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$$^{2}_{s}$$ =p₀/ρ₀ 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 p₀+B$$^{2}_{0}$$ /(8π)=constant, which renders the assumption B$$^{\prime}_{0}$$ 0 =0 inconsistent if p$$^{\prime}_{0}$$ ≠0.

Authors:

Rogers, Barrett N. ^[1]; Zhu, Ben  ^[1];

• Search DOE PAGES for author "Zhu, Ben"
• Search DOE PAGES for ORCID "0000-0003-2225-045X"

Francisquez, Manaure  ^[1]

• Search DOE PAGES for author "Francisquez, Manaure"
• Search DOE PAGES for ORCID "0000-0002-8247-3770"

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+ Show Author Affiliations

1. Dartmouth College, Hanover, NH (United States)

Publication Date:

Wed May 16 00:00:00 EDT 2018

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

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY