Nonlinear entropy transfer via zonal flows in gyrokinetic plasma turbulence

Nakata, M.; Watanabe, T.‐H.; Sugama, H.

doi:10.1063/1.3675855

Cited by 64 publications

(90 citation statements)

References 33 publications

(67 reference statements)

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“…The zonal flows, which are more efficiently generated by the neoclassical optimized configuration, are considered to induce the spectral transfer via the nonlinear entropy transfer. 29 The same analyses as in Ref. 29, which are not demonstrated in the present paper, can be done to directly show the effects of the zonal flows on the spectral transfer in the k x direction.…”

Section: -5 Nunami Et Almentioning

confidence: 97%

“…29 The same analyses as in Ref. 29, which are not demonstrated in the present paper, can be done to directly show the effects of the zonal flows on the spectral transfer in the k x direction. Detailed results of the spectral transfer analyses will be reported in a separate work.…”

Section: -5 Nunami Et Almentioning

confidence: 97%

“…The spectral transfer is considered to be induced through the interaction between zonal flows and turbulence as discussed in Ref. 29. The high-k x modes in the spreading spectrum make less contribution to the transport while they still contribute to the integrated power spectrum shown in Fig.…”

Section: -3 Nunami Et Almentioning

confidence: 99%

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Gyrokinetic turbulent transport simulation of a high ion temperature plasma in large helical device experiment

et al. 2012

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Ion temperature gradient turbulent transport in the large helical device (LHD) is investigated by means of gyrokinetic simulations in comparison with the experimental density fluctuation measurements of ion-scale turbulence. The local gyrokinetic Vlasov simulations are carried out incorporating full geometrical effects of the LHD configuration, and reproduce the turbulent transport levels comparable to the experimental results. Reasonable agreements are also found in the poloidal wavenumber spectra of the density fluctuations obtained from the simulation and the experiment. Numerical analysis of the spectra of the turbulent potential fluctuations on the two-dimensional wavenumber space perpendicular to the magnetic field clarifies the spectral transfer into a high radial wavenumber region which correlates with the regulation of the turbulent transport due to the zonal flows. The resultant transport levels at different flux surfaces are expressed in terms of a simple linear relation between the transport coefficient and the ratio of the squared turbulent potential fluctuation to the averaged zonal flow amplitude. V C 2012 American Institute of Physics. [http://dx

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Section: -5 Nunami Et Almentioning

confidence: 97%

Section: -5 Nunami Et Almentioning

confidence: 97%

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Gyrokinetic turbulent transport simulation of a high ion temperature plasma in large helical device experiment

et al. 2012

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“…In the electrostatic limit (A → 0), the transfer function is reduced to that in Nakata et al (2012). The transfer function satisfies the detailed balance equation,…”

Section: Conserved Quantitiesmentioning

confidence: 99%

Electromagnetic gyrokinetic simulation of turbulence in torus plasmas

et al. 2015

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Gyrokinetic simulations of electromagnetic turbulence in magnetically confined torus plasmas including tokamak and heliotron/stellarator are reviewed. Numerical simulation of turbulence in finite beta plasmas is an important task for predicting the performance of fusion reactors and a great challenge in computational science due to multiple spatio-temporal scales related to electromagnetic ion and electron dynamics. The simulation becomes further challenging in non-axisymmetric plasmas. In finite beta plasmas, magnetic perturbation appears and influences some key mechanisms of turbulent transport, which include linear instability and zonal flow production. Linear analysis shows that the ion-temperature gradient (ITG) instability, which is essentially an electrostatic instability, is unstable at low beta and its growth rate is reduced by magnetic field line bending at finite beta. On the other hand, the kinetic ballooning mode (KBM), which is an electromagnetic instability, is destabilized at high beta. In addition, trapped electron modes (TEMs), electron temperature gradient (ETG) modes, and micro-tearing modes (MTMs) can be destabilized. These instabilities are classified into two categories: ballooning parity and tearing parity modes. These parities are mixed by nonlinear interactions, so that, for instance, the ITG mode excites tearing parity modes. In the nonlinear evolution, the zonal flow shear acts to regulate the ITG driven turbulence at low beta. On the other hand, at finite beta, interplay between the turbulence and zonal flows becomes complicated because the production of zonal flow is influenced by the finite beta effects. When the zonal flows are too weak, turbulence continues to grow beyond a physically relevant level of saturation in finite-beta tokamaks. Nonlinear mode coupling to stable modes can play a role in the saturation of finite beta ITG mode and KBM. Since there is a quadratic conserved quantity, evaluating nonlinear transfer of the conserved quantity from unstable modes to stable modes is useful for understanding the saturation mechanism of turbulence.

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“…Since turbulence clearly cannot be saturated by linear physics alone, this means that our estimate does not capture the correct nonlinear time. We conjecture that it is in fact the coupling to the zonal flows, invisible to BES (because their δn = 0), that dominates over the nonlinear interaction between the drift-wave-like fluctuations represented by τ NZ nl [38,[40][41][42][43][44][45][46]. It has long been suspected that the relative amplitude of the zonal flows compared to that of the drift waves depends on the ion collisionality [38,[47][48][49].…”

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Experimental Signatures of Critically Balanced Turbulence in MAST

et al. 2013

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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 −0.8±0.1 * i , where ν * i = ion collision rate/streaming rate. This is consistent with turbulent decorrelation being controlled by a zonal component, invisible to the BES, with an amplitude exceeding the drift waves' by ∼ ν −0.8 * i .Introduction. Microscale turbulence hindering energy confinement in magnetically confined hot plasmas is driven by gradients of equilibrium quantities such as temperature and density. These gradients give rise to instabilities that inject energy into plasma fluctuations ("drift waves") at scales just above the ion Larmor scale. The most effective of these is believed to be the iontemperature-gradient (ITG) instability [1][2][3]. A turbulent state ensues, giving rise to "anomalous transport" of energy [4]. It is of interest, both for practical considerations of improving confinement and for the fundamental understanding of multiscale plasma dynamics, what the structure of this turbulence is and how its amplitude, scale(s) and resulting transport depend on the equilibrium parameters: ion and electron temperatures, density, angular velocity, magnetic geometry, etc.Fluctuations in a magnetized toroidal plasma are subject to a number of distinct physical effects, which can be thought about in terms of various time scales such as the drift times associated with the temperature and density gradients, the particle streaming time along the magnetic field as it takes them around the torus toroidally and poloidally, the magnetic (∇B and curvature) drift times of particles moving across the field, the nonlinear time of the fluctuations being advected across the field by the fluctuating E × B velocity, the time between collisions, the shear time associated with plasma rotation. Some of these time scales and, consequently, the corresponding physics may be irrelevant, while others play a crucial role for the saturation of the linearly unstable fluctuations. There has been a growing understanding [5], driven largely by theory [6][7][8][9], observations [10][11][12] and simulations of magnetohydrodynamic [13][14][15] and kinetic [7,16] plasma turbulence in space, that if a medium can

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Nonlinear entropy transfer via zonal flows in gyrokinetic plasma turbulence

Cited by 64 publications

References 33 publications

Gyrokinetic turbulent transport simulation of a high ion temperature plasma in large helical device experiment

Gyrokinetic turbulent transport simulation of a high ion temperature plasma in large helical device experiment

Electromagnetic gyrokinetic simulation of turbulence in torus plasmas

Experimental Signatures of Critically Balanced Turbulence in MAST

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