How shear increments affect the flow production branching ratio in CSDX

Journal Article · Thu Jun 07 00:00:00 EDT 2018 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.5033911· OSTI ID:1540215

Li, J. C.  ^[1]; Diamond, P. H. ^[1]

---

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

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 $<v_z>\text{'}~{\Pi }_{xz}^{Res}/{\chi }_z^{DW}$.

• Research Organization: Univ. of California, San Diego, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• Grant/Contract Number: FG02-04ER54738
• OSTI ID: 1540215
• Alternate ID(s): OSTI ID: 1441049
• Journal Information: Physics of Plasmas, Vol. 25, Issue 6; ISSN 1070-664X
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY