Confinement and bursty transport in a flux-driven convection model with sheared flows

Abstract

Transport and confinement within the resistive-g paradigm are investigated by means of two-dimensional numerical simulations. The system is driven by a constant incoming heat flux at the inner radial boundary. Different confinement and transport states are identified, involving self-sustained sheared poloidal flows. At the onset of turbulent convection the probability distribution functions of pressure and radial velocity fluctuations measured in the centre of the plasma layer have a nearly Gaussian form. Further increasing the heat flux drive these distributions become increasingly non-Gaussian, developing exponential tails. This large-scale intermittency is ascribed to the presence of bursting in the domain averaged convective transport and the fluctuation energy integrals. The quasi-periodic bursts are separated by shear-dominated quiescent periods in which the mean flow energy decreases and the confined heat increases on diffusive timescales. The time-averaged thermal energy confined within the plasma layer shows a power law dependence and significant increase with the injected power over the range of turbulent convection investigated.