Phase Space of Tokamak Edge Turbulence, theL−HTransition, and the Formation of the Edge Pedestal

Based on three-dimensional simulations of the Braginskii equations, we identify two main parameters which control transport in the edge of tokamaks: the MHD ballooning parameter and a diamagnetic parameter. The space defined by these parameters delineates regions where typical $L$-mode levels of transport arise, where the transport is catastrophically large (density limit) and where the plasma spontaneously forms a transport barrier ( $H$ mode).