Effects of non-circular tokamak geometry on ion-temperature-gradient driven modes

The influence of plasma elongation and Shafranov shift on the stability of electrostatic ion-temperature-gradient driven modes (eta(i)-modes) is inves tigated. An advanced fluid model is used for the ions together with Boltzma nn distributed electrons. The derived eigenvalue equation is solved both an alytically, in the strong ballooning limit, and numerically. It is found th at the effects of elongation change from stabilizing, for peaked density pr ofiles, to destabilizing in the Rat density regime. In addition, it is show n that the maximum growth rate is shifted towards shorter wavelengths as th e elongation increases. The effects of shaping on tokamak stability are exe mplified with data from a Joint European Torus (JET) high-performance mode discharge.