Abstract
The collapse mechanism of internal transport barrier in reversed magnetic shear configuration is investigated using multi-scale global simulation code for ion temperature gradient driven drift wave turbulence with a heat source term. In the simulation, the transport remains at the neoclassical level around the q-minimum region, on the other hand, far from q-minimum region the turbulence develops. As the result, a kind of internal transport barrier is observed. A meso-scale mode plays essential role for the decay of the transport barrier. The energy source channels supplying energy to the meso-scale mode are analyzed. It is confirmed that such mode is excited via three-wave coupling initially. After that, the contribution from the quasi-linear channel increases gradually. The modification of the temperature profile gives rise to the excitation of the ion temperature gradient driven mode at the outside edge of the transport barrier and it triggers the collapse.
