Interchange-Ballooning Mode in l = 2 Helical Systems

A high shear toroidal helical system such as Heliotron E gives a limiting beta comparable to tokamaks, by examining stability against interchange-ballooning modes with a low toroidal mode number. The limiting beta depends on equilibrium pressure profiles and a high beta value is found for the pressure having a flat profile in the central region and a large pressure gradient at the high shear peripheral region of the plasma column.