Abstract: Three-point center difference scheme is employed to solve tearing mode equations which have the second-order removing singularity at an interval end and the first-order non-removing sigularity on the rational magnetic surface in the interval. A method of approximately equivalent grids is presented. The numerical simulations of the tearing mode equations with toroidal coupling are done under different safety factor distributions, and give the corresponding link parameters which can determine the stability of the mode, coupling intensity parameters, growing factors. These numerical results show that the toroidal coupling effect in linear stage has a little influence.

Key words: Tearing Mode Equations, Difference Scheme, Approximately equivalent Grids