Plasma current and its profile affect ideal MHD stability properties through changing magnetic well and shear besides destabilizing current-driven modes. Since the role of bootstrap current in quasi-axisymmetric (QA) configurations is more important than that in conventional ones, ideal MHD stability analysis including plasma current is essential for exploring beta limit and avoiding serious instabilities in the physics design of such devices. In this study we have investigated effects of current profile on ideal MHD stability properties in a QA stellarator CHS-qa proposed as a candidate for the next compact helical device in Japan.
The analyses are based on VMEC equilibria calculated for CHS-qa reference configurations followed by subsequent investigation of global low-n and local ballooning modes. Self-consistent bootstrap current is estimated by SPBSC code whose validity has been demonstrated experimentally. We have mainly used TERPSICHORE[1] and CAS3D[2] codes as three-dimensional numerical tools for MHD analyses. Assuming reasonable density and temperature profiles, beta limit for low-n mode of an equilibrium with bootstrap current is at least higher than 3% without tailoring pressure profiles.
Considering the possibility of controlling current profile by beam-driven or ohmic currents, we have also carried out the analyses of CHS-qa equilibria with changing rotational transform profiles artificially. As a result, it has been shown that values of edge rotational transform play a crucial role in triggering external kink modes. More detailed survey of various current profiles and possibility of avoiding instabilities by controlling plasma current profile will be discussed.

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