Analysis of MHD stability in high-β plasmas in LHD

Up to now, theoretically idealized MHD equilibria reflecting experimental conditions have been used in order to examine the ideal MHD stability. This approach has been useful from the aspect of investing general properties of the ideal MHD stability. Since the properties of a three dimensional MHD equilibrium with large Shafranov shift significantly change by the pressure profile, the current profile, and the boundary condition, however, ideal MHD stability analysis based on theoretically idealized MHD equilibria is considered not to be enough to investigate the proper MHD ability of experimentally obtained MHD equilibria. Indeed, it is shown that ideal MHD stability based on the realistic reconstructed MHD equilibrium with fine structures is different from that based on the theoretically idealized MHD equilibrium. Especially, it is firstly reported that high-n ballooning modes are destabilized in the magnetic well region with tokamak-like magnetic shear. (author)