Fluctuation level bursts in a model of internal transport barrier formation

A model of internal transport barriers ~ITB! is developed that, in addition to the typical features of ITB models ~the phase transition character with a power threshold, barrier front propagation, etc.!, exhibits an oscillatory/bursty behavior close to the transition. This behavior comes from the competition between the driving and suppression mechanisms for the turbulence. The onset of the oscillations has a power threshold, Posc , below the power threshold for the transition to the enhanced confinement regime, P th . In the calculations, Posc;0.5P th . This suggests that the oscillations avoid an early transition at P th5Posc , so any mechanism that eliminates the oscillations may lower the transition power. © 1999 American Institute of Physics. @S1070-664X~99!00903-9#