Mechanisms and dynamics of the external transport barrier formation in ă non-linear plasma edge simulations

International audienceL-H transition features are reproduced using three-dimensional ă first-principles plasma edge turbulence simulations. A transport barrier ă is observed to form spontaneously above a threshold of the input power. ă The physical mechanism relies on the coupling between the equilibrium ă pressure gradient and the poloidal flow, through both the radial force ă balance and the neoclassical friction. Accounting for the actual radial ă profile and time evolution of the latter is key to the barrier ă formation. It is found that neoclassical friction acts as an energy ă source for the flow, which largely overcomes the sink due to the ă turbulent Reynolds stress during the whole barrier lifetime. ă Importantly, experimentally reported dynamical features are recovered ă during the formation and lifetime of the barrier. This includes ă dithering of the radial electric field, which is reminiscent of ă experimentally observed limit-cycle oscillations and quasi-periodic ă relaxation oscillations showing similarities with type-III ELMs. These ă rich dynamics emerge from interplay between turbulence, ă turbulence-driven flows and the equilibrium flow governed by force ă balance