scholarly journals On the nature of radial transport across sheared zonal flows in electrostatic ion-temperature-gradient gyrokinetic tokamak plasma turbulence

2009 ◽  
Vol 16 (5) ◽  
pp. 055905 ◽  
Author(s):  
R. Sánchez ◽  
D. E. Newman ◽  
J.-N. Leboeuf ◽  
B. A. Carreras ◽  
V. K. Decyk
Keyword(s):  
Temperature Gradient ◽  
Plasma Turbulence ◽  
Tokamak Plasma ◽  
Ion Temperature ◽  
Radial Transport ◽  
Ion Temperature Gradient ◽  
Zonal Flows

scholarly journals Enstrophy non-conservation and the forward cascade of energy in two-dimensional electrostatic magnetized plasma turbulence

2020 ◽  
Vol 86 (4) ◽  
Author(s):  
G. G. Plunk
Keyword(s):  
Temperature Gradient ◽  
Plasma Turbulence ◽  
Magnetized Plasma ◽  
Larmor Radius ◽  
Ion Temperature ◽  
Fluid System ◽  
Ion Temperature Gradient ◽  
Zonal Flows ◽  
Electron Temperature Gradient ◽  
Enstrophy Cascade

A fluid system is derived to describe electrostatic magnetized plasma turbulence at scales somewhat larger than the Larmor radius of a given species. It is related to the Hasegawa–Mima equation, but does not conserve enstrophy, and, as a result, exhibits a forward cascade of energy, to small scales. The inertial-range energy spectrum is argued to be shallower than a $-11/3$ power law, as compared to the $-5$ law of the Hasegawa–Mima enstrophy cascade. This property, confirmed here by direct numerical simulations of the fluid system, may help explain the fluctuation spectrum observed in gyrokinetic simulations of streamer-dominated electron-temperature-gradient driven turbulence (Plunk et al., Phys. Rev. Lett., vol. 122, 2019, 035002), and also possibly some cases of ion-temperature-gradient driven turbulence where zonal flows are suppressed (Plunk et al., Phys. Rev. Lett., vol. 118, 2017, 105002).

Zonal flows and transport in ion temperature gradient turbulence

2002 ◽  
Vol 9 (12) ◽  
pp. 4911-4916 ◽  
Author(s):  
Sheikh Dastgeer ◽  
Sangeeta Mahajan ◽  
Jan Weiland
Keyword(s):  
Temperature Gradient ◽  
Ion Temperature ◽  
Ion Temperature Gradient ◽  
Zonal Flows

scholarly journals Transition to subcritical turbulence in a tokamak plasma

2016 ◽  
Vol 82 (6) ◽  
Author(s):  
F. van Wyk ◽  
E. G. Highcock ◽  
A. A. Schekochihin ◽  
C. M. Roach ◽  
A. R. Field ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Initial Perturbation ◽  
Outer Core ◽  
Transition To Turbulence ◽  
Tokamak Plasma ◽  
Ion Temperature ◽  
Flow Shear ◽  
Ion Temperature Gradient ◽  
Stability Threshold ◽  
Accretion Flows

Tokamak turbulence, driven by the ion-temperature gradient and occurring in the presence of flow shear, is investigated by means of local, ion-scale, electrostatic gyrokinetic simulations (with both kinetic ions and electrons) of the conditions in the outer core of the Mega-Ampere Spherical Tokamak (MAST). A parameter scan in the local values of the ion-temperature gradient and flow shear is performed. It is demonstrated that the experimentally observed state is near the stability threshold and that this stability threshold is nonlinear: sheared turbulence is subcritical, i.e. the system is formally stable to small perturbations, but, given a large enough initial perturbation, it transitions to a turbulent state. A scenario for such a transition is proposed and supported by numerical results: close to threshold, the nonlinear saturated state and the associated anomalous heat transport are dominated by long-lived coherent structures, which drift across the domain, have finite amplitudes, but are not volume filling; as the system is taken away from the threshold into the more unstable regime, the number of these structures increases until they overlap and a more conventional chaotic state emerges. Whereas this appears to represent a new scenario for transition to turbulence in tokamak plasmas, it is reminiscent of the behaviour of other subcritically turbulent systems, e.g. pipe flows and Keplerian magnetorotational accretion flows.

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