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.

Reduced Lorenz models for anomalous transport and profile resilience

“…3 It has been pointed out by several authors that the RB instability has its counterpart in flute interchange instabilities in magnetized plasmas, driven unstable by pressure gradients in the direction of the radius of magnetic-field curvature. [4][5][6][7][8][9][10] In Sec. III, we explore this analogy in detail by deriving the RB and the Lorenz models for a particular interchange instability, and discussing the similarities and differences in the underlying physics.…”

Fluctuation-induced shear flow and energy transfer in plasma interchange turbulence

“…where represents the contribution of ion diamagnetic drift to the polarization current [3,4,[6][7][8], which is the crucial difference from the cold ion model [9][10][11][12][13][14][15][16][17][18][19]. The source terms S n and S E are added in Eqs.…”

“…The transfer of thermal energy to the E × B kinetic energy can be shown from Eqs. (5) and (6) in the absence of energy source and dissipation [6,10,11]. Integrating Eq.…”

“…Multiplying Eq. (9) by φ 0 and integrating over all space, one obtains the evolution of mean E × B flow energy [11] 1 2…”

“…The transfer of energy between fluctuations and sheared flows has also been demonstrated by fluid simulations for interchange turbulence with cold ions [10][11][12]. Recently, the formation of transport barrier has been simulated with fluid models [17][18][19], in which the neoclassical terms are added in the vorticity equation with cold ions.…”