Physics – Plasma Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsh41b0757s&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SH41B-0757
Physics
Plasma Physics
7800 Space Plasma Physics, 7807 Charged Particle Motion And Acceleration, 7843 Numerical Simulation Studies, 7851 Shock Waves, 7867 Wave/Particle Interactions
Scientific paper
Diffusive shock acceleration (DSA) theories predict ion energy spectra of power-law forms. On the other hand, the energy spectra obtained at terrestrial bow shocks and in hybrid simulations show exponential forms over a wide energy range (from several keV up to a few hundreds keV). Loss of ions from the acceleration region (by, e.g., cross-field diffusion) is supposed to cause this difference. However, even in one-dimensional quasi-parallel shock simulations where cross-field diffusion is inhibited, the spectra are still exponential. A model where the spectrum develops from an exponential to power-law form in time has not been fully examined because of the long time scale for the stationarity. Here we have performed a number of hybrid simulations to investigate a dynamics of high energized ions in another point of view. To create the high energized ions in a short time we have placed non-physical wall in the upstream region. This wall elastically reflects accelerated non-thermal ions in the local fluid frame. Although all the accelerated particles can return from upstream to the shock surface which is the same assumption as that in the diffusion convection (DSA) model, the returning ratio in the downstream region shows lower than the ratio assumed in the DSA model. This is the main reason that the energy spectra shown in the hybrid simulations are exponential form. Loss of ions from the acceleration region is more important process in the downstream region than in the upstream region.
Fujimoto Minoru
Scholer Manfred
Sugiyama Takanori
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