Stochastic Acceleration of Cometary Pickup Ions: The Classic Leaky Box Model
Abstract
The acceleration of cometary pickup ions by magnetohydrodynamic waves at P/GiacobiniZinner is examined in a model where acceleration predominantly occurs downstream of the bow shock throughout the cometosheath where intense magnetic turbulence exists. The mean free path for scattering by the magnetic fluctuations in this region is less than the characteristic dimension of the cometosheath so that pickup ions are rendered isotropic and energized by a modest amount in the process. This principal loss mechanism for the ions is spatial diffusion out of the acceleration region moderated by the selfsame accelerating waves. This particular feature constrains the model in a way that the predicted ion spectrum is uniquely determined by the power spectrum of the magnetic turbulence. At both P/GiacobiniZinner and P/Halley, the turbulence is nonKolmogoroff with a spectral index of 2 resulting in an ion spectral behavior that is approximately an exponential in ion speed, consistent with a recent analysis of the GiacobiniZinner data (see Richardson et al.).
 Publication:

The Astrophysical Journal
 Pub Date:
 June 1989
 DOI:
 10.1086/167510
 Bibcode:
 1989ApJ...341..493B
 Keywords:

 Cosmic Rays;
 GiacobiniZinner Comet;
 Ion Temperature;
 Magnetohydrodynamic Turbulence;
 Magnetohydrodynamic Waves;
 Particle Acceleration;
 Bow Waves;
 Interplanetary Medium;
 Planetary Magnetospheres;
 COMETS;
 ACCELERATION;
 PICKUP;
 IONS;
 MODELS;
 MAGNETOHYDRODYNAMICS;
 GIACOBINIZINNER;
 DOWNSTREAM;
 COMETOSHEATH;
 MAGNETIC EFFECTS;
 TURBULENCE;
 SCATTERING;
 DIAGRAMS;
 CALCULATIONS;
 ENERGY;
 SPECTRA;
 COMPARISONS;
 ICE MISSION;
 SPACECRAFT OBSERVATIONS;
 Astrophysics; Comets;
 COMETS;
 COSMIC RAYS: GENERAL;
 HYDROMAGNETICS;
 PARTICLE ACCELERATION