Nongyroresonant Pitch Angle Scattering

Details Nongyroresonant Pitch Angle Scattering Nongyroresonant Pitch Angle Scattering

Jun 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...518..974r&link_type=abstract

The Astrophysical Journal, Volume 518, Issue 2, pp. 974-984.

Astronomy and Astrophysics

Astronomy

15

Ism: Cosmic Rays, Plasmas, Scattering, Sun: Solar Wind, Turbulence, Waves

Scientific paper

The spatial transport of charged particles, in a turbulence of slab Alfvén waves and isotropic fast magnetosonic waves, is determined by the pitch angle scattering of these particles. For pitch angle cosines mu larger than the Alfvén speed over the particle speed, this pitch angle scattering is provided by either gyroresonance with the Alfvén waves or transit-time damping (TTD) with the fast-mode component of the spectrum. For smaller pitch angle cosines, however, there is no TTD, and if the particle rigidity is less than 1 GV, in the solar wind there is no gyroresonance possible either. A new nonresonant process is presented here that very efficiently scatters the particles through mu=0 and is due to waves that cannot be in gyroresonance with the particles. The contributions to the particles' mean free path, of this nonresonant scattering process as well as of the TTD and gyroresonant ones, are calculated. The application to low-energy cosmic rays in the solar wind leads to the following conclusions. Below 10^2-10^3 MV, the nonresonant process dominates the gyroresonant one at large pitch angles. Below 0.1-1 MV, the slowest scattering does not occur any longer at large pitch angles but at small ones, via TTD, with a relatively high and flat curve of mean free path versus rigidity. The resulting mean free path, between 10^-2 and 10^5 MV, gives very reasonable fits for the observational data, which diversity could be explained by slight modifications of the turbulence parameters.

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