Nonlinear studies of m = 1 modes in high-temperature plasmas

Abstract

Nonlinear evolution of the m=1 mode is examined in high‐temperature plasmas where the mode is in the semicollisional or collisionless regime. Unlike the finite −Δ’(m≥2) tearing modes, the nonlinear evolution of which is collisional, both the semicollisional and collisionless m=1 modes exhibit nonlinearly enhanced growth rates that far exceed their linear values, thus making their nonlinear evolution collisionless; this accelerated growth of a collisionless m=1 mode may explain the fast sawtooth crashes observed in large tokamaks.