Zonal-Mean Atmospheric Dynamics of Slowly Rotating Terrestrial Planets
JOURNAL OF THE ATMOSPHERIC SCIENCES 76:5 (2019) 1397-1418
Isca, v1.0: a framework for the global modelling of the atmospheres of Earth and other planets at varying levels of complexity
GEOSCIENTIFIC MODEL DEVELOPMENT 11:3 (2018) 843-859
Collisionality scaling of the electron heat flux in ETG turbulence
Plasma Physics and Controlled Fusion IOP Publishing 59:5 (2017) 1-25
Abstract:In electrostatic simulations of MAST plasma at electron-gyroradius scales, using the local flux-tube gyrokinetic code GS2 with adiabatic ions, we find that the long-time saturated electron heat flux (the level most relevant to energy transport) decreases as the electron collisionality decreases. At early simulation times, the heat flux "quasi-saturates" without any strong dependence on collisionality, and with the turbulence dominated by streamer-like radially elongated structures. However, the zonal fluctuation component continues to grow slowly until much later times, eventually leading to a new saturated state dominated by zonal modes and with the heat flux proportional to the collision rate, in approximate agreement with the experimentally observed collisionality scaling of the energy confinement in MAST. We outline an explanation of this effect based on a model of ETG turbulence dominated by zonal-nonzonal interactions and on an analytically derived scaling of the zonal-mode damping rate with the electron-ion collisionality. Improved energy confinement with decreasing collisionality is favourable towards the performance of future, hotter devices.
Experimental signatures of critically balanced turbulence in MAST
Physical Review Letters 110:14 (2013)
Abstract:Beam emission spectroscopy (BES) measurements of ion-scale density fluctuations in the MAST tokamak are used to show that the turbulence correlation time, the drift time associated with ion temperature or density gradients, the particle (ion) streaming time along the magnetic field, and the magnetic drift time are consistently comparable, suggesting a "critically balanced" turbulence determined by the local equilibrium. The resulting scalings of the poloidal and radial correlation lengths are derived and tested. The nonlinear time inferred from the density fluctuations is longer than the other times; its ratio to the correlation time scales as ν*i-0. 8±0.1, where ν*i=ion â€Šâ €Šcollision â€Šâ€Šrate/streaming â€Šâ€Šrate. This is consistent with turbulent decorrelation being controlled by a zonal component, invisible to the BES, with an amplitude exceeding those of the drift waves by ∼ν*i-0.8. Published by the American Physical Society.
A key to improved ion core confinement in the JET tokamak: Ion stiffness mitigation due to combined plasma rotation and low magnetic shear
Physical Review Letters 107:13 (2011)