Investigation of ion drift waves in the PSI-2 using Langmuir-probes

The properties of ion drift waves observed in the rotating magnetized plasm a column of the PSI-2 are analysed. Their parallel wave numbers are found t o be nearly zero, the measured azimuthal dispersion relation is approximate ly linear, and the azimuthal phase velocity is nearly equal to the azimutha l ion drift velocity. Furthermore, the potential fluctuations always lag be hind the density fluctuations with a phase shift slightly below pi. A simple analytical model, describing the potential- and density distributi on of the ion drift wave, shows the underlying mechanism of the ion drift i nstability. Finally, a classification of the observed ion drift instability is given.