INTERFERENCE PATTERNS IN THE SPACELAB-2 PLASMA-WAVE DATA - LOWER-HYBRID WAVES DRIVEN BY PICKUP IONS

During the Spacelab 2 mission the University of Iowa's Plasma Diagnost ics Package (PDP) was released from the shuttle to explore the plasma environment around the shuttle. Wideband spectrograms were obtained fr om the PDP at frequencies from 0 to 30 kHz and distances up to 400 m f rom the shuttle. The wideband data frequently showed antenna interfere nce patterns when the PDP was on the downstream side of the shuttle. A nalysis of these interference patterns allows a determination of the w avelength, the plasma rest frame frequency, the direction of propagati on, the power spectrum, and in some cases the location of the source. We concentrate our analysis on interference patterns due to lower hybr id waves: waves which have rest frame frequencies near the lower hybri d frequency and propagate perpendicular to the magnetic field. The wav es have an almost flat dispersion relation with frequencies just above the lower hybrid frequency and relatively short wavelengths (1-4 m). The observed lower hybrid waves depend strongly on the position of the PDP relative to the shuttle and the magnetic field direction. Our res ults confirm previous suggestions that the lower hybrid waves are gene rated primarily in the vicinity of the shuttle and that they are drive n by a charge exchange interaction between the ambient ionosphere and a H2O cloud around the shuttle.