Title: The ecology of flows and drift wave turbulence in CSDX: A model

Abstract

This paper describes the ecology of drift wave turbulence and mean flows in the coupled drift-ion acoustic wave plasma of a CSDX linear device. A 1D reduced model that studies the spatiotemporal evolution of plasma mean density $$\bar{n}$$, and mean flows $$\bar{v}$$y and $$\bar{v}$$z, in addition to fluctuation intensity ε, is presented. Here, $\epsilon =\langle {\tilde{n}}^2+{\left({\nabla }_{\perp }\tilde{\Phi }\right)}^2+{\tilde{v}}_z^2\rangle$ is the conserved energy field. The model uses a mixing length l_mix inversely proportional to both axial and azimuthal flow shear. This form of l_mix closes the loop on total energy. The model self-consistently describes variations in plasma profiles, including mean flows and turbulent stresses. It investigates the energy exchange between the fluctuation intensity and mean profiles via particle flux $\langle \tilde{n}{\tilde{v}}_x\rangle$ and Reynolds stresses $\langle {\tilde{v}}_x{\tilde{v}}_y\rangle$ and $\langle {\tilde{v}}_x{\tilde{v}}_z\rangle$ Acoustic coupling breaks parallel symmetry and generates a parallel residual stress Π res xz . The model uses a set of equations to explain the acceleration of $$\bar{v}_y$$ and $$\bar{v}_z$$ via ${\Pi }_{xy}^{res}\propto \nabla \stackrel{-}{n}$ and ${\Pi }_{xy}^{res}\propto \nabla \stackrel{-}{n}$. Flow dynamics in the parallel direction are related to those in the perpendicular direction through an empirical coupling constant σVT. This constant measures the degree of symmetry breaking in the 〈$$k_mk_z$$〉 correlator and determines the efficiency of ∇$$\bar{n}$$ in driving $$\bar{v}_z$$. The model also establishes a relation between ∇$$\bar{v}_y$$ and ∇$$\bar{v}_z$$, via the ratio of the stresses Π res xy and Π res xz . When parallel to perpendicular flow coupling is weak, axial Reynolds power $P_{xz}^{Re}=-\langle {\tilde{v}}_x{\tilde{v}}_z\rangle \nabla {\stackrel{-}{v}}_z$ is less than the azimuthal Reynolds power $P_{xy}^{Re}=-\langle {\tilde{v}}_x{\tilde{v}}_y\rangle \nabla {\stackrel{-}{v}}_y$∇$$\bar{v}_y$$. The model is then reduced to a 2-field predator/prey model where $$\bar{v}_z$$ is parasitic to the system and fluctuations evolve self-consistently. Finally, turbulent diffusion in CSDX follows the scaling: $D_{\text{CSDX}}=D_B{\rho }_{*}^{0.6}$, where D_B is the Bohm diffusion coefficient and ρ_* is the ion gyroradius normalized to the density gradient $|\nabla \stackrel{-}{n}/\stackrel{-}{n}|{}^{-1}$

Authors:

Hajjar, R. J. ^[1]; Diamond, P. H. ^[2]; Tynan, G. R. ^[3]

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+ Show Author Affiliations

1. Univ. of California, San Diego, CA (United States). Center for Energy Research
2. Univ. of California, San Diego, CA (United States). Center for Energy Research, Center for Astrophysics and Space Sciences; Center for Fusion Sciences, Southwestern Inst. of Physics, Chengdu, Sichuan (China)
3. Univ. of California, San Diego, CA (United States). Center for Energy Research; Center for Fusion Sciences, Southwestern Inst. of Physics, Chengdu, Sichuan (China)

Publication Date:

2018-02-01

Research Org.:

Univ. of California, San Diego, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Fusion Energy Sciences (FES)

OSTI Identifier:

1524572

Alternate Identifier(s):

OSTI ID: 1420214

Grant/Contract Number:  

FG02-04ER54738

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 25; Journal Issue: 2; 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