Physics – Atomic Physics
Scientific paper
Jan 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990phdt.......100s&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF MARYLAND COLLEGE PARK, 1990.Source: Dissertation Abstracts International, Volume: 51-11, Section:
Physics
Atomic Physics
1
Ring Current, Energy Loss
Scientific paper
We have studied the problem of ion transport and loss in the quiet terrestrial ring current, extending the energy range of the standard radial diffusion model, developed for radiation belt particles, to the ring current ions and have compared it with experimental data. We compiled a data set from all quiet days (with good local time coverage) seen by the AMPTE/CCE/CHEM instrument in near equatorial orbit at L-shells from 2-9 RE . For the first time, we have ionic composition information in an energy range that includes the bulk of the ring current ions, 1-300 keV/e. We used a standard radial diffusion model that incorporates a source boundary at large distances from the earth, 7.5 R_ {E}, and follows the ions as they diffuse earthward while undergoing charge exchange and Coulomb energy loss. We improved on the model loss processes by incorporating the latest atomic physics cross sections from the literature. We also employed a chi ^2 minimization routine to fit the amplitudes of the diffusion constants, but we were unable to fit the data (to within a factor of 10) over 50% of the energy -radial range of the data set. Some of the deviation from the model is explained by convection-produced, local time (LT) dependencies in the data that are ignored by the azimuthally averaged model. But even accounting for this low energy correction (<30 keV), we propose there exists an additional transport term at low L-shells (< 4.0 RE) that does not obey the expected L^6 power law. We argue that scattering processes are responsible for this additional transport, and suggest a collisional mechanism as a possible candidate. In addition, we develop a new model that incorporates LT variations into the radial diffusion model. This new model can be shown to handle both convection and diffusion simultaneously. It also predicts a LT-dependent radial diffusion coefficient. We present some data in this reformulation to show the importance of low energy convection on the radial diffusion problem.
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