Inhomogeneous magnetic-field-aligned ion flow measured in a Q machine

Radial profiles of ion flow v(d)(r) are measured with laser-induced fluorescence for cases in which the flow direction is parallel (v(d)>0) and/or antiparallel (v(d)<0) to the equilibrium magnetic field. Experiments are conducted in the barium-ion plasma of a double-ended Q machine. In cases where the ionizers associated with the two ends are not biased relative to each other, two distinct, counterstreaming ion-beam populations are evident. The insertion of blocking electrodes introduces inhomogeneity into the density profiles of the ion populations without effecting the homogeneity of the radial profile of each population's drift velocity. In cases where the two ionizers are biased relative to each other, a single ion population exists. Variation in the radial profile of the ion population's parallel drift velocity v(d) is produced such that (dv(d)/dr) can be negative or positive with magnitudes 0-70% of the ion gyrofrequency omega(ci). These results are discussed in the context of beam-driven and velocity-shear-driven instabilities. Laboratory and space measurements of sheared parallel flow and counterstreaming ion beams are compared. (C) 2002 American Institute of Physics.