Development of pitch angle anisotropy and velocity diffusion of pickup ion shell distribution by solar wind turbulence
Abstract
It is well known that intrinsic solar wind turbulence can cause rapid pitch angle diffusion of newborn ions and subsequently form a nearly isotropic shell distribution. If the initial shell distribution is subjected to a continuous influence of turbulence, the thickness of the shell distribution may increase as a result of diffusion in velocity space. Since the pitch angle diffusion rate is much larger than the velocity diffusion rate, it is often anticipated that the ion distribution will remain fairly isotropic. However, the velocity diffusion process is itself pitch angle dependent, and as a result, significant pitch angle anisotropy may develop at the early stage of evolution. This result can be of importance, particularly if the pickup ion density is sufficiently large, because the pitch angle anisotropy may excite collective instabilities that can further increase the wave level, thus accelerating the diffusion process. In this work detailed analyses of the pitch angle and velocity diffusion processes of initial shell distribution subjected to a continuous influence of solar wind turbulence are presented.
 Publication:

Journal of Geophysical Research
 Pub Date:
 October 1990
 DOI:
 10.1029/JA095iA10p17085
 Bibcode:
 1990JGR....9517085Y
 Keywords:

 Anisotropy;
 Ion Distribution;
 Ionic Diffusion;
 Magnetohydrodynamic Waves;
 Pitch (Inclination);
 Plasma Turbulence;
 Solar Wind;
 Bessel Functions;
 Green'S Functions;
 Astrophysics;
 Ionosphere: Ionospheric disturbances;
 Space Plasma Physics: Turbulence