plasmasphere as a whole, were not included in the model. Work on including these effects is currently underway. The consequence of having large concentrations of heavy ions in the plasmasphere can be quite serious for the dynamics of the radiation belt relativistic electrons (see Section IV.F). E. Ring Current Modifications Consideration of magnetospheric effects caused by the presence of Ar+ ions may best be ordered in terms of the energies of various plasma constituents in the magnetosphere. This classification is particularly convenient because the beam-stopping mechanism slows down significant numbers of Ar+ to ambient plasma energies ( [[spi:math]]1 eV) while other higher energy Ar+ ions may escape uniform deceleration due to pitch-angle scattering or other smaller scale interactions. For natural magnetospheric particles other than thermal particles, it is customary, for both kinematical and dynamical reasons, to distinguish between particles having E ~ (1-100) keV and those having E [[spi:math]] 100 keV. The former are known as ring-current particles, since they account for the major share of diamagnetic disturbances observable with low-latitude magnetometers at the earth's surface. The latter are known as radiation-belt particles, since they account for most of the radiation damage to hardened spacecraft. The ring current and the radiation belts consist of electrons, protons, and heavier ions trapped in the earth’s magnetic field. Such particles obey the laws of adiabatic charged-particle motion in the first approximation, and their spatial iso-intensity profiles are toroidal in shape (e.g., White, 1966). The ring current and radiation belts are populated with energetic par47
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