Transport and acceleration of anomalous cosmic rays in the inner heliosheath

Abstract

The transport and acceleration of anomalous cosmic rays in the inner heliosheath is studied. A unique two‐dimensional hydrodynamic numerical model is used to calculate the interaction of the solar wind and the local interstellar medium, neutral hydrogen, and pickup ions. The divergence of the flow, heliospheric magnetic field, and Alfven speed are calculated and then inserted into model which calculates cosmic ray transport and acceleration in this heliosphere by solving the Parker particle transport equation. We show that adiabatic heating and stochastic acceleration plays a major role in explaining Voyager 1 observations both at the termination shock and in the inner heliosheath. While the inclusion of adiabatic heating in a numerical modulation model results in the correct spectral shape of accelerated anomalous particles for energies ≤∼10 MeV at the termination shock, stochastic acceleration effectively accelerates these particles further to anomalous energies out in the inner heliosheath. These accelerated particles are then modulated back inward, resulting in realistic radial gradients as well as an upturn in the anomalous cosmic ray spectra. A parameter study is also done to illustrate the sensitivity of these acceleration processes to different diffusion coefficients.