Observation of strong oscillations in an expanding plasma

Summary form only given, as follows. Strong oscillations (f/sub peak/ equivalent to 200 kHz) of plasma potential ( Delta Phi /kT/sub e/ approximately=2-4) and density ( Delta n/n approximately=0.2-0.5) have been observed in a two-electron-population plasma (f/sub pi/ approximately=1 MHz) which is expanding into vacuum along an external magnetic field (B approximately=0-50 G). During the expansion, ions are accelerated to very high energies (M/sub i/ nu /sup 2//2>or approximately=110 eV). The oscillations, which vanish in the absence of the magnetic field, increase in amplitude and frequency with an increase in the magnetic field and saturate at B approximately=35 G. Preliminary observations indicate that the oscillations exist only in the presence of a cross-field electric field that develops self-consistently. The magnitude (0-2 V/cm) and direction of the electric field are sensitive functions of background neutral pressure and the magnetic field. A two-probe correlations measurement has been performed to determine the wave number of the dominant mode in the observed oscillations. Initial results indicate that the correlation lengths are very long (l>10 cm) along the magnetic field and relatively short (l approximately=1 cm) in the azimuthal direction.<>