"Absolute Universal Instability" Is Not Universal

Tsang, K. T.; Catto, Peter J.; Whitson, J. C.; Smith, J.H.

doi:10.1103/physrevlett.40.327

Cited by 175 publications

(54 citation statements)

References 5 publications

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“…Thus, up to that point, the speculation was that the universal mode without or with weak shear is always unstable. However, in contradiction to all previous works, Ross and Mahajan 3 and Tsang et al 4 reported that the universal instability or collisionless drift instability in the presence of magnetic shear is always stable in the slab geometry, irrespective of the strength of the shear or transverse wave number when one takes into account the full electron dispersion function. The observed stability is attributed primarily to the stabilizing influence of the nonresonant electrons.…”

Section: Introductioncontrasting

confidence: 40%

Toroidal universal drift instability: A global gyrokinetic study

Chowdhury

Ganesh

Brunner³

et al. 2010

Physics of Plasmas

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An electron density gradient driven instability identified as the toroidal branch of the universal drift instability is studied using a global gyrokinetic model treating both electrons and ions fully nonadiabatically and valid at all orders in the ratio of the Larmor radius to the wavelength. The physics of the magnetic drift resonance, Landau resonance and transit resonance, which are considered to be important for the toroidal universal mode, are kept for both species. A systematic parametric study is carried out for the mode. The toroidal universal drift mode is observed to sustain finite temperature gradient and can thus coexist with the temperature gradient driven modes and may contribute to the observed particle transport along with other drift modes. Especially at intermediate scales between the ion temperature gradient driven mode and electron temperature gradient driven mode, this branch of the drift instability can also be a plausible candidate for the observed particle loss. The effect of magnetic fluctuations on the mode is also investigated. In contrast to the slab mode, the toroidal branch of the universal drift mode is found to be strongly stabilized by electromagnetic effects at finite plasma ␤. Finally, the effect of trapped electrons on the universal mode is studied and compared with the other possible modes in the same parameter regime, namely, ion temperature gradient mode in the presence of trapped electrons and pure trapped electron modes.

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Section: Introductioncontrasting

confidence: 40%

Toroidal universal drift instability: A global gyrokinetic study

Chowdhury

Ganesh

Brunner³

et al. 2010

Physics of Plasmas

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“…Stability is the opposite limit of small k y is expected since Refs. [1,2] are valid there. A region of stability also exists around k y ρ i ≈ 2 when a realistic mass ratio is used.…”

Section: Mode Propertiesmentioning

confidence: 99%

“…Notice the integral equation (4) from this gyrokinetic approach is manifestly different from the differential eigenmode equations in Refs. [1][2][3].…”

Section: Gyrokinetic Modelmentioning

confidence: 99%

“…Following a series of papers in 1978 [1][2][3], it has been widely accepted that drift waves in a plasma in a sheared magnetic field, in the absence of parallel current, temperature gradients, and magnetic curvature, are absolutely stable. In other words, the "universal mode" driven by the density gradient in slab geometry [4,5] becomes absolutely stable if any magnetic shear is included.…”

Section: Introductionmentioning

confidence: 99%

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Universal Instability for Wavelengths below the Ion Larmor Scale

2015

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We demonstrate that the universal mode driven by the density gradient in a plasma slab can be absolutely unstable even in the presence of reasonable magnetic shear. Previous studies from the 1970s that reached the opposite conclusion used an eigenmode equation limited to Lx ρi, where Lx is the scale length of the mode in the radial direction, and ρi is the ion Larmor radius. Here we instead use a gyrokinetic approach which does not have this same limitation. Instability is found for perpendicular wavenumbers ky in the range 0.7 kyρi 100, and for sufficiently weak magnetic shear: Ls/Ln 17, where Ls and Ln are the scale lengths of magnetic shear and density. Thus, the plasma drift wave in a sheared magnetic field may be unstable even with no temperature gradients, no trapped particles, and no magnetic curvature.

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“…Ten years later, two independent groups [5,6] came to the conclusion that the electron dynamics was not properly treated in [4] (the principal part of the plasma dispersion function was not included, an inheritance from [2]). With "outgoing waves" and the complete electron response, under no condition normal eigenmodes could be found in the sheared slab.…”

Section: Introductionmentioning

confidence: 99%

Finite system size effects on drift wave stability

Militello

Ottaviani²,

Wynn

2014

Physics of Plasmas

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Unstable electrostatic resistive modes, driven by density gradients, are identified in a bounded sheared slab. The boundary conditions play a crucial role and are shown to change the nature of the problem, which is related to so called "universal" mode. The dispersion relation and the structure of the eigenmodes of the instability are derived and are shown to depend on a limited set of dimensionless parameters. The occurrence and possible impact of these modes on numerical simulations and actual plasmas are discussed.

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"Absolute Universal Instability" Is Not Universal

Cited by 175 publications

References 5 publications

Toroidal universal drift instability: A global gyrokinetic study

Toroidal universal drift instability: A global gyrokinetic study

Universal Instability for Wavelengths below the Ion Larmor Scale

Finite system size effects on drift wave stability

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