Relevance of supra-thermal ion observations for heuospheric physics

Recent studies show that suprathermal particles with energies of a few times that of the bulk solar wind up to 100s of keV/nuc contribute significantly as seed particles for acceleration close to the Sun and indeed throughout the heliosphere. However, the origin of these suprathermal particles is largely unknown at this time. Moreover, the suprathermal reservoir is not a fixed quantity, but varies with time and is also expected to vary in space. Consequently, the effects of the inherent variability of the suprathermal ions on the accelerated populations are completely unknown. It is therefore important to make high-time resolution measurements of the composition and angular distributions of the suprathermal ions in the inner heliosphere. Here we describe the type of challenging but critical measurements that are needed to characterize properties of the suprathermal energy regime. Such measurements will ultimately enable closure between observations and various particle acceleration models.