## Doctoral Dissertations

Spring 1998

Dissertation

Physics

#### Degree Name

Doctor of Philosophy

Eberhard Mobius

#### Abstract

This thesis have presented the first detailed study of the sources and the acceleration of energetic He$\sp+$ ions in front of the Earth's bow shock, using data from AMPTE/IRM and AMPTE/CCE.

Based on observations of energetic He$\sp+$ ions during an event when the bow shock was an almost perfect perpendicular shock, we compared the results of a simulation to the observed event. The model provides a good quantitative description of the phase space distribution of the gyrating ions. A large portion (approximately 63%) of the incident pickup ions are reflected and gain energy in the interaction. It is also consistent with their spatial distribution in front of the shock. It is shown that a significant fraction of the upstream ions undergo more than one reflection at the bow shock, and gain substantial energy in this interaction.

At the quasi-parallel shock, by calculating the omnidirectional distributions of $\rm H\sp+,\ He\sp{2+},\ He\sp+$ and O$\sp+$ ions upstream of the shock, as well as a comparison of the observed spectra upstream of the shock and m the magnetosphere with results from the calculations, we concluded that He$\sp+$ is locally accelerated. The subsequent modeling of the injection and diffusive acceleration at the shock presented evidence that pickup ions can be injected and accelerated more efficiently than solar wind plasma.

These results have important implications concerning acceleration of pickup ions and anomalous cosmic rays.

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