Effects of Pitch Angle Scattering on Observational Signatures of Nonlinear Charged Particles Dynamics in the Magnetotail

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Daniel Holland

Mentor Department



Numerical simulation of charged particles dynamics in magnetotail-like magnetic fields demonstrate the partitioning of phase space into dynamically distinct regions corresponding to transient, chaotic, and integrable orbits. In turn, this partitioning results in an ion distribution function signature that manifests itself as a series of peaks whose separation is proportional to the 4th root of the particle energy and parameters that describe the mesoscale structure of the magnetic field. The signature has been observed in quiet time satellite data from multiple different spacecrafts. We have developed an ad hoc collision operator that models pitch angle scattering due to random processes in the plasma. In our simulations we launch a uniform incoming distribution of 500,000 particles and measure the outgoing distribution. The distributions are sorted into 8 pitch angle bins (4 incoming, 4 outgoing), to model typical satellite data. We find the predicted peaks in the outgoing distribution are observable at all pitch angles and persist for small to moderate scattering amplitudes and frequencies representative of the quiet time magnetosphere. Furthermore, it is found that the underlying phase space partitioning persists. The KAM surface in the integrable region break up allowing orbits to cross boundaries that are impenetrable in the absence of noise, however the separation in trapping times between the previously integrable, the chaotic, and the transient orbits persists. The robust nature of the phase space structures helps to explain the persistence of the distribution function signature in observed satellite data.



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