STABILIZATION OF COLLISIONAL DRIFT-TEARING MODES AT THE BREAKDOWN OF THE CONSTANT-PSI APPROXIMATION

The linear growth rate of the collisional drift-tearing mode is found to be a nonmonotonic function of the stability parameter DELTA'. It reaches a maximum for DELTA' almost-equal-to 0.5-DELTA-1' = m-omega-A/square-root omega-triple-overdot *e(omega-triple-overdot *e - omega-di) > 0, where omega-A, omega-triple-overdot *e, omega-di are the Alfven, electron drift wave, and ion diamagnetic frequencies, and becomes negative for DELTA' greater-than-or-equal-to DELTA-1', corresponding to the regime where the constant-PSI approximation breaks down. A second mode, identified as the diamagnetic modification of the epsilon-eta-1/3 mode near the condition for ideal magnetohydrodynamic (MHD) marginal stability, becomes unstable for DELTA' greater-than-or-equal-to DELTA-2' = (omega-triple-overdot *e/omega-A-epsilon-eta)1/2 > DELTA-1', leaving a stable window in values of DELTA'. Applications to the stability of modes with poloidal and toroidal mode numbers m = n = 1 are presented.