The ionic charge state composition at high energies in large solar energetic particle events in solar cycle 23

Abstract

The ionic charge states of solar energetic particles (SEPs) depend upon the temperature of the source material and on the environment encountered during acceleration and transport during which electron stripping may occur. Measurements of SEP charge states at relatively high energies (≳15 MeV/nucleon) are possible with the Mass Spectrometer Telescope (MAST) on the Solar, Anomalous, and Magnetospheric Particle Explorer satellite by using the Earth's magnetic field as a particle rigidity filter. Using MAST data, we have determined ionic charge states of Fe and other elements in several of the largest SEP events of solar cycle 23. The charge states appear to be correlated with elemental abundances, with high charge states (~20 for Fe) for all elements in large Fe-rich events. We review the geomagnetic filter technique and summarize the results from MAST to date, with particular emphasis on new measurements in the very large 14 July 2000 SEP event. We compare the charge states determined by MAST with other measurements and with those expected from equilibrium calculations.