Impact of shaping on microstability in high-performance tokamak plasmas

Journal article

We have used the local-δf gyrokinetic code GS2 to perform studies of the effect of flux-surface shaping on two highly-shaped, low- and high-β JT-60SA-relevant equilibria, including a successful benchmark with the GKV code. We find that for a high-performance plasma, i.e. one with high plasma beta and steep pressure gradients, the turbulent outwards radial fluxes may be reduced by minimizing the elongation. 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 β, increased elongation degrades the local magnetic shear stabilization that enables access to the region of ballooning second-stability.

Authors: Beeke, O; Barnes, M; Romanelli, M; Nakata, M; Yoshida, M

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: IOP Publishing
• Journal: Nuclear Fusion
• Volume: 61
• Issue: 6
• Article number: 66020
• Publication date: 2021-05-04
• Acceptance date: 2021-04-09
• DOI: 10.1088/1741-4326/abf660
• EISSN: 1741-4326
• ISSN: 0029-5515
• Language: English
• Keywords: turbulence; shaping; gyrokinetics; FFR