Pressure and Inductance Effects on the Vertical Stability of Shaped Tokamaks

Numerical calculations are presented to show the influence of pressure and inductance on the vertical stability of shaped tokamaks. High values of epsilon beta(p) improve the vertical stability of dee shaped tokamaks but are destabilizing for an inverse dee. For elongated cross-sections, the pressure effect is well described by a linear dependence of the maximum value of the stable internal inductance l(i) on epsilon beta(p), with a coefficient that depends on the geometry and increases with the triangularity. Stability diagrams are shown in terms of l(i) versus epsilon beta(p) for TCV- and DIII-D-like cross-sections. Current profile effects depend critically on the wall configuration: low values of l(i) are stabilizing if the wall is close, but increase the driving farce of the instability in the absence of a wall. The competition between these two effects is considered for a configuration with discrete external conductors.