MeV acceleration processes for heliospheric heavy ions

Abstract

Observations of energetic ions of solar origin in the heliosphere suggest the existence of two main energization sites with different physical mechanisms: (1) impulsive mechanism on the flaring coronal magnetic field – via resonant interaction, presumably with low-frequency electromagnetic waves; (2) gradual mechanism around the propagating, interplanetary shock – by interaction with quasi-static inhomogeneous electromagnetic structure and low-frequency Alfvenic turbulence. While the coronal process enhances a subset of rare elements, the interplanetary interaction energizes most of the elements of coronal/solar wind origin. In the impulsive events, according to recent models, a significant fraction of heavy elements which reside on the active flaring flux rope is energized; the resonant interaction operates mainly on Fe and other heavy elements with high charge states. In the gradual events main energization occurs close to the Sun at low Mach numbers; significant interplanetary enhancement of energetic ion fluxes requires a narrow scale length in the propagating shock. Coupling of both processes results in the final heliospheric distribution function of the heavy elements. The enhanced energetic heavy ion population may have a profound impact on human space exploration in the interplanetary space as well as in the resulting trapped radiation in the magnetosphere.