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Abstract. Recent sounding rocket experiments, such as SCIFER, AMICIST, and ARCS-4, and satellite data from FAST, Freja, DE-2, and HILAT, provide compelling evidence of a correlation between small-scale spatial plasma inhomogeneities, broadband low-frequency waves, and transversely heated ions. These naturally arising, localized inhomogeneities can lead to sheared cross-magnetic-field plasma flows, a situation that has been shown to have potential for instability growth. Experiments performed in the Naval Research Laboratory's Space Physics Simulation Chamber demonstrate that broadband waves in the ion-cyclotron frequency range can be driven solely by a transverse, localized electric field, without the dissipation of a field-Migned current. Significant perpendicular ion energization resulting from these waves has been measured. Detailed comparisons with both theoretical predictions and space observations of electrostatic waves found in the presence of sheared cross-magnetic-field plasma flow are made.

A small spherical probe is used in conjunction with a network analyzer to determine the impedance of the probe-plasma system over a wide frequency range. Impedance curves are in good agreement with accepted circuit models with plasma-sheath and electron plasma frequency resonances easily identifiable. Clear transitions between capacitive and inductive modes as predicted by the model are identified. Sheath thickness and absolute electron density are determined from the location of these transitions. The absolute electron density indicated by the location of the impedance resonance is compared to measurements using the plasma oscillation method.

Abstract. Sheared flows in near-Earth space plasmas, both magnetic-field-aligned and cross-field, contribute to a rich array of phenomena which can be simulated in the laboratory. This has led to improved knowledge of the basic processes involving velocity shear operative in space, where it is not possible to conduct detailed and repeatable experiments with control over background parameters. Depending upon the flow characteristics, shear can contribute to either growth or damping of various plasma modes or, if sufficiently strong, can itself drive instabilities. These instabilities can have significant consequences in redefining the plasma equilibrium and can lead to energization and transport. A number of laboratory experiments have been performed to investigate the detailed physics associated with inhomogeneous space plasma flows. In this work, a review of in situ observations of processes associated with sheared flows and details of complementary laboratory experimental investigations is presented.

A category of oscillation identified with the inhomogeneous energy-density driven instability has been experimentally verified. This mode exploits the free energy available from shear in the Ex B Aow velocity. This shear is produced experimentally by applying different voltages to a segmented disk electrode located on axis at the end of a Q machine plasma column. As plasma conditions are varied between the two parameter regimes that, according to theory, correspond to the current-driven and shear-driven waves, the expected transition in mode characteristics is observed.PACS numbers: 52.35. Fp, 52.35.Qz, 94.20.Bb, 94.30.6m In this Letter we experimentally verify the existence of a new branch of plasma oscillation driven by velocity shear. Ganguli, Lee, and Palmadesso [1,2] predicted the