain the results as a competition between the local magnetic shear and finite-Larmor-radius (FLR) stabilization. Electromagnetic studies indicate that kinetic ballooning modes are stabilized by increased shaping due to an increased sensitivity to FLR effects, relative to the ion-temperature-gradient instability. Nevertheless, at high enough $\beta$, increased elongation degrades the local magnetic shear stabilization that enables access to the region of ballooning second-stability.

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O. Beeke, M. Barnes, M. Romanelli, M. Nakata, M. Yoshida. 2020-12-04. Impact of plasma shaping on tokamak microstability. https://arxiv.org/abs/2012.02669

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