Critical Störmer Conditions in Quadrupole and Double Ring‐Current Fields

A theoretical study has been made of the behavior of the critical Störmer pass points for general axially symmetric magnetic configurations. A topological method has been derived to predict the occurrence of the critical Störmer conditions for charged‐particle exclusion. This analytic technique, when applied to geomagnetically interesting fields, should be a useful aid to the understanding of experimental data. The method is applied here to three magnetic geometries: double ring currents with parallel dipole moments and with antiparallel dipole moments, and the axial magnetic quadrupole. The topology of the regions representing allowed motion is treated systematically and the behavior of the critical pass points is illustrated in typical Störmer plots. For the quadrupole and the antiparallel ring system critical pass points are found to occur only out of the equatorial plane. For the parallel ring system, critical points can occur in or out of the equatorial plane. For certain special conditions as many as three simultaneous critical pass points are found, and two simultaneous points occur for a wide range of parameters.