Simulating gyrokinetic microinstabilities in stellarator geometry with GS2

Baumgaertel, J. A.; Belli, E. A.; Dorland, W.; Guttenfelder, W.; Hammett, G. W.; Mikkelsen, D. R.; Rewoldt, G.; Tang, W. M.; Xanthopoulos, P.

doi:10.1063/1.3662064

Cited by 27 publications

(40 citation statements)

References 35 publications

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“…The simulations are fully electromagnetic (/; dA k ; dB k ), including a pitch angle scattering collision operator and three plasma species deuterium D, carbon C, and electrons e. In all calculations, the ballooning parameter h 0 34 is set to zero, the usual location of the maximum growth rates. 35 A few scans over the ballooning parameter were performed with no major increase in the growth rate values when compared to the values at h 0 ¼ 0. To insure sufficient numerical resolution, convergence tests (e.g., GS2 grid convergence tests including the extent of the poloidal angle h or the time step dt) were performed.…”

Section: Survey Of Modes Within the Pedestal Region Of Highly Shmentioning

confidence: 99%

Linear gyrokinetic simulations of microinstabilities within the pedestal region of H-mode NSTX discharges in a highly shaped geometry

et al. 2016

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This version is available at https://strathprints.strath.ac.uk/57449/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output.Linear gyrokinetic simulations of microinstabilities within the pedestal region of H-mode NSTX discharges in a highly shaped geometry Linear (local) gyrokinetic predictions of edge microinstabilities in highly shaped, lithiated and non-lithiated NSTX discharges are reported using the gyrokinetic code GS2. Microtearing modes dominate the non-lithiated pedestal top. The stabilization of these modes at the lithiated pedestal top enables the electron temperature pedestal to extend further inwards, as observed experimentally. Kinetic ballooning modes are found to be unstable mainly at the mid-pedestal of both types of discharges, with unstable trapped electron modes nearer the separatrix region. At electron wavelengths, electron temperature gradient (ETG) modes are found to be unstable from mid-pedestal outwards for g e; exp $ 2:2, with higher growth rates for the lithiated discharge. Near the separatrix, the critical temperature gradient for driving ETG modes is reduced in the presence of lithium, reflecting the reduction of the lithiated density gradients observed experimentally. A preliminary linear study in the edge of non-lithiated discharges shows that the equilibrium shaping alters the electrostatic modes stability, which was found more unstable at high plasma shaping. Published by AIP Publishing.

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Section: Survey Of Modes Within the Pedestal Region Of Highly Shmentioning

confidence: 99%

Linear gyrokinetic simulations of microinstabilities within the pedestal region of H-mode NSTX discharges in a highly shaped geometry

et al. 2016

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“…5. These simulations treat both the ions and the electrons kinetically, with the correct mass ratio, and the geometry is that of the high-mirror configuration of Wendelstein 7-X, with constant density, electron temperature T e = 8.2 keV, and an ion temperature profile given by The GENE and GS2 codes were both originally developed to operate in tokamak flux-tube geometry, but have later been extended to be able to treat stellarator flux tubes [64,66]. GS2 found the linear threshold for ITG modes with adiabatic electrons in NSCX to be a/L T i ≃ 1 − 2, where a is the minor radius and L T i the ion temperature gradient scale length, and electrostatic simulations with kinetic electrons also found density-gradient-driven TEMs, in agreement with earlier simulations using the FULL code [63].…”

Section: Gyrokinetic Simulationsmentioning

confidence: 99%

Stellarator and tokamak plasmas: a comparison

Helander

Beidler

Bird

et al. 2012

Plasma Phys. Control. Fusion

138

181

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An overview is given of physics differences between stellarators and tokamaks, including magnetohydrodynamic equilibrium, stability, fast-ion physics, plasma rotation, neoclassical and turbulent transport, and edge physics. Regarding microinstabilities, it is shown that the ordinary, collisionless trapped-electron mode is stable in large parts of parameter space in stellarators that have been designed so that the parallel adiabatic invariant decreases with radius. Also, the first global, electromagnetic, gyrokinetic stability calculations done for Wendelstein 7-X suggest that kinetic ballooning modes are more stable than in a typical tokamak.

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“…Instabilities including kinetic electrons have not been studied extensively in stellarators. Although there are some results focusing on W7-X 6,7 and NCSX [8][9][10] as well as comparisons of different stellarators 11 , these are not sufficient to explain why certain stellarators are more resilient against microinstabilities than others. In the present paper, two stellarators approaching quasi-isodynamicity, W7-X and QIPC, are compared with the DIII-D tokamak and the NCSX stellarator, which are both distinctly non-quasi-isodynamic.…”

Section: Introductionmentioning

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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Simulating gyrokinetic microinstabilities in stellarator geometry with GS2

Cited by 27 publications

References 35 publications

Linear gyrokinetic simulations of microinstabilities within the pedestal region of H-mode NSTX discharges in a highly shaped geometry

Linear gyrokinetic simulations of microinstabilities within the pedestal region of H-mode NSTX discharges in a highly shaped geometry

Stellarator and tokamak plasmas: a comparison

Collisionless microinstabilities in stellarators. II. Numerical simulations

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