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All whistlers are not created equally: Scattering of strahl electrons in the solar wind via particle‐in‐cell simulations
Author(s) -
Saito Shinji,
Gary S. Peter
Publication year - 2007
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2006gl028173
Subject(s) - whistler , pitch angle , physics , electron , scattering , atomic physics , solar wind , computational physics , magnetic field , optics , geophysics , nuclear physics , quantum mechanics
Solar wind observations show that suprathermal electrons (70 eV ≲ Energy ≲ 1 keV) of the magnetic‐field‐aligned “strahl” component have broader pitch‐angle distributions than are predicted by adiabatic theories of solar wind expansion. Magnetosonic‐whistler fluctuations propagating toward the Sun at k × B o = 0 (where B o is the background magnetic field) have a strong cyclotron resonance with suprathermal electrons propagating in the anti‐Solar direction along B o . This resonance enables strong pitch‐angle scattering; thus whistlers are a likely source of the observed strahl broadening. Particle‐in‐cell simulations in a magnetized, homogeneous, collisionless plasma of electrons and protons are used to study the response of a strahl‐like electron component to whistler fluctuation spectra. If the whistler anisotropy instability is excited via the initial application of T ⊥ / T ∥ > 1 to the electron core component, the resulting electron scattering leads to strahl pitch‐angle distributions which decrease in width as electron energy increases. In contrast, if a power spectrum of whistler fluctuations proportional to k −3 is initially applied to the simulations, the resulting electron scattering leads to strahl pitch‐angle distributions which increase in width as electron energy increases.