## 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:

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

- Publication Date:

- Research Org.:
- Univ. of California, San Diego, CA (United States)

- Sponsoring Org.:
- USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)

- 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

### Citation Formats

```
Li, J. C., and Diamond, P. H. How shear increments affect the flow production branching ratio in CSDX. United States: N. p., 2018.
Web. doi:10.1063/1.5033911.
```

```
Li, J. C., & Diamond, P. H. How shear increments affect the flow production branching ratio in CSDX. United States. doi:10.1063/1.5033911.
```

```
Li, J. C., and Diamond, P. H. Thu .
"How shear increments affect the flow production branching ratio in CSDX". United States. doi:10.1063/1.5033911. https://www.osti.gov/servlets/purl/1540215.
```

```
@article{osti_1540215,
```

title = {How shear increments affect the flow production branching ratio in CSDX},

author = {Li, J. C. and Diamond, P. H.},

abstractNote = {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, PzR/PyR, 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., ΠxzRes) and turbulent viscosity (χzDW) by the same factor |<vy>'|-2Δx-2Ln-2ρs2cs2, where Δx is the distance relative to the reference point where <vy>=0 in the plasma frame. Therefore, the stationary state axial flow shear is not affected by azimuthal flow shear to leading order since <vz>'~ΠxzRes/χzDW.},

doi = {10.1063/1.5033911},

journal = {Physics of Plasmas},

number = 6,

volume = 25,

place = {United States},

year = {2018},

month = {6}

}

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