Observation of Injection and Pre-Acceleration Processes in the Slow Solar Wind |
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Authors: | George Gloeckler |
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Institution: | (1) Dept. of Physics and IPST, University of Maryland, College Park, MD, 20742, USA, and;(2) Dept. of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48109, USA |
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Abstract: | Knowledge of injection and pre-acceleration mechanisms of ions is of fundamental importance for understanding particle acceleration
that takes place in various astrophysical settings. The heliosphere offers the best chance to study these poorly understood
processes experimentally. We examine ion injection and pre-acceleration using measurements of the bulk and suprathermal solar
wind, and pickup ions. Our most puzzling observation is that high-velocity tails, extending to at least 60 keV/e - the upper
limit of measurements -, are omnipresent in the slow, in-ecliptic solar wind; these tails exist even in the absence of any
shocks. The cause of these tails is unknown. In the disturbed solar wind inside CIRs and downstream of shocks and waves these
high-speed tails in the distributions of H+, He+ and He++ become more pronounced and more complex, but with the shapes of the tails showing the same dependence on ion speed for the
different species. Pickup hydrogen and helium are found to be readily injected for subsequent acceleration to MeV energies,
and thus are the dominant source of CIR-accelerated energetic ions. Competing sources of MeV ions heavier than He are: (1)
heated suprathermal solar wind observed downstream of CIR shocks, (2) interstellar N, O and Ne, and (3) the newly discovered
heavy pickup ions from an extended inner source inside 1 AU. Our main conclusion is that mechanisms other than the traditional
first-order shock acceleration process produce most of the modestly accelerated ions seen in the slow solar wind.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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