Computation of electromagnetic turbulence and anomalous transport mechanisms in tokamak plasmas

Scott, B.

doi:10.1088/0741-3335/45/12a/025

Cited by 98 publications

(165 citation statements)

References 51 publications

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“…[21][22][23][24][25] Furthermore, the periodic axial boundary conditions used in the LAPD turbulence simulation are obviously unphysical, and more realistic boundary conditions may change the parallel dynamics disallowing an exact n 6 ¼ 0 $ n ¼ 0 path.…”

Section: Linear Versus Nonlinear Instability Drivementioning

confidence: 99%

“…They are after all, not essential to the otherwise similar nonlinear drift-like instabilities in the tokamak edge simulations. [21][22][23][24][25] Now, there are a few ways to eliminate the flute modes in the simulation, such as eliminating one of the nonlinearities that is essential to the nonlinear instability process described in Fig. 5.…”

Section: Linear Versus Nonlinear Instability Drivementioning

confidence: 99%

“…This has been explored in tokamak edge simulations in which linear ballooning instability drive is overtaken in the saturated phase by a nonlinear drift-wave drive. [21][22][23][24][25] Finally, it is often found that a particular linear instability is enhanced, depressed, and/or modified in the saturated phase by a nonlinear instability with a similar mechanism as the linear instability. In some of these cases, nonlinear wavenumber transfers can increase or cause drive, 26,27 while in other cases zonal flow effects decrease drive.…”

Section: Introductionmentioning

confidence: 99%

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Energy dynamics in a simulation of LAPD turbulence

et al. 2012

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Energy dynamics calculations in a 3D fluid simulation of drift wave turbulence in the linear Large Plasma Device [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875] illuminate processes that drive and dissipate the turbulence. These calculations reveal that a nonlinear instability dominates the injection of energy into the turbulence by overtaking the linear drift wave instability that dominates when fluctuations about the equilibrium are small. The nonlinear instability drives flutelike (k k ¼ 0) density fluctuations using free energy from the background density gradient. Through nonlinear axial wavenumber transfer to k k 6 ¼ 0 fluctuations, the nonlinear instability accesses the adiabatic response, which provides the requisite energy transfer channel from density to potential fluctuations as well as the phase shift that causes instability. The turbulence characteristics in the simulations agree remarkably well with experiment. When the nonlinear instability is artificially removed from the system through suppressing k k ¼ 0 modes, the turbulence develops a coherent frequency spectrum which is inconsistent with experimental data. This indicates the importance of the nonlinear instability in producing experimentally consistent turbulence. V C 2012 American Institute of Physics. [http://dx

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Section: Linear Versus Nonlinear Instability Drivementioning

confidence: 99%

Section: Linear Versus Nonlinear Instability Drivementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Energy dynamics in a simulation of LAPD turbulence

et al. 2012

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“…It can be regarded as one of the most intriguing results of half a century in physics of hot magnetized plasmas, that in macroscopically stable equilibria the confinement is nevertheless determined by micro-scale instabilities and fluctuations, with transport of energy and particles across magnetic flux surfaces being dominated by ubiquitous turbulence on small (gyro radius) scales and low (drift) frequencies [1,2,3,4,5,6,7]. This turbulence is regulated by the formation of mesoscopic zonal structures out of the turbulent flows [8,9,10,11,12,13].…”

Section: Introductionmentioning

confidence: 99%

Flux-surface shaping effects on tokamak edge turbulence and flows

Kendl

Scott

2006

Physics of Plasmas

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Shaping of magnetic flux surfaces is found to have a strong impact on turbulence and transport in tokamak edge plasmas. A series of axisymmetric equilibria with varying elongation and triangularity, and a divertor configuration are implemented into a computational gyrofluid turbulence model. The mechanisms of shaping effects on turbulence and flows are identified. Transport is mainly reduced by local magnetic shearing and an enhancement of zonal shear flows induced by elongation and X-point shaping.

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“…[44]. A single gyro-fluid microtearing simulation has also previously been reported [47], but with little discussion of the resulting turbulence characteristics and transport dependencies.…”

Section: Introductionmentioning

confidence: 99%

Simulation Of Microtearing Turbulence In NSTX

Guttenfelder¹,

Kaye²,

Nevins³

et al. 2012

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Thermal energy confinement times in NSTX dimensionless parameter scans increase with decreasing collisionality. While ion thermal transport is neoclassical, the source of anomalous electron thermal transport in these discharges remains unclear, leading to considerable uncertainty when extrapolating to future ST devices at much lower collisionality.Linear gyrokinetic simulations find microtearing modes to be unstable in high collisionality discharges. First non-linear gyrokinetic simulations of microtearing turbulence in NSTX show they can yield experimental levels of transport. Magnetic flutter is responsible for almost all the transport (~98%), perturbed field line trajectories are globally stochastic, and a test particle stochastic transport model agrees to within 25% of the simulated transport. Most significantly, microtearing transport is predicted to increase with electron collisionality, consistent with the observed NSTX confinement scaling. While this suggests microtearing modes may be the source of electron thermal transport, the predictions are also very sensitive to electron temperature gradient, indicating the scaling of the instability threshold is important. In addition, microtearing turbulence is susceptible to suppression via sheared E×B flows as experimental values of E×B shear (comparable to the linear growth rates) dramatically reduce the transport below experimental values. Refinements in numerical resolution and physics model assumptions are expected to minimize the apparent discrepancy. In cases where the predicted transport is strong, calculations suggest that a proposed polarimetry diagnostic may be sensitive to the magnetic perturbations associated with the unique structure of microtearing turbulence.

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Computation of electromagnetic turbulence and anomalous transport mechanisms in tokamak plasmas

Cited by 98 publications

References 51 publications

Energy dynamics in a simulation of LAPD turbulence

Energy dynamics in a simulation of LAPD turbulence

Flux-surface shaping effects on tokamak edge turbulence and flows

Simulation Of Microtearing Turbulence In NSTX

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