Trapped Particle Motion in Magnetodisk Fields

Abstract The spatial and temporal characterization of trapped charged particle trajectories in magnetospheres has been extensively studied in dipole magnetic field structures. Such studies have allowed the calculation of spatial quantities, such as equatorial loss cone size as a function of radial distance, the location of the mirror points along particular field lines ( L ‐shells) as a function of the particle's equatorial pitch angle, and temporal quantities such as the bounce period and drift period as a function of the radial distance and the particle's pitch angle at the equator. In this study, we present analogous calculations for the disk‐like field structure associated with the giant rotation‐dominated magnetospheres of Jupiter and Saturn as described by the University College London/Achilleos‐Guio‐Arridge (UCL/AGA) magnetodisk model. We discuss the effect of the magnetodisk field on various particle parameters and make a comparison with the analogous motion in a dipole field. The bounce period in a magnetodisk field is in general smaller the larger the equatorial distance and pitch angle, by a factor as large as ∼8 for Jupiter and ∼2.5 for Saturn. Similarly, the drift period is generally smaller, by a factor as large as ∼2.2 for equatorial distances ∼20–24 R J at Jupiter and ∼1.5 for equatorial distances ∼7–11 R S at Saturn.