Dynamics of a charged particle in a spiral field

Abstract

The adiabatic guiding center motion of an energetic charged particle in an idealized representation of the interplanetary magnetic field is discussed. Expressions are presented for all drift velocity components. A comparison of these drifts establishes that, for the cases of physical interest, the electric drift velocity is by far the dominant drift velocity. Considering only the electric drift velocity, an expression is derived for the time of flight of a particle leaving the sun. Similarly, it is shown analytically that the particles remain attached to the same field line on which they left the sun, thus indicating their point of origin. High-energy unscattered particles are shown to be rapidly channeled down the field lines, which results in a highly anisotropic particle distribution in the vicinity of the earth. These analytic results are in excellent agreement with numerical integration of the complete drift equation and compare favorably with the experimental data.