A theory for magnetic braiding in toroidal plasmas, which is caused by microscopic pressure-gradient-driven turbulence, is developed. The balance between nonlinear destabilization and nonlinear stabilization is solved analytically for the case of interchange mode turbulence. It is found that, when the pressure gradient exceeds a threshold value, the magnetic braiding and enhanced anomalous transport become self-sustaining. Enhancements of the thermal conductivity and magnetic perturbation amplitude, as well as the threshold pressure gradient, are obtained. A cusp-type catastrophe in the thermal conductivity is predicted. The bifurcation associated with the abrupt burst of magnetic perturbations is predicted to occur when the pressure gradient reaches a critical value.
Intrinsic suppression of turbulence in linear plasma devices