Behavior of interchange mode in heliotron and tokamak

When the pressure profile becomes flat locally at the resonant surface, the beta limit due to the ideal interchange mode increases, since the highly localized radial mode structure is suppressed. It is also found that non-resonant ideal modes become unstable near the magnetic axis, when the pressure profile is highly peaked in Heliotron E. However, the beta limit of non-resonant mode is higher than that of resonant mode. On the other hand for negative shear tokamaks, resistive interchange modes are destabilized, when q0 (q value at magnetic axis) is larger than qmin (minimum q value). Here the nonresonant ideal modes similar to those in Heliotron E also become unstable. (author)