Test-particle measurements of plasma cross-field ion transport show a
dramatic change associated with the presence of sheared plasma flow pa
rallel to a fixed magnetic field. Experimental conditions for enhanced
transport are consistent with a simple model of shear flow instabilit
y. Observed modulations in the tagging transfer function suggest a non
linear model for the ion dynamics, and a spatially varying shift in th
e ion gyrofrequency. The problem of determining electric fields from t
est-particle measurements is posed.