Universal Instability for Wavelengths below the Ion Larmor Scale

Landreman, Matt; Antonsen, Thomas M.; Dorland, W.

doi:10.1103/physrevlett.114.095003

Cited by 30 publications

(42 citation statements)

References 20 publications

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“…δA ). Moreover, the stability of the slab has been re-examined at the sub-ion Larmor scale and found to be unstable even in the presence of shear 24 due to a relaxation of the assumption that the radial extent (in the direction of the density gradient) of the mode is much larger than the ion Larmor radius (ρ i ). This has reinvigorated the exploration of universal modes, with Ref.…”

Section: Introductionmentioning

confidence: 99%

Gyrokinetic theory of slab universal modes and the non-existence of the gradient drift coupling (GDC) instability

2018

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A gyrokinetic linear stability analysis of a collisionless slab geometry in the local approximation is presented. We focus on k = 0 universal (or entropy) modes driven by plasma gradients at small and large plasma β. These are small scale non-MHD instabilities with growth rates that typically peak near k ⊥ ρ i ∼ 1 and vanish in the long wavelength k ⊥ → 0 limit. This work also discusses a mode known as the Gradient Drift Coupling (GDC) instability previously reported in the gyrokinetic literature, which has a finite growth rate γ = β/[2(1 + β)]C s /|L p | with C 2 s = p 0 /ρ 0 for k ⊥ → 0 and is universally unstable for 1/L p = 0. We show the GDC instability is a spurious, unphysical artifact that erroneously arises due to the failure to respect the total equilibrium pressure balance p 0 + B 2 0 /(8π) = constant, which renders the assumption B 0 = 0 inconsistent if p 0 = 0. a)

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Section: Introductionmentioning

confidence: 99%

Gyrokinetic theory of slab universal modes and the non-existence of the gradient drift coupling (GDC) instability

2018

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“…We have chosen this simple instability for this first study of the effects produced by trajectory trapping or eddying in order to avoid interferences with other processes. The stabilizing effect produced by a sheared magnetic field on bound eigenmodes [44], or, alternatively, the instability for wavelengths below the ion Larmor scale [45] are not considered here. The effects of the magnetic shear on transport were studied using DTM in [46], which enables the extension of the present study to more complex confining configuration.…”

Section: Test Modesmentioning

confidence: 99%

Random and quasi-coherent aspects in particle motion and their effects on transport and turbulence evolution

Vlad

Spineanu

2017

New J. Phys.

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The quasi-coherent effects in two-dimensional incompressible turbulence are analyzed starting from the test particle trajectories. They can acquire coherent aspects when the stochastic potential has slow time variation and the motion is not strongly perturbed. The trajectories are, in these conditions, random sequences of large jumps and trapping or eddying events. Trapping determines quasicoherent trajectory structures, which have a micro-confinement effect that is reflected in the transport coefficients. They determine non-Gaussian statistics and flows associated to an average velocity. Trajectory structures also influence the test modes on turbulent plasmas. Nonlinear damping and generation of zonal flow modes is found in drift turbulence in uniform magnetic field. The coupling of test particle and test mode studies permitted to evaluate the self-consistent evolution of the drift turbulence in an iterated approach. The results show an important nonlinear effect of ion diffusion, which can prevent the transition to the nonlinear regime at small drive of the instability. At larger drive, quasi-coherent trajectory structures appear and they have complex effects on turbulence.eddying. The general conclusion of these studies is that trajectory trapping or eddying determines non-standard statistics of trajectories: non-Gaussian distributions, long time Lagrangian correlations (memory), strongly modified transport coefficients and an increased degree of coherence. The trapped trajectories form quasicoherent structures similar to fluid vortices.Very recent results [15] have shown that these methods could be the basis for the development of a theoretical approach for the study of test modes in turbulent plasmas. It is similar to the Lagrangian approach initiated by Dupree [16,17] and developed in the 1970s. The assumption of random trajectories with Gaussian distribution limited the application of Dupree's method to the quasilinear regime. The DTM and NSA enable the evaluation of the average propagator of the test modes in the nonlinear regime and extend the theoretical procedure to the complex processes that are generated in these conditions. The tendency of drift turbulence evolution beyond the quasilinear regime was obtained in [15].We present a theoretical approach to the study of turbulence evolution, the iterated self-consistent method (ISC). It is based on the analysis of the test particles and test modes in turbulent plasmas. Both test particle and test mode studies start from given statistical description of the turbulence. However, the coupling of these problems can lead to the evaluation of turbulence evolution and to the understanding of the nonlinear processes that are generated. The ISC is applied here to the drift turbulence in plasmas confined in uniform magnetic fields.The paper is organized as follows. The physical processes analyzed in this paper and the main ideas that are followed in this study are presented in section 2. Section 3 contains the test particle studies of transport, the DTM and the NS...

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“…However, the inherent non-modal character of density gradient driven DWs (cf. [19,[21][22][23]) allows for transient amplification to sustain DW turbulence [24][25][26][27].…”

Section: Introductionmentioning

confidence: 99%

“…After nearly 60 years density gradient driven DW instabilities remain an active theoretical research field. The latest efforts focus on a unified description of the collisional and collisionless DW instability [28,29] or proof instability for collisionless DWs in sheared magnetic fields after decades of misconception [19].…”

Section: Introductionmentioning

confidence: 99%

The collisional drift wave instability in steep density gradient regimes

2019

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The collisional drift wave instability in a straight magnetic field configuration is studied within a full-F gyro-fluid model, which relaxes the Oberbeck-Boussinesq (OB) approximation. Accordingly, we focus our study on steep background density gradients. In this regime we report on corrections by factors of order one to the eigenvalue analysis of former OB approximated approaches as well as on spatially localised eigenfunctions, that contrast strongly with their OB approximated equivalent. Remarkably, non-modal phenomena arise for large density inhomogeneities and for all collisionalities. As a result, we find initial decay and non-modal growth of the free energy and radially localised and sheared growth patterns. The latter non-modal effect sustains even in the nonlinear regime in the form of radially localised turbulence or zonal flow amplitudes. II. GYRO-FLUID MODELOur analysis is based on an energetically consistent full-F gyro-fluid model [39], which is derived by taking the gyro-fluid moments over the gyro-kinetic Vlasov-Maxwell equations [40]. In order to ease the following

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Universal Instability for Wavelengths below the Ion Larmor Scale

Cited by 30 publications

References 20 publications

Gyrokinetic theory of slab universal modes and the non-existence of the gradient drift coupling (GDC) instability

Gyrokinetic theory of slab universal modes and the non-existence of the gradient drift coupling (GDC) instability

Random and quasi-coherent aspects in particle motion and their effects on transport and turbulence evolution

The collisional drift wave instability in steep density gradient regimes

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