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Study of Wave‐Particle Interactions for Whistler Mode Waves at Oblique Angles by Utilizing the Gyroaveraging Method
Author(s) -
Hsieh YiKai,
Omura Yoshiharu
Publication year - 2017
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1002/2017rs006245
Subject(s) - physics , electron , whistler , computational physics , pitch angle , cyclotron resonance , test particle , oblique case , resonance (particle physics) , particle acceleration , scattering , magnetic field , kinetic energy , electromagnetic radiation , atomic physics , cyclotron , optics , classical mechanics , quantum mechanics , geophysics , linguistics , philosophy
We investigate the properties of whistler mode wave‐particle interactions at oblique wave normal angles to the background magnetic field. We find that electromagnetic energy of waves at frequencies below half the electron cyclotron frequency can flow nearly parallel to the ambient magnetic field. We thereby confirm that the gyroaveraging method, which averages the cyclotron motion to the gyrocenter and reduces the simulation from two‐dimensional to one‐dimensional, is valid for oblique wave‐particle interaction. Multiple resonances appear for oblique propagation but not for parallel propagation. We calculate the possible range of resonances with the first‐order resonance condition as a function of electron kinetic energy and equatorial pitch angle. To reveal the physical process and the efficiency of electron acceleration by multiple resonances, we assume a simple uniform wave model with constant amplitude and frequency in space and time. We perform test particle simulations with electrons starting at specific equatorial pitch angles and kinetic energies. The simulation results show that multiple resonances contribute to acceleration and pitch angle scattering of energetic electrons. Especially, we find that electrons with energies of a few hundred keV can be accelerated efficiently to a few MeV through the n = 0 Landau resonance.