Global Theory of Microtearing Modes in the Tokamak Pedestal.

The pedestal of H-mode tokamaks displays strong magnetic fluctuations correlated with the evolution of the electron temperature. The microtearing mode (MTM), a temperature-gradient-driven instability that alters magnetic topology, is compatible with these observations. Here we extend the conventional theory of the MTM to include the global variation of the temperature and density profiles. The offset between the rational surface and the location of the pressure gradient maximum (µ) emerges as a crucial parameter for MTM stability. The extended theory matches observations on the Joint European Torus tokamak.