Observation of strong oscillations in an expanding plasma

The authors describe strong oscillations of plasma potential and density observed in a two-electron-population plasma which is expanding into vacuum along an external magnetic field. During the expansion, ions are accelerated to very high energies. Preliminary observations indicate that the oscillations exists only in the presence of a cross-field electric field which self-consistently develops. The magnitude and direction of the electric field is a sensitive function of background neutral pressure and the magnetic field. A two-probe correlation measurement was performed to determine the wavenumber of the dominant mode in the observed oscillations. Initial results are reported