Kinetic shooting code study of ballooning modes in a tokamak

The nature of the kinetic ballooning mode in the magnetohydrodynamic (MHD) second stability regime is clarified through the behaviour of the eigenfunction. It is found to be a continuation of the MHD ballooning mode (not of the second mode with a smaller growth rate which coexists with the MHD mode). The kinetic shooting code is also applied to the parameters of TFTR in which the kinetic ballooning mode has recently been observed. The toroidal mode number and the frequency for the fastest growing mode are found to be consistent with the experimental observations. Finite-beta stabilization of the electrostatic ion temperature gradient (ITG) mode and destabilization of the ITG-driven ballooning mode are demonstrated. Also studied is the mode stability in the negative shear region, where the MHD ballooning mode is known to be stable. The kinetic ballooning mode persists for s < O with a narrow stable window near null shear. (author)