Large Amplitude Whistler Waves: Nonlinear Dynamics and Interactions

• Author / Creator

  Karbashewski, Scott G

• In this thesis we present Particle-in-Cell (PIC) plasma simulations designed to model large amplitude whistler waves. There are significant nonlinear effects that arise due wave-wave and wave-particle interactions. There are two related sections to this report: one investigating the evolution of the nonlinear dynamics of obliquely propagating whistler waves, and the other investigating the wave-wave coupling between whistler waves and electrostatic modes. Recent satellite observations by \textit{Cattell et al. (2008)}~\cite{cattell2008} have identified the presence of large amplitude whistler plasma waves in the Earth's outer radiation belt ($3 \leq L \leq 15$) that propagate obliquely with respect to the Earth's magnetic field. \textit{Cattell et al. (2008)} suggest that these large amplitude whistlers are a mechanism for the rapid acceleration of radiation belt electrons to relativistic energies. Previous efforts have been made in \textit{Yoon (2011)}~\cite{yoon2011} to simulate these large amplitude whistlers and the resulting particle acceleration using a cold electron fluid model with test particles in the nonlinear wave fields. Additionally, nonlinear effects such as particle trapping in \textit{Kellogg et al. (2010)}~\cite{kellogg2010} and wave steepening in \textit{Yoon (2011)} have been identified as being important to the wave dynamics. We present results from a PIC simulation with self-consistent electromagnetic fields to account for the feedback effects of particles on the large amplitude whistler wave. Using initial conditions to launch a large amplitude plasma wave that is consistent with the dispersion relation for oblique whistler waves we characterize the nonlinear effects in the wave evolution. We show that the wave fields are capable of thermalizing a self-consistent electron distribution from $\sim 1~\textrm{eV}$ to $\sim 100~\textrm{eV}$, and can accelerate a non-interacting seed population from $\sim 100~\textrm{eV}$ into the range of $\sim 20-30~\textrm{keV}$. We highlight the presence of compressional wave steepening effects as well as particle trapping and wave field distortion and damping that follow thereafter. Finally, we present wave amplitude scaling relations for three important time scales: wave steepening time, particle trapping time, and particle acceleration time. The second set of simulations revolve around a satellite observation by \textit{Agapitov et al. (2015)}~\cite{agapitov2015} of the parametric decay of a whistler wave into a backscattered whistler and an electron acoustic wave. It is claimed that this process is the source of spiked electrostatic fields in the outer radiation belt observed by \textit{Mozer et al. (2013)}~\cite{mozerTDS} that have been shown by \textit{Artemyev et al. (2014)}~\cite{artemyevTDS} to rapidly accelerate $\sim 10-100~\textrm{eV}$ electron populations into the $\sim 1-2~\textrm{keV}$ range. We present a set of Darwin PIC simulations investigating the interactions of parallel electromagnetic whistler waves with electrostatic plasma modes. By adding external wave fields consistent with the whistler dispersion to the self consistent electromagnetic fields we launch a whistler wave in different plasma conditions to isolate interactions with the Langmuir, ion acoustic, and electron acoustic wave modes. We identify a nonlinear coupling to the Langmuir mode that results in nonlinear electrostatic structures and modification to the electron velocity distribution at the whistler phase velocity. With moving ions we present multiple parametric decay channels of a whistler into a backscattered whistler and ion acoustic mode that show remarkable agreement with predictions made using a simple ponderomotive force as the coupling mechanism. However, a similar process does not occur for the electron acoustic mode as the Langmuir coupling dominates in this scenario. Drawing from the ion acoustic results and the conditions in \textit{Agapitov et al. (2015)} we suggest that it may be necessary to have a relative drift between hot and cold electron populations to observe the parametric decay of a whistler wave into an electron acoustic wave in space plasma conditions.

• Subjects / Keywords

  • Whistler
  • Oblique
  • Nonlinear
  • Plasma

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R33776B4R

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.