MHD stability analysis by revised version of ERATO-J

The linear ideal MHD stability analysis code ERATO-J has been improved in the following four problems. (i) The high accuracy mapping module is developed, which guarantees the convergence of eigenvalues to be smooth and quadratic with respect to the mesh number. (ii) The quasi-mode representation is added, which is essential to analyses of middle and high n mode stabilities. (iii) The vector potential method in the calculation of the vacuum energy is applied in place of the Green function method (GFM), which removes the singularity in the GFM and also included the effect of the axisymmetric mode. (iv) The packing technique for the large scale sparse matrix is used to solve the generalized eigenvalue problem by the inverse iteration, which reduces the necessary disk files, I/O accesses, and CPU time. By using this revised version of ERATO-J code, the n = 1 internal kink mode and ballooning modes are studied. The second stability region against the n = 1 internal kink mode is found. The dependence of the growth rate of ballooning modes on the toroidal mode number n and shear is clarified. (author)