Exceptional points in linear gyrokinetics

Kammerer, Matthias; Merz, F.; Jenko, F.

doi:10.1063/1.2909618

Cited by 53 publications

(43 citation statements)

References 21 publications

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“…[8][9][10][11] The results of this study are also expected to provide insights into the nonlinear effect of turbulence which is driven by the unstable linear eigenmodes studied here. Microturbulence and the associated transport in fusion plasmas frequently retain signatures of the underlying linear eigenmode spectra.…”

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confidence: 98%

Aspects of linear Landau damping in discretized systems

et al. 2013

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Discrete kinetic eigenmode spectra of electron plasma oscillations in weakly collisional plasma: A numerical study Phys. Plasmas 20, 012125 (2013) Non-planar ion-acoustic solitary waves and their head-on collision in a plasma with nonthermal electrons and warm adiabatic ions Phys. Plasmas 20, 012122 (2013) The incomplete plasma dispersion function: Properties and application to waves in bounded plasmas Phys. Plasmas 20, 012118 (2013) Effect of ion temperature on ion-acoustic solitary waves in a magnetized plasma in presence of superthermal electrons Phys. Plasmas 20, 012306 (2013) Additional information on Phys. Plasmas Basic linear eigenmode spectra for electrostatic Langmuir waves and drift-kinetic slab ion temperature gradient modes are examined in a series of scenarios. Collisions are modeled via a Lenard-Bernstein collision operator which fundamentally alters the linear spectrum even for infinitesimal collisionality [Ng et al., Phys. Rev. Lett. 83, 1974(1999. A comparison between different discretization schemes reveals that a Hermite representation is superior for accurately resolving the spectra compared to a finite differences scheme using an equidistant velocity grid. Additionally, it is shown analytically that any even power of velocity space hyperdiffusion also produces a Case-Van Kampen spectrum which, in the limit of zero hyperdiffusivity, matches the collisionless Landau solutions. V C 2013 American Institute of Physics. [http://dx

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confidence: 98%

Aspects of linear Landau damping in discretized systems

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“…in Ref. 31 ), even though propagation in the electron diamagnetic direction is more common 13,[32][33][34] . The energy analysis at gradients of a/L Te = 1.0 and a/L n = 0.5 (this time a slightly different wave number of k y ρ s = 1.1 was selected) reveals that the modes observed here are indeed electron-driven and thus ordinary TEMs.…”

Section: Trapped-electron Modes (Tem)mentioning

confidence: 99%

Collisionless microinstabilities in stellarators. II. Numerical simulations

2013

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Microinstabilities exhibit a rich variety of behavior in stellarators due to the many degrees of freedom in the magnetic geometry. It has recently been found that certain stellarators (quasi-isodynamic ones with maximum-J geometry) are partly resilient to trapped-particle instabilities, because fast-bouncing particles tend to extract energy from these modes near marginal stability. In reality, stellarators are never perfectly quasi-isodynamic, and the question thus arises whether they still benefit from enhanced stability. Here the stability properties of Wendelstein 7-X and a more quasi-isodynamic configuration, QIPC, are investigated numerically and compared with the National Compact Stellarator Experiment (NCSX) and the DIII-D tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, ion-temperature-gradient modes, trapped-electron modes and mixed-type instabilities are studied. Wendelstein 7-X and QIPC exhibit significantly reduced growth rates for all simulations that include kinetic electrons, and the latter are indeed found to be stabilizing in the energy budget. These results suggest that imperfectly optimized stellarators can retain most of the stabilizing properties predicted for perfect maximum-J configurations.

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“…Furthermore, subdominant instabilities are tracked employing the eigenvalue solver integrated into GENE, [49][50][51] which allows a more complete comparison between linear and nonlinear transport characteristics. For the present linear simulations, we employ a resolution of 31 × 64 × 64 × 16 in (k x , z, v , µ) dimensions, analyzing a single k y mode at a time.…”

Section: B Microinstability Investigationsmentioning

confidence: 99%

Characterizing turbulent transport in ASDEX Upgrade L-mode plasmas via nonlinear gyrokinetic simulations

et al. 2013

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The nature and level of turbulent transport in the outer core of low-confinement (L-mode) discharges performed at the ASDEX Upgrade tokamak [A. Kallenbach et al., Nucl. Fusion 51, 094012 (2011)] are examined. Previously, it was found that for an L-mode discharge of the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] gyrokinetic simulations were unable to reproduce the experimental ion heat flux, underestimating it by almost an order of magnitude. In the present work, employing the GENE gyrokinetic turbulence code, an extensive nonlinear study is performed for L-mode discharges of ASDEX Upgrade in order to cross-check this observation. It is shown that no systematic underprediction can be found in these simulations-instead, discrepancies with respect to experimental transport levels are small enough to be resolved within the uncertainties of the experimental profiles. Moreover, it is shown that some turbulence properties resemble closely those of the underlying linear microinstabilities at least out to 90% of the minor radius, so that quasilinear transport models remain in principle applicable even for these parameters, provided that appropriate nonlinear saturation rules can be developed.

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Exceptional points in linear gyrokinetics

Cited by 53 publications

References 21 publications

Aspects of linear Landau damping in discretized systems

Aspects of linear Landau damping in discretized systems

Collisionless microinstabilities in stellarators. II. Numerical simulations

Characterizing turbulent transport in ASDEX Upgrade L-mode plasmas via nonlinear gyrokinetic simulations

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