SELF-REGULATING SHEAR-FLOW TURBULENCE - A PARADIGM FOR THE L TO H TRANSITION

A self-consistent model of the L to H transition is derived from coupled nonlinear envelope equations for the fluctuation level and radial electric field shear E(r)'. These equations exhibit a supercritical bifurcation between dual L-mode and H-mode fixed points. The transition occurs when the turbulence level is large enough for the Reynolds stress drive to overcome the damping of the E x B flow. This defines a power threshold for the transition, which is calculated and found to be consistent with experimental findings.