Dynamics of L to H bifurcation

A self-consistent model of the L to H transition is derived from coupled nonlinear envelope equations for the fluctuation level, radial electric field shear E r ', and pressure gradient Del P i . These equations exhibit a bifurcation between dual L-mode and H-mode fixed points. They show that the L to H transition has similar characteristics to a phase transition of the second kind for which the order parameter is E r '. The transition occurs when the turbulence drive is large enough to overcome the damping of the E*B flow. This leads to a power threshold condition for the transition P crit approximately=( mu nT) edge aRL s .