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

Abstract

A gyrokinetic linear stability analysis of a collisionless slab geometry in the local approximation is introduced. 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 ρi~1 and vanish in the long wavelength k →0 limit. This report 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= $$\sqrt{β/[2(1+β)]C_{s}/|L_{p}|}$$ with C$$^{2}_{s}$$ =p 00 for k →0 and is universally unstable for 1/L p≠0. Here, we show that 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$$^{\prime}_{0}$$ 0 =0 inconsistent if p$$^{\prime}_{0}$$ ≠0.

Authors:
 [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Dartmouth College, Hanover, NH (United States)
Publication Date:
Research Org.:
Dartmouth College, Hanover, NH (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1540179
Alternate Identifier(s):
OSTI ID: 1437336
Grant/Contract Number:  
SC0010508; DOE-SC-0010508
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 25; Journal Issue: 5; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English

Citation Formats

Rogers, Barrett N., Zhu, Ben, and Francisquez, Manaure. Gyrokinetic theory of slab universal modes and the non-existence of the gradient drift coupling (GDC) instability. United States: N. p., 2018. Web. doi:10.1063/1.5024748.
Rogers, Barrett N., Zhu, Ben, & Francisquez, Manaure. Gyrokinetic theory of slab universal modes and the non-existence of the gradient drift coupling (GDC) instability. United States. doi:10.1063/1.5024748.
Rogers, Barrett N., Zhu, Ben, and Francisquez, Manaure. Wed . "Gyrokinetic theory of slab universal modes and the non-existence of the gradient drift coupling (GDC) instability". United States. doi:10.1063/1.5024748. https://www.osti.gov/servlets/purl/1540179.
@article{osti_1540179,
title = {Gyrokinetic theory of slab universal modes and the non-existence of the gradient drift coupling (GDC) instability},
author = {Rogers, Barrett N. and Zhu, Ben and Francisquez, Manaure},
abstractNote = {A gyrokinetic linear stability analysis of a collisionless slab geometry in the local approximation is introduced. 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⊥ρi~1 and vanish in the long wavelength k⊥→0 limit. This report 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= $\sqrt{β/[2(1+β)]C_{s}/|L_{p}|}$ with C$^{2}_{s}$ =p0/ρ0 for k⊥→0 and is universally unstable for 1/Lp≠0. Here, we show that the GDC instability is a spurious, unphysical artifact that erroneously arises due to the failure to respect the total equilibrium pressure balance p0+B$^{2}_{0}$ /(8π)=constant, which renders the assumption B$^{\prime}_{0}$ 0 =0 inconsistent if p$^{\prime}_{0}$ ≠0.},
doi = {10.1063/1.5024748},
journal = {Physics of Plasmas},
number = 5,
volume = 25,
place = {United States},
year = {2018},
month = {5}
}

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