Observation of Turbulent-Driven Shear Flow in a Cylindrical Laboratory Plasma Device

An azimuthally symmetric radially sheared plasma fluid flow is observed to spontaneously form in a cylindrical magnetized helicon plasma device with no external sources of momentum input. A turbulent momentum conservation analysis shows that this shear flow is sustained by the Reynolds stress generated by collisional drift turbulence in the device. The results provide direct experimental support for the basic theoretical picture of drift-wave–shear-flow interactions.

Figure 1

(a) Time-averaged density profile, (b) frequency spectra of density (black), and azimuthal velocity (red) fluctuations, at $r=3\mathrm{cm}$ (solid curves) and $r=5\mathrm{cm}$ (dashed curves). (c) Time-averaged radial particle flux profile, and (d) rms amplitudes of density fluctuations (solid black line), radial velocity fluctuations (solid blue line), and azimuthal velocity fluctuations (solid red line) filtered between 5–50 kHz, as well as azimuthal velocity fluctuations between 0–5 kHz (dashed yellow).

Figure 2

(a) Radial profile of turbulent Reynolds stress $⟨{\tilde{V}}_r{\tilde{V}}_{\theta }⟩$. (b) Radial profile of ion viscosity used in momentum balance.

Figure 3

Mean azimuthal velocity profile predicted by force balance (solid line), and measured via time-delay estimation (diamonds).