Title: Analytical and numerical study of the transverse Kelvin–Helmholtz instability in tokamak edge plasmas

Abstract

Sheared flows perpendicular to the magnetic field can be driven by the Reynolds stress or ion pressure gradient effects and can potentially influence the stability and turbulent saturation level of edge plasma modes. On the other hand, such flows are subject to the transverse Kelvin–Helmholtz (KH) instability. Here, the linear theory of KH instabilities is first addressed with an analytic model in the asymptotic limit of long wavelengths compared with the flow scale length. The analytic model treats sheared $$\boldsymbol{E}\times \boldsymbol{B}$$ flows, ion diamagnetism (including gyro-viscous terms), density gradients and parallel currents in a slab geometry, enabling a unified summary that encompasses and extends previous results. In particular, while ion diamagnetism, density gradients and parallel currents each individually reduce KH growth rates, the combined effect of density and ion pressure gradients is more complicated and partially counteracting. Secondly, the important role of realistic toroidal geometry is explored numerically using an invariant scaling analysis together with the 2DX eigenvalue code to examine KH modes in both closed and open field line regions. For a typical spherical torus magnetic geometry, it is found that KH modes are more unstable at, and just outside of, the separatrix as a result of the distribution of magnetic shear. Finally implications for reduced edge turbulence modelling codes are discussed.

Authors:

Myra, J. R. ^[1]; D’Ippolito, D. A. ^[1]; Russell, D. A. ^[1]; Umansky, M. V. ^[2]; Baver, D. A. ^[1]

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+ Show Author Affiliations

1. Lodestar Research Corporation, Boulder, CO (United States)
2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Publication Date:

Mon Apr 11 00:00:00 EDT 2016

Research Org.:

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Lodestar Research Corp., Boulder, CO (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Contributing Org.:

Lodestar Research Corporation Lawrence Livermore National Lab.

OSTI Identifier:

1463839

Alternate Identifier(s):

OSTI ID: 1248339

Report Number(s):

LLNL-JRNL-737835; LRC-16-164
Journal ID: ISSN 0022-3778; applab; 890878; TRN: US1902332

Grant/Contract Number:  

AC52-07NA27344; FG02-97ER54392

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Plasma Physics

Additional Journal Information:

Journal Volume: 82; Journal Issue: 02; Journal ID: ISSN 0022-3778

Publisher:

Cambridge University Press

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; plasma instabilities; Kelvin-Helmholtz; spherical torus