Abstract
A fundamental problem of cosmic-ray diffusion theory is pitch-angle scattering at 90°. For isotropic and anisotropic turbulence, the 90° problem leads to an infinitely large parallel mean free path. In this Letter, the second-order quasi-linear theory for cosmic-ray scattering parallel to a mean magnetic field is generalized for isotropic turbulence. It is shown that, in contrast to classic quasi-linear theory, the second-order theory provides nonvanishing scattering through 90° even for magnetostatic turbulence. The problem of 90° scattering is thus solved, because the comparison with simulations shows good quantitative agreement. It is also shown that the Fokker-Planck coefficient for pitch-angle scattering has its maximum at 90°.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
