On secondary and tertiary instability in electromagnetic plasma microturbulence

Pueschel, M. J.; Görler, T.; Jenko, F.; Hatch, D. R.; Cianciara, A. J.

doi:10.1063/1.4825227

Cited by 36 publications

(42 citation statements)

References 51 publications

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“…The correlation of the nonlinear EM-stabilization and increased destabilization of ZF secondaries has been reported [13]. This connection is verified in these simulations as well.…”

Section: Nonlinear Simulations At ρ = 033supporting

confidence: 71%

Electromagnetic stabilization of tokamak microturbulence in a high-βregime

Citrin

García

Görler

et al. 2014

Plasma Phys. Control. Fusion

146

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The impact of electromagnetic stabilization and flow shear stabilization on ITG turbulence is investigated. Analysis of a low-β JET L-mode discharge illustrates the relation between ITG stabilization, and proximity to the electromagnetic instability threshold. This threshold is reduced by suprathermal pressure gradients, highlighting the effectiveness of fast ions in ITG stabilization. Extensive linear and nonlinear gyrokinetic simulations are then carried out for the high-β JET hybrid discharge 75225, at two separate locations at inner and outer radii. It is found that at the inner radius, nonlinear electromagnetic stabilization is dominant, and is critical for achieving simulated heat fluxes in agreement with the experiment. The enhancement of this effect by suprathermal pressure also remains significant. It is also found that flow shear stabilization is not effective at the inner radii. However, at outer radii the situation is reversed. Electromagnetic stabilization is negligible while the flow shear stabilization is significant. These results constitute the high-β generalization of comparable observations found at low-β at JET. This is encouraging for the extrapolation of electromagnetic ITG stabilization to future devices. An estimation of the impact of this effect on the ITER hybrid scenario leads to a 20% fusion power improvement.

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“…The correlation of the nonlinear EM-stabilization and increased destabilization of ZF secondaries has been reported [13]. This connection is verified in these simulations as well.…”

Section: Nonlinear Simulations At ρ = 033supporting

confidence: 71%

Electromagnetic stabilization of tokamak microturbulence in a high-βregime

Citrin

García

Görler

et al. 2014

Plasma Phys. Control. Fusion

146

View full text Add to dashboard Cite

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“…Secondary instability describes the tendency for a "primary" eigenmode to be unstable to a perturbation and its sidebands. [31][32][33][34][35] It has been shown that the dispersion relation of a primary eigenmode to a secondary zonal flow is identical to the dispersion relation of zonostrophic instability in the appropriate limit. 36 Thus, the zonostrophic instability can be thought of as a generalized modulational instability whereby an entire fluctuation spectrum is unstable to a regular coherent structure.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation of the geometrical-optics reduction of CE2 and comparisons to quasilinear dynamics

Parker

2018

Physics of Plasmas

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Zonal flows have been observed to appear spontaneously from turbulence in a number of physical settings. A complete theory for their behavior is still lacking. Recently, a number of studies have investigated the dynamics of zonal flows using quasilinear theories and the statistical framework of a second-order cumulant expansion (CE2). A geometrical-optics (GO) reduction of CE2, derived under an assumption of separation of scales between the fluctuations and the zonal flow, is studied here numerically. The reduced model, CE2-GO, has a similar phase-space mathematical structure to the traditional wave-kinetic equation, but that wave-kinetic equation has been shown to fail to preserve enstrophy conservation and to exhibit an ultraviolet catastrophe. CE2-GO, in contrast, preserves nonlinear conservation of both energy and enstrophy. We show here how to retain these conservation properties in a pseudospectral simulation of CE2-GO. We then present nonlinear simulations of CE2-GO and compare with direct simulations of quasilinear (QL) dynamics. We find that CE2-GO retains some similarities to QL. The partitioning of energy that resides in the zonal flow is in good quantitative agreement between CE2-GO and QL. On the other hand, the length scale of the zonal flow does not follow the same qualitative trend in the two models. Overall, these simulations indicate that CE2-GO provides a simpler and more tractable statistical paradigm than CE2, but CE2-GO is missing important physics.

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“…The full details of this new theory -along with a discussion of the underlying physics -will be presented in a separate paper, while here, additional details and background information with regard to the corresponding numerical setup are given. Note that the present work focuses only on the erosion of zonal flows, whereas a study of the finite-β properties of their nonlinear drive has been relegated to a separate publication [24]-it suffices to stress here that no impact of (moderately) changed zonal flow drive on the NZT is to be expected.…”

Section: Zonal Flows and Magnetic Fluctuationsmentioning

confidence: 99%

“…As a baseline resolution, (N x , N ky , N z , N v , N µ ) = (192,24,24,48,8) was used which results in well-converged simulations (where convergence is measured in different transport channels, including the electron magnetic channel) for the parameters in Ref. [12].…”

Section: Numerical Framework and Convergencementioning

confidence: 99%