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


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. This group's work has focused on the Van Allen radiation belts, where trapped energetic electrons may damage spacecraft systems. Their studies have shown that the usual theoretical treatment of electron energization and scattering is inadequate for a complete understanding of 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. These researchers 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. Their MSI 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 subsecond time-scales. They have also shown large angle scattering consistent with observations by the low altitude SAMPEX satellite of relativistic electron microbursts, bursts of energetic particles lost from the radiation belts to the atmosphere.

The the twin Radiation Belt Storm Probe (RBSP) satellites, for which the University of Minnesota is the electric field instrument PI, were launched in August 2012 and continue to provide unprecedented measurements of radiation belt wave activity and the associated particle energization and loss. RBSP measurements of high time resolution electric and magnetic field waveforms are being used with filter bank data (continuous records of peak and average wave amplitudes) to develop more detailed spatial maps and occurrence statistics for large amplitude waves in the radiation belts. These data will be used with this group's simulation results to model rapid changes in trapped radiation belt particle populations in response to magnetic storms. The RBSP mission also includes a coordinated Balloon Array for RBSP Relativistic Electron Losses (BARREL) to allow multi-point measurements of relativistic electron scattering and loss to the atmosphere. The first 20-balloon campaign was completed in early 2013 and provides detailed measurements of energetic particle precipitation to the atmosphere in conjunction with the twin RBSP satellites. A second campaign is scheduled for 2014, and the resulting data will be used to validate models developed through the Cattell group's simulation studies. 

A bibliography of this group’s publications acknowledging MSI is attached.

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