MHD Instabilities in Toroidal Helical Systems

MHD instabilities in toroidal herical systems based on theory and reduced MHD equations by assuming the stellarator expansion are discussed. This approach sabrifices some physics compared to the three-dimensional culculation using the full MHD equations, but the improved resolution and computational speed offer a better understanding to explore the large parameeter space. The experimental results concerning MHD instabilities could be explained by the reduced MHD equations. Investigation of nonlinear evolution for the unstable mode can be pursued straightforwardly.