The ideal-MHD stability properties of a special class of vertically asymmetric tokamak equilibria, with the plasma boundary a rotated ellipse, are examined. The calculations confirm that no major new physical effects are introduced and the modifications can be understood by conventional arguments. The results indicate that significant departures from up-down symmetry can be tolerated before the reduction in β becomes important for reactor operation. They show that the second stable region for internal modes can be extended to low-n modes and small-aspect-ratio devices by rotating the cross-section from a standing ellipse.
Ideal- and resistive-MHD stability of one-dimensional tokamak equilibria