Ideal and resistive interchange instabilities in negative shear tokamaks and currentless heliotron plasmas

For tokamaks the ideal localized interchange mode does not play a role for cases of q (safety factor) > 1 over the whole plasma region, whereas in heliotron plasmas the mode becomes unstable in the edge region owing to the magnetic hill. However, for negative shear tokamaks, the resistive localized interchange mode becomes unstable where q0 is much larger than qmin, where q0 (qmin) is the central (minimum) q value. With the appropriate ellipticity and triangularity the stability against the resistive interchange mode is significantly improved. It is also shown that ideal and resistive non-resonant global interchange modes appear easily in the central region of heliotrons and in negative shear tokamaks; the modes are similar to the infernal mode in low shear tokamaks.