TEARING MODE ANALYSIS IN TOKAMAKS, REVISITED

A new Delta ' shooting code has been developed to investigate tokamak plasma tearing mode stability in a cylinder and large aspect ratio (ep silon less than or equal to 0.25) toroidal geometries, neglecting toro idal mode coupling. A different computational algorithm is used (shoot ing out from the singular surface instead of into it) to resolve the s trong singularities at the mode rational surface, particularly in the presence of the finite pressure term. Numerical results compare favora bly with Furth et al. [H. P. Furth et al., Phys. Fluids 16, 1054 (1973 )] results. The effects of finite pressure, which are shown to decreas e Delta ', are discussed. It is shown that the distortion of the flux surfaces by the Shafranov shift, which modifies the geometry metric el ements, stabilizes the tearing mode significantly, even in a low-beta regime before the toroidal magnetic curvature effects come into play. (C) 1998 American Institute of Physics. [S1070-664X(98)02812-2].