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 hel iotron plasmas the mode becomes unstable in the edge region owing to the ma gnetic hill. However, for negative shear tokamaks, the resistive localized interchange mode becomes unstable where go is much larger than q(min), wher e go (q(min)) is the central (minimum) q value. With the appropriate ellipt icity and triangularity the stability against the resistive interchange mod e is significantly improved. It is also shown that ideal and resistive non resonant global interchange modes appear easily in the central region of he liotrons and in negative shear tokamaks; the modes are similar to the infer nal mode in low shear tokamaks.