Title: How shear increments affect the flow production branching ratio in CSDX

Abstract

In this study, the coupling of turbulence-driven azimuthal and axial flows in a linear device absent magnetic shear (Controlled Shear Decorrelation Experiment) is investigated. In particular, we examine the apportionment of Reynolds power between azimuthal and axial flows, and how the azimuthal flow shear affects axial flow generation and saturation by drift wave turbulence. We study the response of the energy branching ratio, i.e., ratio of axial and azimuthal Reynolds powers, $P_z^R/P_y^R$, to incremental changes of azimuthal and axial flow shears. We show that increasing azimuthal flow shear decreases the energy branching ratio. When axial flow shear increases, this ratio first increases but then decreases to zero. The axial flow shear saturates below the threshold for parallel shear flow instability. The effects of azimuthal flow shear on the generation and saturation of intrinsic axial flows are analyzed. Azimuthal flow shear slows down the modulational growth of the seed axial flow shear, and thus reduces intrinsic axial flow production. Azimuthal flow shear reduces both the residual Reynolds stress (of axial flow, i.e., ${\Pi }_{xz}^{Res}$) and turbulent viscosity ( ${\chi }_z^{DW}$) by the same factor $|<v_y>\text{'}{|}^{-2}{\Delta }_x^{-2}{L}_n^{-2}{\rho }_s^2{c}_s^2$, where Δ_x is the distance relative to the reference point where $<v_y>=0$ in the plasma frame. Therefore, the stationary state axial flow shear is not affected by azimuthal flow shear to leading order since $<v_z>\text{'}~{\Pi }_{xz}^{Res}/{\chi }_z^{DW}$.

Authors:

Li, J. C.  ^[1];

• Search DOE PAGES for author "Li, J. C."
• Search DOE PAGES for ORCID "0000-0002-8230-2226"

Diamond, P. H. ^[1]

---

+ Show Author Affiliations

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

Publication Date:

Thu Jun 07 00:00:00 EDT 2018

Research Org.:

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

Sponsoring Org.:

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

OSTI Identifier:

1540215

Alternate Identifier(s):

OSTI ID: 1441049

Grant/Contract Number:  

FG02-04ER54738

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 25; Journal Issue: 6; 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