Calculation of resistive magnetohydrodynamic spectra in tokamaks

Resistive magnetohydrodynamic spectra of toroidal plasmas are calculated us ing the recently developed Jacobi-Davidson eigenvalue solver. Poloidal mode coupling in finite aspect ratio tokamaks yields gaps in the ideal Alfven c ontinuous spectrum. If resistivity is included, the ideal continua disappea r and are replaced by damped global waves located on specific curves in the complex frequency plane. The end points of these curves join the tips of t he ideal continua and the boundaries of the ideal spectral gap. The eigenfu nctions of the waves on these resistive curves are shown to have definite p arity in the poloidal harmonics. It is shown that for very small toroidicit y the topology of the resistive spectrum is completely different from the c ylindrical one. Independent of the size of the inverse aspect ratio the ide al gap remains visible in the resistive spectrum. (C) 1999 American Institu te of Physics. [S1070-664X(99)01805-4].