College of Science & Engineering
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 has focused on the Van Allen radiation belts, a region where the earth’s magnetic field traps large populations of energetic electrons. Relativistic electrons are often observed in the radiation belts, and it is in this region and at these energies that electrons are of particular interest, potentially damaging geosynchronous spacecraft and precipitating into the earth's atmosphere. Theoretical studies of wave-particle interactions often employ quasi-linear theory on the assumption that wave amplitudes are small. This group's observational studies indicate that this assumption may not be valid in the near-earth environment, and previous simulations on MSI resources have shown that the interaction of electrons with large amplitude waves may lead to nonlinear coherent effects that can result in scattering and energization of electrons to several MeV on subsecond time-scales.
Another important acceleration mechanism is associated with interplanetary shock impacts. This group is developing new simulations to investigate how these shock impacts propagate through the magnetosphere and interact with energetic ions and electrons. Interplanetary shocks are associated with some of the largest geomagnetic storms with the potential to cause damage to space-based assets. These models will employ data-based electric field models using measurements from the group's electric field instruments on the RBSP satellites.
The results of these simulations are critical to the NASA Radiation Belts Storm Probe mission, on which the University of Minnesota is an Instrument PI, and to the recently launched Parker Solar Probe mission for which the University supplied a high time resolution waveform instrument.
In addition to the continued study of radiation belt electron acceleration, this group is adapting the whistler-mode code to investigate interaction with near-monochromatic waves in the solar wind. These large amplitude waves were discovered by this group in the STEREO satellite dataset and they have modified the operation of their instrument to obtain longer waveform samples to better asses the structure of these waves and their role in modifying solar wind electrons. The investigations of solar wind electron acceleration are very relevant to the NASA Parker Solar Probe mission, on which this Principal Investigator is a co-investigator. The potential impact of these waves on propagation of solar energetic electrons and cosmic rays is critical to understanding effects of space weather for future interplanetary missions.