Generalized reduced MHD, and full MHD calculations with semi-implicit techniques

The Four-Field model of Hazeltine et al, generalizes the well-known reduced MHD (RMHD) equation to include parallel and perpendicular compressibility, diamagnetic drift frequencies, and pressure gradients in the parallel Ohm's law. This model is applied to the study of drift tearing modes in tokamaks; newly found Alfven resonant modes are discussed. Applications of recently developed semi-implicit techniques for efficient treatment of shear Alfven waves, ion sound waves, and semi-collisional terms are presented. Semi-implicit techniques are discussed in the context of non-reduced, full MHD equations also. Fully toroidal, linear and nonlinear studies of m = 1 modes in tokamaks are presented and discussed in terms of their application to fast saw-tooth crashes.