We report the development of a new diagnostic capable of measuring plasma ion distributions as a function of all three velocity-space coordinates. The diagnostic makes use of laser-induced fluorescence (LIF) and computer-assisted image reconstruction techniques. LIF yields highresolution, non perturbing measurements of one-dimensional distributions that are integrated in two directions through three-dimensional velocity space. Computer tomography allows for the unambiguous determination of the complete ion velocity distribution. In addition to a description of the diagnostic, examples of recovered distributions obtained from experiments are given, and the effects of the major steps in the data processing are discussed.

Laboratory experiments are presented simulating aspects of perpendicular ion heating and conic formation that are observed or hypothesized to occur in the terrestrial ionosphere and magnetosphere. Previous laboratory observations of ion conics in the presence of the current-driven electrostatic ion cyclotron wave are reviewed. Field-aligned ion beams, accompanied by beam-generated electrostatic ion cyclotron modes, resulted in perpendicular energization of beam ions and also the heating of background plasma ions. Antenna-launched broadband and narrow-band lower hybrid waves produced considerable perpendicular ion heating and non-Maxwellian "tail" formation. Laboratory results are discussed in light of in situ measurements by the S3-3 satellite and the MARIE sounding rocket.

Laboratory experiments have examined particular elements of proposed mechanisms for ion conic formation seen in the Earth's auroral-zone magnetosphere.A laser-induced fluorescence diagnostic measured the ion distribution function at many angles in velocity space, allotting tomographic techniques to reconstruct the multidimensional ion distribution function. Ion conies, as well as drifting Maxwellians, were observed.

The electrostatic ion-cyclotron instability can be excited in a single-ended Q-machine by a positively biased collector. According to infinite plasma theory the instability is triggered by the drifting electrons. Recently this explanation has been questioned since experiments by another group have shown that the excitation takes place solely near the collector. The excitation has been ascribed :o the collector sheath which has strong axial and radial gradients. In the present experiment we try to prove that drifting electrons are able to excite the ion-cyclotron instability. We produce an electron drift without the formation of a localized two-dimensional sheath. To that end the plasma electrons are delivered by a source which is spatially separated from the ion source. If the central section of these electrons is slightly accelerated by a grid we observe the instability.

An experiment in a single-ended Q-machine was conducted in which a voltage was applied between t h o concentric floating electrodes which terminated the plasma column. When the inner electrode was more than 200 V positive with respect to the outer one the electrostatic ion-qclotron instability was observed. In the usual case the electron current is drawn between the grounded (plasma generating) hot plate and a positively biased electrode, with only a small voltage needed to trigger the instability. However, the current threshold is the same for both cases. indicating that it is a critical electron drift speed, not a sheath effect, which is necessary for the instability.IT IS well known that electrostatic ion-cyclotron (EIC) waves can be destabilized in a magnetized plasma (MOTLEY and D'ASGELO. 1963). The EIC instability is excited by a driit of the plasma electrons through the ions. Since. in terms of the electron drift velocity. it has a very IOW threshold (DRLMMOND and ROSEN-BLLTH. 1962). the EIC instability has been observed in the solar plasma (HINATA, 1980). the magnetosphere (LYSAK et al.. 1980) and in laboratory plasmas. especially single-ended Q-machines (e.g.