d.c. electric field stabilization of plasma fluctuations due to a velocity shear in the parallel ion flow

Consideration is given to the suggestion by Basu and Coppi (1988, 1989) that the DE-2 observations of broadband turbulence associated with sheared ion flows can be explained by electrostatic waves driven by a sheared ion flow along the magnetic field. It is pointed out that such a theory ignores the stronger shear in the ion flow transverse to the magnetic field, and that, when this shear is taken into account, the modes described by Basu and Coppi are easily destabilized. The theory of Basu and Coppi is shown to break down even when the shear in the parallel flow exceeds the shear in the transverse flow.