Role of stable eigenmodes in saturated local plasma turbulence

Terry, P. W.; Baver, D. A.; Gupta, Sangeeta

doi:10.1063/1.2168453

Cited by 65 publications

(114 citation statements)

References 25 publications

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“…where given by a recurrence relation for the coefficients a n that reads (18) and is derived in the same way as the analogous recurrence relation in Ref. 5.…”

Section: -5mentioning

confidence: 99%

“…[12][13][14][15][16] Moreover, it has been shown recently that the interaction of unstable and stable eigenmodes at comparable scales facilitates turbulent saturation by providing an energy sink at the same scales as the energy drive. 10,[17][18][19] Thus, a careful study of both the unstable and stable parts of the linear eigenmode spectra is expected to lay the foundation for a deeper understanding of the saturation mechanisms which determine the level of heat transport in fusion plasmas.…”

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confidence: 99%

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Aspects of linear Landau damping in discretized systems

et al. 2013

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Discrete kinetic eigenmode spectra of electron plasma oscillations in weakly collisional plasma: A numerical study Phys. Plasmas 20, 012125 (2013) Non-planar ion-acoustic solitary waves and their head-on collision in a plasma with nonthermal electrons and warm adiabatic ions Phys. Plasmas 20, 012122 (2013) The incomplete plasma dispersion function: Properties and application to waves in bounded plasmas Phys. Plasmas 20, 012118 (2013) Effect of ion temperature on ion-acoustic solitary waves in a magnetized plasma in presence of superthermal electrons Phys. Plasmas 20, 012306 (2013) Additional information on Phys. Plasmas Basic linear eigenmode spectra for electrostatic Langmuir waves and drift-kinetic slab ion temperature gradient modes are examined in a series of scenarios. Collisions are modeled via a Lenard-Bernstein collision operator which fundamentally alters the linear spectrum even for infinitesimal collisionality [Ng et al., Phys. Rev. Lett. 83, 1974(1999. A comparison between different discretization schemes reveals that a Hermite representation is superior for accurately resolving the spectra compared to a finite differences scheme using an equidistant velocity grid. Additionally, it is shown analytically that any even power of velocity space hyperdiffusion also produces a Case-Van Kampen spectrum which, in the limit of zero hyperdiffusivity, matches the collisionless Landau solutions. V C 2013 American Institute of Physics. [http://dx

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“…where given by a recurrence relation for the coefficients a n that reads (18) and is derived in the same way as the analogous recurrence relation in Ref. 5.…”

Section: -5mentioning

confidence: 99%

mentioning

confidence: 99%

Aspects of linear Landau damping in discretized systems

et al. 2013

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“…Through this and other nonlinear processes, energy is transferred from linearly unstable modes (generally with small k x ) to stable modes at a variety of different wavenumbers, [161][162][163] saturating the turbulence and generally resulting in a wavenumber spectrum broad in both k x and k y . Therefore, if we want to test whether a given model is accurately capturing the nonlinear dynamics of the turbulence at an even deeper level than the frequency-based comparisons above allow, we should first examine the fidelity of the model in capturing this wavenumber spectrum.…”

Section: Fluctuation Comparisons Based On Spatial Correlation Propmentioning

confidence: 99%

Validation metrics for turbulent plasma transport

Holland

2016

Physics of Plasmas

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Developing accurate models of plasma dynamics is essential for confident predictive modeling of current and future fusion devices. In modern computer science and engineering, formal verification and validation processes are used to assess model accuracy and establish confidence in the predictive capabilities of a given model. This paper provides an overview of the key guiding principles and best practices for the development of validation metrics, illustrated using examples from investigations of turbulent transport in magnetically confined plasmas. Particular emphasis is given to the importance of uncertainty quantification and its inclusion within the metrics, and the need for utilizing synthetic diagnostics to enable quantitatively meaningful comparisons between simulation and experiment. As a starting point, the structure of commonly used global transport model metrics and their limitations is reviewed. An alternate approach is then presented, which focuses upon comparisons of predicted local fluxes, fluctuations, and equilibrium gradients against observation. The utility of metrics based upon these comparisons is demonstrated by applying them to gyrokinetic predictions of turbulent transport in a variety of discharges performed on the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)], as part of a multi-year transport model validation activity.

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“…For example, stable eigenmodes can often impact nonlinear dynamics by providing energy sinks and sometimes energy sources not found on the most unstable linear branch. [1][2][3][4][5][6][7][8][9][10] Stable eigenmodes can shift the energy injection and dissipation ranges, making the turbulent dynamics very different from the Kolmogorov picture of hydrodynamic turbulence. 11 Second, systems with non-normal modes (nonorthogonal eigenvectors) display properties that are unexpected from linear calculations.…”

Section: Introductionmentioning

confidence: 99%

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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Role of stable eigenmodes in saturated local plasma turbulence

Cited by 65 publications

References 25 publications

Aspects of linear Landau damping in discretized systems

Aspects of linear Landau damping in discretized systems

Validation metrics for turbulent plasma transport

Energy dynamics in a simulation of LAPD turbulence

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