DYNAMICS OF L-BIFURCATION 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 delP(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 EXB flow. This leads to a power threshold condition for the transition P(crit) almost-equal-to (munT)edge aRL(s).