Department of Physics
Moulton Hall 311
Campus Box 4560
Normal, Il 61790-4560
Welcome to the Department of Physics.
Illinois State University Physics Department
Presented at the Argonne Symposium for Undergraduate Research
We have modeled ion velocity distributions in the near-Earth magnetotail, the part of the Earth's magnetosphere on the anti-sunward side of the planet. The megnetotail is thought to be the crucial region in energy storage and release during magnetospheric substorms, so an understanding of the plasma properties in this region is essential. Velocity distribution functions are measured on satellites and give a great deal of information about the dynamics of ions and electrons in the plasma. Our magnetic field model is a standard one consisting of a Harris current sheet with a uniform normal component. In our simulation, we use a "virtual detector" at a fixed location in the model field and trace particles from the detector, backwards in time, until they reach a source region. In this study the source region is located in the large z asymptotic region above and below the current sheet field reversal region, one of the known sources of plasma for the magnetotail plasma sheet. We have found structuring in the ion distributions consisting of peaks and valleys in the pitch angle distribution for precipitating particles near the edge of the magnetic field reversal. The structuring only occurs for a certain range of energies and field parameters. We have re-binned our simulation data to see how detector resolution affects the observability of these structures. We find that the CPI detector on the GEOTAIL spacecraft has the capability to resolve such structures if observations are taken at a fixed gyrophase. The sturctures depend on gyrophase such that as phase increases from 0 to 360 degrees, the ridges move to higher parallel velocities. If the phase angles are averaged over, however, the structuring cannot be as easily resolved, and a higher resolution detector may be required. If observable, these particle structures could be used as a remote sensing method for magnetotail fields and may help us better understand the interaction between the magnetotail and the polar ionosphere during ion precipitation.