Turbulence suppression in the neighbourhood of a minimum-<i>q</i>surface due to zonal flow modification in reversed shear tokamaks

Miyato, N.; Kishimoto, Y.; Li, J.Q.

doi:10.1088/0029-5515/47/8/026

Cited by 14 publications

(12 citation statements)

References 37 publications

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“…It is interesting to note that in simulations, damping of the GAM due to coupling to higher m modes has been found [27,28,29]. It is evident that using the wave kinetic equation such damping would inevitably be found by allowing the energy to be distributed among several modes.…”

Section: Introductionmentioning

confidence: 96%

High frequency geodesic acoustic modes in electron scale turbulence

Anderson¹,

Skyman²,

Nordman³

et al. 2013

Nucl. Fusion

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In this work the finite β-effects of an electron branch of the geodesic acoustic mode (el-GAM) driven by electron temperature gradient (ETG) modes is presented. The work is based on a fluid description of the ETG mode retaining nonadiabatic ions and the dispersion relation for el-GAMs driven non-linearly by ETG modes is derived. The ETG growth rate from the fluid model is compared to the results found from gyrokinetic simulations with good agreement. A new saturation mechanism for ETG turbulence through the interaction with el-GAMs is found, resulting in a significantly enhanced ETG turbulence saturation level compared to the mixing length estimate. It is shown that the el-GAM may be stabilized by an increase in finite β as well as by increasing non-adiabaticity. The decreased GAM growth rates is due to the inclusion of the Maxwell stress.

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Section: Introductionmentioning

confidence: 96%

High frequency geodesic acoustic modes in electron scale turbulence

Anderson¹,

Skyman²,

Nordman³

et al. 2013

Nucl. Fusion

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“…A popular theory is that the zero magnetic shear at the radial location of the q min weakens the coupling of the poloidal harmonics, which creates a gap in the toroidal eigenmodes of the ion temperature gradient ͑ITG͒ instability 5 around the q min region due to the rarefaction of the mode rational surfaces 6 or the presence of a flow shear. 7 Beyond the linear theory, a gap in the fluctuation intensity could also be created by enhanced generation of sheared flows 6,8 and convective cells, 9 or the fluctuationinduced profile corrugations. 10 However, some nonlinear simulations do not observe such a mode gap due to the existence of a slablike branch of the ITG instability 11 or the turbulence spreading and avalanche.…”

Section: Introductionmentioning

confidence: 99%

Properties of microturbulence in toroidal plasmas with reversed magnetic shear

Deng

Zhang

2009

Physics of Plasmas

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Electrostatic drift wave turbulence in tokamak plasmas with reversed magnetic shear is studied using global gyrokinetic particle simulations. The linear eigenmode of the ion temperature gradient (ITG) instability exhibits a mode gap around the minimum safety factor (qmin) region, particularly when qmin is an integer, due to the rarefaction of rational surfaces. The collisionless trapped electron mode (CTEM) instability is suppressed in the negative-shear region due to the reversal of the toroidal precessional drift of trapped electrons. However, after nonlinear saturation, the ITG gap is filled up by the turbulence spreading and the CTEM fluctuation propagates into the stable negative-shear region. The steady state turbulence occupies the whole volume without any identifiable gap or coherent structures of the heat conductivity, perturbed temperature, or zonal flows in the qmin location or the reversed shear region. Our finding indicates that the electrostatic drift wave turbulence itself does not support either linear or nonlinear mechanism for the formation of internal transport barriers in the reversed magnetic shear when qmin crossing an integer.

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“…It is interesting to note that in simulations, damping of the GAM due to coupling to higher m modes has been found. [31,32,33] In a careful evaluation of the contributions from higher m modes it can be shown that they are, in general, of the order ǫ n smaller. However, the effect of higher harmonics is increased by the square of the safety factor (q) and thus in order to evaluate the effects a more detailed study is called for.…”

Section: Introductionmentioning

confidence: 99%

Effects of the Second Harmonic on the GAM in Electron Scale Turbulence

Anderson,

Nordman,

Singh

2014

Preprint

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The effects higher order harmonics have been self-consistently included in the derivation of the electron branch of the electron Geodesic Acoustic Mode (el-GAM) in an Electron-Temperature-Gradient (ETG) turbulence background. The work is based on a two-fluid model including finite β-effects while retaining non-adiabatic ions. In solving the linear dispersion relation, it is found that the due to the coupling to the m = 2 mode the real frequency may be significantly altered and yield higher values.

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Turbulence suppression in the neighbourhood of a minimum-qsurface due to zonal flow modification in reversed shear tokamaks

Cited by 14 publications

References 37 publications

High frequency geodesic acoustic modes in electron scale turbulence

High frequency geodesic acoustic modes in electron scale turbulence

Properties of microturbulence in toroidal plasmas with reversed magnetic shear

Effects of the Second Harmonic on the GAM in Electron Scale Turbulence

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