Observation of high-frequency ion instabilities in a cross-field plasma

This paper reports on the examination of the high-frequency ion dynamics in a low-pressure cross-field plasma. Measurements of the time-varying ion velocity distribution function were carried out by photon-counting laser-induced fluorescence spectroscopy. A temporal correlation was found between the low-frequency ionization process and the high frequency ion instability. The high-frequency spectral properties of the ion mean velocity are compared with a perturbed fluid model of the plasma flow on the source axis. The wavelength of the high-frequency mode is similar to the electric field extent outside the cavity. Surprisingly the mode appears only in the area of negative magnetic field gradient.