Study of strong cross-field sheared flow with the vorticity probe in the Large Plasma Device

This work reports evidence for the existence of coherent structures in steady-state shear-flow driven plasmas in the Large Plasma Device W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 1991 facility at UCLA. The measurements are performed with the vorticity probe VP , a probe that directly measures the plasma vorticity associated with the E B shear flow by means of a method that is both simpler and more accurate than the methods used in neutral fluids. Because the rate of change of vorticity is a key quantity in nonlinear models, as in the Hasegawa-Mima equation, its direct measurement is critical for verification purposes. The physical origin of the rate of change of plasma vorticity from E B flow is the divergence of the ion polarization current. Vortex coherent structures occur when the vorticity is a nonlinear function of the stream function. Statistical properties of vorticity are reported and shown to be consistent with the types of coherent structures created by the Kelvin-Helmholtz instability. Comparisons of the measured vortex characteristics with the results from nonlinear simulations of the systems is described. © 2006 American Institute of Physics. DOI: 10.1063/1.2179423