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Research Abstracts Online
January - December 2011

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University of Minnesota Twin Cities
College of Science and Engineering
School of Physics and Astronomy

PI: Cynthia A. Cattell

Using Particle Tracing Codes to Understand Acceleration of Relativistic Electrons via Electrostatic and Electromagnetic Waves

A key longstanding problem in space and astrophysical plasmas is determining the mechanism by which electrons can be accelerated to relativistic energies. Previous work by this group at MSI focused on the Van Allen radiation belts, where the MeV electrons can damage spacecraft systems. These researchers’ studies have shown that the usual theoretical approach to studies of electron energization and scattering is inadequate to understanding radiation belt dynamics. Most current theoretical studies of whistler acceleration take a quasi-linear approach and assume whistler amplitudes on the order of 1 mV/m. The researchers have discovered narrow-band whistler-mode waves in the outer Van Allen belt with electric field amplitudes an order of magnitude larger than previously observed and have very recently discovered similar large wave associated with intense ground transmitters. Particle-tracing results have shown that these large waves (>100 mV/m) result in nonlinear coherent effects that can produce energization to several MeV on the short time-scales. The researches have also shown large angle scattering consistent with observations by the low altitude SAMPEX satellite of so-called “relativistic electron microbursts,” which are particles lost from the radiation belts to affect the atmosphere. Recently these researchers have also started studies of whistler acceleration in the solar wind. They have continued code improvement and, in addition, are improving diagnostics for the three-dimensional code. The researchers are continuing their improvements in to the code that models a single magnetic flux tube to examine effects of electrostatic waves, in addition to electromagnetic waves, to examine electron energization by the newly discovered waves, as well as in other regions where relativistic acceleration is occurring, including the solar wind and magnetotail reconnection. They examine acceleration of ions during magnetic “superstorms” using the three-dimensional code to compare to satellite observations of long-duration energy banded ions. Results are critical to the upcoming NASA Radiation Belts Storm Probe mission on which the University of Minnesota is an Instrument PI and the Solar Probe mission for which this group was recently selected.

Group Members

Aaron Breneman, Research Associate
John Dombeck, Research Associate
Meghan Eskolin, Undergraduate Student
Lily Hanson, Undergraduate Student
Kristopher Kersten, Graduate Student
Ilan Roth, Space Sciences Laboratory, University of California, Berkeley, California