Computer Science
Scientific paper
Jan 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt........36f&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF IOWA, 1992.Source: Dissertation Abstracts International, Volume: 54-02, Section: B, page: 090
Computer Science
Scientific paper
During the Spacelab 2 mission the University of Iowa's Plasma Diagnostics Package (PDP) explored the plasma environment around the shuttle. Wideband spectrograms of plasma waves were obtained from the PDP at frequencies from 0 to 30 kHz and at distances up to 400 m from the shuttle. These spectrograms frequently showed interference patterns caused by waves with wavelengths short compared to the antenna length (3.89 meters). Two types of interference patterns were observed in the wideband data: the first type was associated with the ejection of an electron beam from the space shuttle; the second type was associated with lower hybrid waves generated by an interaction between the neutral gas cloud around shuttle and the ambient ionospheric plasma. Analysis of these antenna interference patterns permits a determination of the wavelength, the plasma rest frame frequency, the direction of propagation, the power spectrum and in some cases the location of the source. The electric field noise associated with the electron beam was observed in the wideband data for two periods during which an electron beam was being ejected from the shuttle. This noise always has a broad frequency range at low frequencies (below 10 kHz) and shows clear evidence of interference patterns. The broadband low frequency noise was the dominant type of noise produced by the electron beam. Analysis of the interference patterns produced by this noise shows that the waves have a linear dispersion relation very similar to ion acoustic waves. The waves are believed to be generated by the current of ambient electrons returning to the shuttle in response to the ejected electron beam. The waves associated with the lower hybrid resonance have rest frame frequencies near the lower hybrid frequency and propagate perpendicular to the magnetic field. The occurrence of these waves depends strongly on the PDP's position relative to the shuttle and the magnetic field direction. Our results confirm previous identifications of these waves as lower hybrid waves and suggest they are driven by pick-up ions (H_2O^+) produced by a charge exchange interaction between a water cloud around the shuttle and the ambient ionosphere.
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