Computer Science – Performance
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt.........6a&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF KANSAS, 1995.Source: Dissertation Abstracts International, Volume: 56-11, Section: B, page: 6184.
Computer Science
Performance
Scientific paper
The Galileo spacecraft encountered the Earth once on December 8, 1990 (Earth-I) and again on December 8, 1992 (Earth-II). These flybys provided an excellent opportunity to evaluate the performance of the Energetic Particle Detector (EPD) and establish analysis procedures in a relatively well-known environment. Further, because Galileo's Earth flyby trajectories were very rapid and nearly radial, the radiation belt measurements provided an excellent "snapshot" of trapped radiation. The EPD data agree with and extend the familiar radiation belt empirical models established by the National Space Science Data Center. Because of the rapid flyby and the 20 second spin period of Galileo, great care had to be taken to remove time aliasing from the pitch angle distributions. Large anisotropies were also present due to intrinsic density gradients. Spherical harmonics were fitted to the pitch and phase distributions in order to obtain fluxes from which phase space densities could be computed. The phase space density was calculated from the fitted data for the particles (protons) that conserve the first and second adiabatic invariants and the extracted phase space density was examined for steady state one dimensional pure radial diffusion. The results show that other mechanisms besides pure radial diffusion should be considered. Data were then evaluated for bimodal simultaneous pitch angle and radial diffusion. In this method, the quantity zeta which is related to the first adiabatic invariant, mu, and equatorial pitch angle, alphaeq, by zeta = mu/sin ^2 alpha_{eq } is conserved. The diffusion coefficient as a function of L-shell value, L, is assumed to be of the form D = D_{rm o}L^ {n} where D_{rm o} is the constant value and n is a real number. The exponent of L was determined from the bimodal loss-free, source-free diffusion equation. From this method of data analysis, we were able to obtain very consistent values of n, for most values of zeta. From this result, it is reasonable to claim that bimodal diffusion analysis is a more suitable method than other methods to explain the distribution of the energetic trapped protons in the geomagnetosphere.
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