PREACCELERATION OF ANOMALOUS COSMIC-RAYS IN THE INNER HELIOSPHERE

Because of the apparent difficulty in accelerating previously unaccele rated pickup ions locally at the solar wind termination shock, a model for anomalous cosmic-ray protons is considered in which the initial a cceleration of pickup ions to similar to 10-20 MeV occurs in the inner heliosphere. These accelerated pickup ions are assumed to be accelera ted either by propagating interplanetary shocks or by some other, unsp ecified process. Voyager 2 Low-Energy Charged Particle (LECP) observat ions at low energies are used to normalize their spectra. The ions are then transported to the termination shock, where they are further acc elerated to anomalous cosmic-ray energies. We use a well-established t ransport model to simulate this process. In this model, the two-dimens ional cosmic-ray transport equation is solved using the assumed (and n ormalized) source of energetic particles (similar to 0.01-20 MeV) loca ted at 10 AU. We show that the computed spectra at higher energies (gr eater than or similar to 100 MeV) are consistent with observed anomalo us cosmic-ray fluxes and suggest that interplanetary shocks, especiall y those in the inner heliosphere, may play an important role in the in itial acceleration of pickup ions leading to anomalous cosmic rays.