Coronal particle trapping revisited

We re-examine the idea of long-term particle storage in the solar corona in the context of modern PFSS (potential-field source surface) magnetic models. As pointed out by H. Elliot in 1964 and others since then, such particles could be energetically important, at the level of some large fraction of the magnetic energy density B2/8π. We estimate the distribution and time scales of particle trapping by using representative PFSS coronal models from the Schrijver-De Rosa SolarSoft code. As the coronal field simplifies during solar minimum, it approaches axisymmetry and thus contains volumes inaccessible to charged particles under the guiding-center approximation. We conclude that time scales can be sufficiently long, so long in fact that the azimuthal drift time scale (third adiabatic invariant of guiding-center motion), for the large-scale dipolar configuration characteristic of solar minimum, can exceed one solar cycle. We discuss the possible sources of trapped particles, starting with the basic CRAND (cosmic-ray albedo neutron decay) mechanism, and relate their X-ray and γ-ray signatures to future observational capabilities including the Sentinels spacecraft.